Bit of extra history I discovered as a building surveyor: large air bricks were often placed above the DPC level to ventilate larders or pantries in houses built before the widespread use of fridges. You can normally identify these 1. Where they directly align with a large larder or pantry and 2. If it was on the north most facing side of the house out of direct sun light. Roger is right most of these ‘wall airbricks’ are to ventilate a room though.
my Mum had a "pantry" under the stairs before the advent of electric fridges, comprising of a zink screen in front of an air brick and food sat on a marble slab, one tuesday she had a nasty shock and chucked half a joint of beef crawling with maggotts and blueflies, that was dinner, bastards.
My 1911 terrace has lime mortared cavity brick walls. The cavity is ventillated externally by huge cast iron vents a the top and bottom, plus gaps into the cavity above all the sash window frames. After 100+ years the walls are beautifully stright with apparently no issues with corrosion of the wall ties, but I hate to think what could happen if I messed with the cavity ventilation in any way.
When I was an apprentice, regs were just introducing insulation into 50mm cavities! My mentor always moaned about it bridging the cavity and reducing air circulation and the batts making rags on the ties causing damp. The price per 1000 didn't go up though, I think that was his main gripe!
I was always stunned by the sheer simplicity of cavity wall insulation sales folk. They'd knock on my door and ask if I want it, I'd tell them it's a Victorian house - with solid brick walls. They'd say 'oh'... and then go next door, and enxt door to that etc. In a terrace of houses exactly the same, getting the same answer each time. They have now moved onto the highly toxic and flamable external insulation. So they're having to be told what a conservation area is by everyone that answers.
I'm in a conservation area and I'm having external wall insulation. It was approved with no conditions by the council. It would only be if the parish council are staunch traditionalists or if the house is listed that you might have any issue.
It would only take one, probably elderly, houseowner, who doesn't know/understand they have single skin walls, to say yes. Then they could turn up, drill a few holes in the walls, make some noise and pack up.
@@peterthebricky Just looked one up, has Class E fire rating, which means it is combustable and has a high contributes to the fire. Edit; The class E was a polystyrene based one. I can see Kingspan have some class C and Rockwool has an A1 - so if you are getting external insulation, go for something that seems fireproof like Rockwool.
Housing designed with vented cavities ( 1920s,30, 40, 50, ) are best left vented. The cavities are open at wall plates for ventilation of roof timbers and timber floors. This method of construction was practical, to prevent dry rot.
Okay... I am an Engineer (old school), who is in the later stages of building a timber frame passive house. I have a rendered block outer leaf with 50mm cavity. the timber frame has a semi permeable foil/fabric layer onto 9mm OSB sheathing, which in turn nailed to 235mm inner leaf timber stud work. The top of the cavity wall is closed off with fire socks. The semi permeable membrane works on an "Osmosis" method where it allows residual moisture content in the frame to escape into the cavity. If that cavity is fully closed and saturated with moisture, like after having heavy driving rain then sun heating the wall, creating high humidity, this effect will be diminished. Also by having cavity trays at DPC level and above Lintels, there are weep vents at 900mm intervals, so there will be air movement to a degree. The fire socks around the roof line will stop air to the attic space, and also fire if it does happen. I believe that having a closed off cavity will eventually impact on the timber frame in the future. Because of my fears, probably unfounded, I will be painting the render with ProPerla paint when the weather warms up. Apparently, hydrophobic paint is the way to go nowadays.
@adamsweet3587 could you not install a soffit/fascia vent so any moisture goes outside and you maintain the firestop..? I would also paint the render...
How does cavity 'saturate' with moisture after heavy rain? What is the point of building an external wall if this occurs - bricks absorb / pass water through VERY slowly so unless under water or direct heavy rain for weeks and weeks, its not going to happen! If you are building with an internal breathable skin then that MUST be ventilated on its outer face - the design is not correct if not, you are mixing methods and not in a good way!
As long as you're weep vents are 65mm high and you have them at 900 centres above and below any fire socks and at dpc level at the ground, this should be sufficient to properly vent the cavity. Here in Scotland for timber frame construction, the regs require cavity vents of at least 300mm2 every 1200mm. You should get more than that if your vents are at 900 centres.
@@kawazukisoddbits2717 If you have a closed cavity and have a damp inner side of the outer leaf, and after a period of driven rain, the eventual sun will initial warm that wall to create a more humid environment, until the wall outside dries, to then pull back the moisture to the outside. The levels here maybe very small and will not affect the inner leaf and I am probably being overly too critical. Traditionally cavities were open at the top and roof eaves had ventilation either in the soffits or as vent bars sitting on top of the fascia boards(which the tile sat on), so you had a vented loft space. My house is on a hill (in Cornwall), exposed, South facing, and the South West weather fronts do push hard on my facing walls.
@@WilliamBell-tj9sq Yes, I do have weep vents at DPC and Lintel levels, so when my exposed house experiences high winds, which it does, it will force air from the exposed side around to the other side which will be at lower air pressure. I am probably being overly critical of my situation.
Here in Australia the top of the cavity and the cavity itself are left open to vent the cooler under floor air. This keeps the house cooler in summer and keeps the underfloor drier.
I have a 1928 built detached house with a cavity. The parlour was built with a suspended floor. There are air bricks front and rear, wind blows right through. However, the cavity has openings below floor level so wind blows up the unfilled cavity. There are air bricks level with the top of the 1st floor windows, these are unsleeved with cast iron sliding vents. The cavity is open at loft level. Effectively I have a single skin house as the walls are cooled (but dry) by cold wind blowing through. The walls inside are really cold. I have a lot to sort out!
Hi Roger, At Last...!!! It took me forever to find a video on cavities. It seems everyone talks about window reveals and door reveals, but you are the first I can find to talk about the top of the cavity. Thank you for clearing this up. There is not much information on the top (eaves) of the cavity and how it should be sealed. Also it seems that not many of the eaves I have seen on older houses seem to be sealed in the construction. Maybe an oversight or just lazy builders. Thanks Roger and the Skill Builder team...
In a brick/block built building with a cavity that is fully sealed, how does moisture from driving rain seeping into the cavity escape? If the cavity warms up and has moisture, shouldn't there be somewhere for the moisture to go? Could a fully sealed cavity with no air flow cause dry rot? Does 'Rockwool' style cavity insulation allow air flow when the cavity is fully filled with it? Does it soak up and hold moisture or does it transfer it to the internal skin? These are the discussions I have on site consistently over the years and everyone has a different view. Personally, as a Bricklayer, I never seal the cavity at the top, I don't insert air bricks to the cavity and I prefer to use Rockwool type insulation when I can. I've never experienced any issues but I still don't know if that's the right way to go or not after more than 40 years on the trowel.
It seems that some people confuse ventilation, draining and breathability. In the east of England where i now live most buildings up to 1960 are built with solid walls because it's a dry 2:49 climate and the bricks were low poroucitty with lime mortar; hence no need for cavities. There's no point allowing wet cold air to circulate against the internal skin which is transmitting moisture from the inside thus causing condensation which shows as damp on the bottom of the inside wall.
Have you been living under a rock for the past 30 odd yrs? Fully filled cavities have been used and APPROVED for use in this time! Bad workmanship is the cause of damp penetration!
@ It is like putting a sponge inside the cavity retaining moisture . It bridges the cavity and draws water across the dry interior skin. It also promotes corrosion of the wall ties. Unless the exterior face of the wall is sealed with a properly sealed foil and reasonable gap maintained water will track across. It is such a stupid idea approved by officials that have had a mind fart. It has never been legal in my country. We frankly still have our brains turned on.
@ It cannot work, you are putting a sponge inside the cavity and tracking moisture to the dry skin. You are also jeopardising the structural integrity of the building by creating a moisture soak at every wall tie encouraging them to corrode. It could work with foil faced insulation but a cavity should still be maintained. Whoever approved that 30 years ago was having a brain fart. It’s not legal where I come from we still have our brains turned on. Seriously it is absolutely nuts, and fixing it with a paint on sealant is bs too. It’s poor building practice.
@davidconnolly7346 not arguing but where are you from. I'm in essex UK, I've laid bricks since 1986 with full fill insulation in 95% of the cavity work. I've yet to have a comeback. Modern full fill bats are water repellent but the older stuff not so much
The primary role of the cavity is to waterproof the building not provide a location for insulation. A way better method if you want additional insulation is brick veneer with the insulation within the interior timber wall. We leave our cavities open in Australia. We get so 3:04 much rainfall too. Cavities get a lot of water inside them, they also need ventilation to dry them out. It’s been working for 100’s of years. What do you do in England when all the wall ties corrode due to all the moisture trapped inside the cavity, condemn the building?
This is a timely video. My house has a rear extension built in the late 1960s. There are air bricks on the outside wall at ground level but these don’t go all the way through to the inside of the house, but appear to be there to ventilate the cavity. The internal walls get particularly cold where the air bricks are on the outside wall, and so condensation tends to form inside at those spots. Should these external air bricks be sealed?
Don't forget that they may be there to ventilate under your floor(s) in the house. If they are - don't close them off! You can find out if the holes are large enough to take a small camera.. or just break one out and have a look (but have a replacement to hand!)
I have a very similar situation. 60's built extension with cavity, no insulation at all. I have one air brick about 3ft off the ground but it does vent through into the cabinate under the kitchen sink. The air brick isn't ducted so blows into the cavity as well. All seems a bit mad to me, I'm thinking of bricking it up to stop the wind howing through into an already cold room.
I have lived in three rendered houses, two of which were rentals, and had some of the worst mould I have ever seen. Rendering a house or painting the brickwork not only completely destroys its character, but makes it like living inside a huge plastic bag. Houses need to breathe.
Back when people could live below 20C the cavities were all open. Tons of airflow, but not much insulation. Less problem with condensation indoors. Before that it was straight 9 inch with no cavity. Or rock with rubbish infill. Cavity wall insulation is still supposed to sit off the outside brickwork for airflow. Same as roof areas are supposed to have airflow. I remember when they stipulated a 2 inch air gap. And we installed soffit or fascia vents to create that flow. And then tile or ridge vents to exhaust that. Keeping the air moving. Now are you supposed to have no flow. Makes no sense. Not good for the house or the occupants.
The 50mm gap regulation still applies - in roofs its for ventilation, in walls no so, its for water / moisture transfer from outside to in! If moisture can migrate to a cavity or roof void it must be ventilated, if it cannot - it doesn't need ventilation. If you prevent migration (say from a room into a roof space) then the room needs ventilation or damp will occur!
Up untill the early 70s with the advent of cavity insulation all cavities were sealed at roof level and all air bricks wether pantry or floor insulation were chanelled through the cavity with propriety clay sleaves or slate, since cavity insulation appeared cavity insulation has to meet the roof insulation to avoid cold bridging so sealing cavities is a thing of the past.
My parents house built in 1960 has ventilated cavities and under floor space, and has no weep drains or cavity sills so the cavities have to be ventilated otherwise the footings will get wet with the moisture running down. It is a detached property, and when the outside temperature drops below zero C the heating has to be run 24 hours a day to stop the house getting cold. It can't have cavity wall insulation installed, there is too much very random stone in the front and back walls and also due to the issues with no cavity sills at the bottom.
My house built in 1987 has cavity wall insulation and no air bricks. The cavities are open in the loft, but they do not connect to the loft insulation there is at least 150mm all around the edge with no insulation. This is clearly not an accident, they don't connect anywhere. Also the roof line is low so the outer skin of the walls is about two bricks short of reaching ceiling level, so it would be extremely difficult to connect the two sets of insulation. If you did the soffit vents for the loft space would be blocked, hence why it is clear this is part of the design and not a mistake.
Last 2 months i build an extension on my house. I filled our cavity with insulation about 3 years ago, so i was a bit nervous how it looked on the inside after removing some walls (in cold and rainy weather). You dont know how it goes in the cavity, maybe it is a bit wet or dampy or moldy. But it was a perfectly fine, dry insulation, dry bricks, no heaps of insulation flocking together etc. I have to say we do ventilate alot in house and the house is build in 1970, so the bricks and joints are good. I do think if you have a house with bricks and joint that are more porous or broken, you better re do the joins and impregnate the bricks before adding insulation.
I've got air bricks, I always wondered what they were for. They used to let freezing cold air into my kitchen and even froze a nearby water pipe once. Filled every hole with no more gaps and haven't looked back.
Generally good advice but not for houses close to the coast in exposed locations. Salt laden winds will always find weaknesses in walls and water will inevitably penetrate into the cavity . For houses close to the coast and exposed to winds the only safe insulation is internal wall insulation. Cavity wall and external wall insulation should be avoided. But if you are not living close to the coast in an exposed location cavity wall insulation is an excellent and cheap option which does make a big difference - the only problem is the installers are, far too often, cowboys
Could you present a video series designing/managing/building a house built to your best standards. The idealistically built home. Include everything from purchase to plans to permission, consultations with trades. Link videos to why that x is best practice. How much it would cost a normal joe. Could even get a building merchant to sponsor it. Cheers.
If you have caity ties and the cavity gets wet for whatever reason,the insulation would get wet ,cavities where there to keep the internal wall from getting wet,thats why they put air bricks in to circulate air
Great video thank you. Quick question please. My house is a semi-detached with an extension on the side (it was there when i purchased the house) the house has cavity wall insulation all but the extension its not damp but its very cold the insulation companies wont touch it because the cavity is less than 50mm is a closed cell expanding foam any good i have been told that it will make the cavity a solid which yeah it would but will apparently cause damp and more issues it seems that all they want to do is try ans sell me external insulation please any suggestions will be more than welcomed
i spent 25 years injecting wall insulation for miller Pattison owned by Sheffield insulation, ok all the vent we blocked unless a customer noticed and complained about them they stayed blocked floor or room vent , the the top the cavity we just let the insulation overflow into the loft causing all kind of problems, floor vents if they weren't sleeved and when they filled up we just blow air in to them to clean them out , so later on the insulation will just fall down to block them again and start leaving voids where damp will occur, your probably asking why do this simple was pushed by the manager Roy from coventry to do more work, he would say do more i pay you more after all life's all about money hey?
Off topic, but a return to tackling mould with PIVs might be interesting. Now that they’ve been around a while, a short-ish review of the tech would be good. I’m seeing some pieces saying they’re effective, but they drop room temperatures, even with the heated air versions.
@jimw6659 They are just an extractor fan in reverse. They can work well, especially on still days, when the normal wind gusts are not pushing air in though passive vents & then allowing it to flow out again when the gust stops. Everyone goes on about extract fans, but you have to think about the whole airflow. Extracting is fine, but new air has to come in somewhere. If an extract in the bathroom, for examples, is just sucking air from form a trickle vent in a window next to it, then it is doing nothing, just short-cycling. The air has to flow across the room to get the moisture out.
An Insulated cavity should not be closed off at the top, this allows the continuety of the wall insulation to join up with loft inulation with no break between. Close the top and cold bridging occurs.
I live in an early 1960s bungalow, one of many on this area to the same design. They are all prone to mould in the same corner of the bedroom, where there are two outside walls. It's probably because the occupants exhale moisture all night when it's coolest, which condenses in that corner. My neighbour has a vent in that corner, inserted since her bungalow was built. It is only in the external wall; it does not go through to the bedroom. I think it was inserted to try and cure the mould problem. It doesn't. She insists on having the vent left clear (it's on the boundary of my garden) so I leave it clear. Would she be better off blocking it up?
Hi Roger having worked with cavities and insulation on the Architectural Technical side, for many years, it needs to be pointed out the fact Cavity are now wider and interstitial condensation calculation including a dewpoint calcullation needs to be done , when filling a cavity with insulation. I do not agree with you saying cavity needs to be sealed. With the increase in insualtion a flow of air is required through the cavity from the weep holes above the cavity tray and into the loft space, where the insulation shjhould be elither at cieling level or rafter level. A flow of air is important , thick of a chimmney. We can not live in hermetically sealed boxes, nature needs a air balence flow which is calculated!
As a young mechanical building services draughtsman, many moons ago I used to calculate and draw temperature gradients through walls (of various constructon) to see where/if interstitial condensation would occur. I would then advise the architect on a remedy, if required. This was before computer programmes
No, because air-bricks are there for a reason. I have lived in rental houses where the air-bricks had been blocked-up, and all of those houses had damp and mould issues. When I was a lad, I was brought-up in houses which had open fires. We never had any issues with condensation or mildew because there was always a free-flow of air going through the house.
Hi Roger, we have the small ball insulation pumped into our cavity at the front, it was done before we moved in , we’ve had new windows fitted but every year we get black mould growing around the window reveals and above the rsj. Do you think it would work if we sucked out the insulation with a hoover, someone suggested it’s causing a damp bridge? Cheers
You should probably clarify that viewers need to first know if their house is a masonry cavity wall or a timber frame with block outer leaf. If they go around sealing weep vents on a timber frame house, they'll be in trouble (unless they know the specification of the breather membrane - but still risky). Sealing cavities to the roof, around openings and at boundaries is required for limiting spread of fire within the cavity.
I have a squirrel (or similar) in my bungalow loft space chewing the alarm cables. I have UPVC soffits and fascias and can’t see any gaps. How do I discover where he got in please?
Any advice for a house built in 1866 and only has a thumbnail cavity? The house is painfully cold, even after new roof fitting and double glazing replaced.
Not sure u want kill airflow though the cavities, as it’s a tried and tested way of preventing moisture build up , which could cause problems with damp and eventually rot ( in timbers ) capping the top at the eaves makes sense but sealing up or removing the air bricks at low level, I’m not so sure,trapped air is a great insulator ( as roger says ) but trapped moisture laden air in the cavity is only gonna lead to problems further down the line I reckon , uve gotta somehow come to a compromise between the two scenarios insulation but without introducing a damp issue and airflow whilst trying to reduce heat loss , it’s tricky , especially in a retro fit scenario ( with no or virtually no access to the cavity .)cavity wall insulation can cause its own problems also and any rockwool type of insulation in the cavity is a complete no no ( if it gets damp it will definitely cause damp , especially at low level as it starts to slump under its own increasing wet weight) and the micro beads stop the airflow at low level . Like I said it’s a problem on older properties, not so for new build if built correctly to the regs ( although we all know that don’t always happen 🫤)
Interesting. I’ve never known a cavity wall to be blocked off at the top. I’d assumed the reason was, there is no significant air flow, as the bottom of the cavity is airtight, but it still allows any excess moisture to rise to the top and disappear in your vented loft. Your taped PIR board would be pressed tight against the inner blockwork, meaning the insulation properties would be intact. I don’t like the idea of sealing off the cavity.
The best stuff for cavity insulation now is extratherm with the plastic front brilliant stuff always leave a air gap between insulation for ventilation. All the full fill stuff is absolutely shite.
Your videos are always interesting Roger! I have air bricks that are below floor level, but have a concrete floor (late 1970s bungalow). Does this mean the floor is in fact block and beam, and there is are space underneath it? Cheers
Dutch here. In about 1978, our neighbors took out the wooden floor and poured concrete on sand. Then we got rising humidity in our living room. In 1980 my father took out (with an other side neighbor) our wooden floor, 4 by 9m, and drilled holes to put chemicals in them. Then he installed concrete beams and concrete "breads" between them and filled it on top so that it is flat. Then he installed yellow airing bricks that ventilate the crawl space under the floor. Two on the front sidewalk side and on the back yard side. Problem solved since 1980. Also in this vid you see the area between the bricks and the window being sealed with silicone but that area must stay open. My parents house is from 1905 and the window frame is from 1905 and it is still okay. The bricks do not touch the window frame. I also saw it in a building school vid that even nowadays the young people learn to keep that open for ventilation. In the vid the teacher says that rain will not come in but the normal moister must be able to escape.
someone put a concrete floor in my kitchen which blocks the airflow which used to go under floors from front of house to back. i hope they put in air pipes but i doubt it
My house - 1970's concrete lower floor, its a 1 off house. The odd thing it has no weep vents. being honest I think the house seems quite condensated? Should I have weep vents from the cavity to the outside? :(
I have ventilation bricks in my wall (built 1929) which are definitely above floor level and definitely don't go through to the room. I know this because I had damp coming through my internal wall and on inspection I found that looking through the ventilation brick is was block up with sand. I had to remove brick and dig out all of the sand (god knows where it all came from). All that was on the other side was the internal wall where all of the damp was. The damp wall has now dried out.
Many years ago we got cavity wall insulation , it was a government thing ( seemingly ) where this was pumped into the cavity ans all air bricks are sealed with this gel … my house is 30 years old now with no problems I’m aware of but I often wondered if this was the right thing to do .. any comments . . ?
Trapping movement of air more importantly. I'm not sure but I think cavity convection is a thing? Maybe you can clarify this, if true or not, I am thinking of getting the party walls gap filled. I think convection is the reason why feathers are more insulating in a jacket than just air sacks, but maybe it's radiation. On a further point, in many houses we need a bit of heat loss to dry that skin out, most house brick don't last long if they become damp.
Well Roger, as a long time fan of 'Bisby News' :-) i would have to query your assertion that air (whether moisture laden or not) from the cavity could lead to an appreciable amount of condensation in the roof space .. I have no evidence to the contrary as such, but roof spaces generally have a reasonable air-flow for lots of reasons .. so if one were to see a lot of condensation in the roof space my first thought would be to check the roof space ventilation (as we know that some folk stuff so much rockwool right into the eaves that natural ventilation is diminished) .. but carry on Sir, as you put out some great info and there's often a talking point to get our teeth into :-)
In my new place to moved into back in May, there’s been a persistent problem with hotspots on the ceiling for condensation and mould build up, there is even a moist/damp patch of wall by the bedroom window, surveyors from the council say either it’s a “slow leak” (why and where from?!) and/or to do with the cavity wall. In rear of the property (I live in a 70s build bungalow) there are two brick air vents which appear to have been filled with expanding foam by the previous tenant! Do I unblock these or not?? Insulation in the loft apparently is sufficient but around the eaves is going to be further inspected by roofers by removing a couple tiles. The condensation and mould appears in bedroom, bathroom and kitchen, and yes I have the trickle vents open 24/7 and open windows daily, even for an hour or so during winter months.
i use a £15 infrared gun thermometer to dind the cold areas in walls and ceilings - they were in the top 6 inches of the walls, i kingspanned them during roof repairs
Hi Rodger, thanks for another informative video, we live in a bungalow with these air bricks west facing front and back east. When we moved in most were covered up, I removed all and we get lots of mould on the west side, should I cover all and the loft gaps? George Staszak Mr Combi 🤩
Regulations for brick or block clad timber framed buildings require cavity ventilation top and bottom. That said, I do wonder if what they require is sufficient to make much difference. There is a huge difference between a rendered block wall and a brick wall. Especially with hard bricks, driven rain can actually spurt into the cavity. With wide insulated cavities I believe there have been practically no issues, and any probably poorly fitted cavity trays. Retired Architect. ps, when I started, before sealing the top of a cavity, the builder would go round with a long 2x1” and knock off any snots on wall ties.
@@markthomasson5077 In Australia our bricklayers hose the cavities out every afternoon, they also leave clean outs at the dpc and those that out every day. I don’t see the English brickies do that.
Pretty sure my double air bricks (double the height of a brick) vent both the sub floor and the wall cavity - I live in a 1960's bungalow. I've always wondered if the air from the air bricks is cooling the cavity and therefor providing heat loss.
You don't dry your clothes after washing by putting them in a closed plastic bag, you let air movement (draft or wind) on them to dry them out. So how does sealing the cavity help get rid of any moisture build up, be it from penetrating water from rain on the ouside courses of brick, or inside from a leak of some kind. Once you get moisture laden air you have condensation somewhere. Lack of air movement in houses is one reason we are seeing so many pictures and click bait stories of black mold. I love seeing these pictures of huge horrible mold in houses - basically means they are too lazy to clean it off !
This is also my logic, better blowing into the loft than soaking into the internal skin? Or mold filling the cavity. Perhaps this is in reference to new builds. Either way, often these short 3m videos leave more questions than answers. Rogers longer form content is much better.
If you have alot of moisture in you cavity there are propably things you can do first to avoid that. But ofcourse you can live in a area or in a house were cavity insulation is just not an option.
Black mould is a PITA. We have all upstairs windows left on vent 24/7. The bathroom and kitchen have extractors venting to outside and I clean the grilles and duct once a year (doesn't need anymore than that it as even then they aren't particularly dirty). I open all windows in the house for 10-15 mins twice a day. There is a 'healthy' draught unser the front door too. The children have a moisture absorber (unibond ring shaped model) in their bedrooms too. Probably only removing trace amounts of moisture each and only a portion of any excess when their blinds are closed which will almost seal off the vented window area. We still get black mould growing in the bathroom on the walls and ceiling and a bit in other rooms around the window reveals. We hit it with a dedicated black mould remover every so often (tried both HG and the Bang brands). It always comes back. Victorian house with no obvious damp issues - we had areas that were picked up when we bought the house treated and that seems to have been good for the ast 19 years - skirtings, plaster, paint no problem at all. Central heating to every room although generally set at 18 unless we're feeling the chill and then we go up to 19.5. Not sure what is going on but it's annoying. Not huge patches of the stuff and we're all relatively young, fit and healthy so not at major risk from it. Be nice to get rid once and for all though.
I've got an odd internal cavity vent (white plastic louvered thing) on the internal wall of a cavity wall situation. The gable end is north-facing and gets cold bridging along the bottom sometimes causing condensation (the condensation pattern seems like it follows the mortar detritus etc in the cavity) , and I wondered of this was a 'fake' solution to that, or if it was where they put in some fibreglass insulation (which is in there) and never closed it back up properly. It's very strange.
@@chapman9230 Thanks for the reply. 👍There's no open fire in the whole place. I can only assume it was either to placate the previous resident/s about the condensation or to install some fibreglass cavity insulation, it just seems very odd. It doesn't go through to the outside wall and isn't sleeved, when you pull it off to reveal the hole (5/6 inches across) you can see the insulation so maybe it was to do with installing that, but I haven't yet come to a satisfactory conclusion about it. For example someone suggested it might have been for a tumble dryer exhaust, but as it doesn't go outside and is in a position where you would never put an exhaust/dryer I have ruled that one out.
@@thesunreportI suspect it used to go to outside and be sleeved as a vent for the room. But then when cavity wall insulation was retro fitted they bricked up the outside vent and just left the inside with the vent face.
I've started seeing quite a few Cavity Wall Insulation Removal Vans in my area recently. Why might that be Rog? Not being facetious. After a recent outbreak of dry rot in a suspended timber floor I wouldn't dream of bunging up the cavity wall in my old 1930's semi. Horses for Courses? I'm also up North, tis Grim.
@@chrisallen5548but it wont completely will it. In the long winter months with any driven rain and even condensation, that cavity would remain damp and begin to mould up on any smooth surfaces in particular. I would personally leave the top of the cavity open and insulate with something that doesn’t hold moisture. That is unless you can, with absolute certainty, prevent any ingress, apply lateral vapour control and seal the cavity entirely with no airflow. Borderline impossible.
I had a call, after cavity wall insulation fitted, mould and damp build up. Now the FB damp & condensation group would be jumping all over this as they see cavity insulation as the devils own work. I actually posted my thoughts & solution as below & got banned! What it was, was the air-vents fitted in most rooms, had not been sealed where they go through the cavity. House built before we had plastic vent liners. So the vent hole also got filled with insulation thus blocked the vent. Simple solution, tap out the old plaster vent and fill around the cavity with squirty foam, to hold the insulation back. Fit a new plastic vent.
I would argue that each building design is different so a 1 size fit's all approach doesn't work. Some houses need the airflow/cavity regardless. Filling it will just cause issues. The building next door might be similar but is ok with cavity filled with insulation. Materials used, quality of the job will all effect the outcome.
No. Timber frame cavities must be ventilated at high and low level at each storey with perpend vents. I’m surprised and disappointed that this wasn’t mentioned as timbers frame is the predominant house construction type nowadays.
Ah so I could trying to block the cavity left open in the loft ? I have them open and get the odd rat every now and again coming it. God knows from where but keeping it in the wall in better than the loft.
We've got a single storey extension with cavity wall insulation whereas the rest of the house hasn't, the extension in theory should be the warmest part of the house BUT the extension has vented sofit, the cavity isn't closed at the top and the interior walls are dot dabbed so air leakage negates the insulation, if I ever can afford to have my own house built I've got all the spec planned out 😂
Nothing new? I have original ventilation blocks in my 200 year old "solid " stone walls. Not through but on outside of walls only . Walls are usual 600 mm thick of two skins with rubble fill. It is often said that if you can ventilate somewhere then do it, even if only trickle
Im self building a house with partial fill cavity wall but no one seems to close off the top of the cavity in our area. Since face brick outer skin lets through a lot of wind driven rain, if i close off the top how will this escape, both the water pooling at the bottom of the cavity, and the condensation from it trying to evaporate? The bottom of the empty cavity is 300mm below outside ground level, which is clay soil so weep holes wouldnt work, they'd be blocked or letting it in. I'm going to apply stormdry masonry cream to minimise the water ingress.
Well done, very well explained, I've been trying to tell people the exact same thing but there all super intelligent builders and don't want to learn any more.
No I lived in a coal board house from the 1962 up to 2014 and I never had any cavity wall insulation fitted and we had no damp and there was air bricks fitted to every room in the house and they did there job even at winter kept open ok
Do we block up all the weep holes as well then? If ever there was a waste of time it was weep holes. The Germans don't use them so why do we? When cavities were ventilated we didn't have half the problems we do now. We have to fit cavity trays halve way up the building, why? All that plastic just adds to condensation. As for closing the cavity at plate height, (loft) haven't done that for years.
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So many times people say... "Yeah but It's meant to breathe" ... 😂😂😂 Seal-off your cavity, seal everywhere with damp membranes, seal the windows and doors well, DO NOT ALLOW ANYTHING TO "Breathe" 😂 use dehumidifier in your homes people. Toilets and kitchen need good extractor fans, and thats it. Dont let your walls and exterior fittings breathe 😂
Hi Roger, up here in Scotland for the last 40 - 50 years the majority of new build houses have been timber kit construction where it is essential that the cavity is ventilated. The regulations state that ''Cavities should be vented to the outside air by installing ventilators with at least 300mm2 free opening area at 1.2m maximum centres." This is normally achieved by installing ventilation cassettes similar to weep vents but full hight of the brick (65mm). The cavity fire barriers should also be taken into account with the placement of ventilation cassettes each side of the barrier. This ensures that each fire compartment within the cavity is properly ventilated with ventilation cassettes at the bottom and top of each compartment. Why don't you do a collaboration video with someone who is fully up to speed with the Scottish regulations and practices. I'm sure your many Scottish subscribers will appreciate it. Good videos. Your plumbing ones in particular are excellent.
I should have added that we do use cavity insulation but it is now generally a solid sheet installation that doesn't completely close the cavity. An air gap is always maintained to provide the ventilation.
Cracking insight into a mysterious world for most people, Roger. Crisp, to the point, clear and accurate. What more could we want. Cheers.
Bit of extra history I discovered as a building surveyor: large air bricks were often placed above the DPC level to ventilate larders or pantries in houses built before the widespread use of fridges. You can normally identify these 1. Where they directly align with a large larder or pantry and 2. If it was on the north most facing side of the house out of direct sun light. Roger is right most of these ‘wall airbricks’ are to ventilate a room though.
my Mum had a "pantry" under the stairs before the advent of electric fridges, comprising of a zink screen in front of an air brick and food sat on a marble slab, one tuesday she had a nasty shock and chucked half a joint of beef crawling with maggotts and blueflies, that was dinner, bastards.
My 1911 terrace has lime mortared cavity brick walls. The cavity is ventillated externally by huge cast iron vents a the top and bottom, plus gaps into the cavity above all the sash window frames. After 100+ years the walls are beautifully stright with apparently no issues with corrosion of the wall ties, but I hate to think what could happen if I messed with the cavity ventilation in any way.
When I was an apprentice, regs were just introducing insulation into 50mm cavities! My mentor always moaned about it bridging the cavity and reducing air circulation and the batts making rags on the ties causing damp.
The price per 1000 didn't go up though, I think that was his main gripe!
I was always stunned by the sheer simplicity of cavity wall insulation sales folk. They'd knock on my door and ask if I want it, I'd tell them it's a Victorian house - with solid brick walls. They'd say 'oh'... and then go next door, and enxt door to that etc. In a terrace of houses exactly the same, getting the same answer each time.
They have now moved onto the highly toxic and flamable external insulation. So they're having to be told what a conservation area is by everyone that answers.
I'm in a conservation area and I'm having external wall insulation. It was approved with no conditions by the council. It would only be if the parish council are staunch traditionalists or if the house is listed that you might have any issue.
It would only take one, probably elderly, houseowner, who doesn't know/understand they have single skin walls, to say yes. Then they could turn up, drill a few holes in the walls, make some noise and pack up.
Flammable are you sure
@@peterthebricky
Just looked one up, has Class E fire rating, which means it is combustable and has a high contributes to the fire.
Edit; The class E was a polystyrene based one.
I can see Kingspan have some class C and Rockwool has an A1 - so if you are getting external insulation, go for something that seems fireproof like Rockwool.
Housing designed with vented cavities ( 1920s,30, 40, 50, ) are best left vented. The cavities are open at wall plates for ventilation of roof timbers and timber floors.
This method of construction was practical, to prevent dry rot.
Okay... I am an Engineer (old school), who is in the later stages of building a timber frame passive house. I have a rendered block outer leaf with 50mm cavity. the timber frame has a semi permeable foil/fabric layer onto 9mm OSB sheathing, which in turn nailed to 235mm inner leaf timber stud work. The top of the cavity wall is closed off with fire socks.
The semi permeable membrane works on an "Osmosis" method where it allows residual moisture content in the frame to escape into the cavity. If that cavity is fully closed and saturated with moisture, like after having heavy driving rain then sun heating the wall, creating high humidity, this effect will be diminished.
Also by having cavity trays at DPC level and above Lintels, there are weep vents at 900mm intervals, so there will be air movement to a degree. The fire socks around the roof line will stop air to the attic space, and also fire if it does happen. I believe that having a closed off cavity will eventually impact on the timber frame in the future. Because of my fears, probably unfounded, I will be painting the render with ProPerla paint when the weather warms up. Apparently, hydrophobic paint is the way to go nowadays.
@adamsweet3587 could you not install a soffit/fascia vent so any moisture goes outside and you maintain the firestop..? I would also paint the render...
How does cavity 'saturate' with moisture after heavy rain? What is the point of building an external wall if this occurs - bricks absorb / pass water through VERY slowly so unless under water or direct heavy rain for weeks and weeks, its not going to happen! If you are building with an internal breathable skin then that MUST be ventilated on its outer face - the design is not correct if not, you are mixing methods and not in a good way!
As long as you're weep vents are 65mm high and you have them at 900 centres above and below any fire socks and at dpc level at the ground, this should be sufficient to properly vent the cavity. Here in Scotland for timber frame construction, the regs require cavity vents of at least 300mm2 every 1200mm. You should get more than that if your vents are at 900 centres.
@@kawazukisoddbits2717 If you have a closed cavity and have a damp inner side of the outer leaf, and after a period of driven rain, the eventual sun will initial warm that wall to create a more humid environment, until the wall outside dries, to then pull back the moisture to the outside. The levels here maybe very small and will not affect the inner leaf and I am probably being overly too critical. Traditionally cavities were open at the top and roof eaves had ventilation either in the soffits or as vent bars sitting on top of the fascia boards(which the tile sat on), so you had a vented loft space. My house is on a hill (in Cornwall), exposed, South facing, and the South West weather fronts do push hard on my facing walls.
@@WilliamBell-tj9sq Yes, I do have weep vents at DPC and Lintel levels, so when my exposed house experiences high winds, which it does, it will force air from the exposed side around to the other side which will be at lower air pressure. I am probably being overly critical of my situation.
Here in Australia the top of the cavity and the cavity itself are left open to vent the cooler under floor air. This keeps the house cooler in summer and keeps the underfloor drier.
yeah a lot of people forget about pre AC construction in hot environments
You wouldn't be doing that in Shetland mate lol!
I have a 1928 built detached house with a cavity. The parlour was built with a suspended floor. There are air bricks front and rear, wind blows right through. However, the cavity has openings below floor level so wind blows up the unfilled cavity. There are air bricks level with the top of the 1st floor windows, these are unsleeved with cast iron sliding vents. The cavity is open at loft level. Effectively I have a single skin house as the walls are cooled (but dry) by cold wind blowing through. The walls inside are really cold. I have a lot to sort out!
Hi Roger, At Last...!!! It took me forever to find a video on cavities. It seems everyone talks about window reveals and door reveals, but you are the first I can find to talk about the top of the cavity. Thank you for clearing this up. There is not much information on the top (eaves) of the cavity and how it should be sealed. Also it seems that not many of the eaves I have seen on older houses seem to be sealed in the construction. Maybe an oversight or just lazy builders. Thanks Roger and the Skill Builder team...
In a brick/block built building with a cavity that is fully sealed, how does moisture from driving rain seeping into the cavity escape?
If the cavity warms up and has moisture, shouldn't there be somewhere for the moisture to go?
Could a fully sealed cavity with no air flow cause dry rot?
Does 'Rockwool' style cavity insulation allow air flow when the cavity is fully filled with it? Does it soak up and hold moisture or does it transfer it to the internal skin?
These are the discussions I have on site consistently over the years and everyone has a different view.
Personally, as a Bricklayer, I never seal the cavity at the top, I don't insert air bricks to the cavity and I prefer to use Rockwool type insulation when I can. I've never experienced any issues but I still don't know if that's the right way to go or not after more than 40 years on the trowel.
It seems that some people confuse ventilation, draining and breathability. In the east of England where i now live most buildings up to 1960 are built with solid walls because it's a dry 2:49 climate and the bricks were low poroucitty with lime mortar; hence no need for cavities. There's no point allowing wet cold air to circulate against the internal skin which is transmitting moisture from the inside thus causing condensation which shows as damp on the bottom of the inside wall.
Very interesting.. I think that’s my problem.. thanks for the insight..👍
Filling a cavity with insulation bridges the cavity and allows water to track onto the internal wall and is particularly poor building practice.
Have you been living under a rock for the past 30 odd yrs? Fully filled cavities have been used and APPROVED for use in this time! Bad workmanship is the cause of damp penetration!
@ It is like putting a sponge inside the cavity retaining moisture . It bridges the cavity and draws water across the dry interior skin. It also promotes corrosion of the wall ties. Unless the exterior face of the wall is sealed with a properly sealed foil and reasonable gap maintained water will track across. It is such a stupid idea approved by officials that have had a mind fart.
It has never been legal in my country. We frankly still have our brains turned on.
@ It cannot work, you are putting a sponge inside the cavity and tracking moisture to the dry skin. You are also jeopardising the structural integrity of the building by creating a moisture soak at every wall tie encouraging them to corrode. It could work with foil faced insulation but a cavity should still be maintained. Whoever approved that 30 years ago was having a brain fart.
It’s not legal where I come from we still have our brains turned on. Seriously it is absolutely nuts, and fixing it with a paint on sealant is bs too. It’s poor building practice.
@davidconnolly7346 not arguing but where are you from. I'm in essex UK, I've laid bricks since 1986 with full fill insulation in 95% of the cavity work. I've yet to have a comeback. Modern full fill bats are water repellent but the older stuff not so much
The primary role of the cavity is to waterproof the building not provide a location for insulation. A way better method if you want additional insulation is brick veneer with the insulation within the interior timber wall. We leave our cavities open in Australia. We get so 3:04 much rainfall too. Cavities get a lot of water inside them, they also need ventilation to dry them out. It’s been working for 100’s of years.
What do you do in England when all the wall ties corrode due to all the moisture trapped inside the cavity, condemn the building?
Thanks Roger, very straight forward and informative ! Great balance and varied comments below too of course 1
This is a timely video. My house has a rear extension built in the late 1960s. There are air bricks on the outside wall at ground level but these don’t go all the way through to the inside of the house, but appear to be there to ventilate the cavity. The internal walls get particularly cold where the air bricks are on the outside wall, and so condensation tends to form inside at those spots. Should these external air bricks be sealed?
Don't forget that they may be there to ventilate under your floor(s) in the house. If they are - don't close them off! You can find out if the holes are large enough to take a small camera.. or just break one out and have a look (but have a replacement to hand!)
I have a very similar situation. 60's built extension with cavity, no insulation at all. I have one air brick about 3ft off the ground but it does vent through into the cabinate under the kitchen sink. The air brick isn't ducted so blows into the cavity as well. All seems a bit mad to me, I'm thinking of bricking it up to stop the wind howing through into an already cold room.
If you have wooden floors down stairs the vent are for air flow under the floor
I have lived in three rendered houses, two of which were rentals, and had some of the worst mould I have ever seen.
Rendering a house or painting the brickwork not only completely destroys its character, but makes it like living inside a huge plastic bag.
Houses need to breathe.
Back when people could live below 20C the cavities were all open. Tons of airflow, but not much insulation. Less problem with condensation indoors. Before that it was straight 9 inch with no cavity. Or rock with rubbish infill. Cavity wall insulation is still supposed to sit off the outside brickwork for airflow. Same as roof areas are supposed to have airflow. I remember when they stipulated a 2 inch air gap. And we installed soffit or fascia vents to create that flow. And then tile or ridge vents to exhaust that. Keeping the air moving. Now are you supposed to have no flow. Makes no sense. Not good for the house or the occupants.
The 50mm gap regulation still applies - in roofs its for ventilation, in walls no so, its for water / moisture transfer from outside to in! If moisture can migrate to a cavity or roof void it must be ventilated, if it cannot - it doesn't need ventilation. If you prevent migration (say from a room into a roof space) then the room needs ventilation or damp will occur!
Up untill the early 70s with the advent of cavity insulation all cavities were sealed at roof level and all air bricks wether pantry or floor insulation were chanelled through the cavity with propriety clay sleaves or slate, since cavity insulation appeared cavity insulation has to meet the roof insulation to avoid cold bridging so sealing cavities is a thing of the past.
My parents house built in 1960 has ventilated cavities and under floor space, and has no weep drains or cavity sills so the cavities have to be ventilated otherwise the footings will get wet with the moisture running down. It is a detached property, and when the outside temperature drops below zero C the heating has to be run 24 hours a day to stop the house getting cold. It can't have cavity wall insulation installed, there is too much very random stone in the front and back walls and also due to the issues with no cavity sills at the bottom.
My house built in 1987 has cavity wall insulation and no air bricks. The cavities are open in the loft, but they do not connect to the loft insulation there is at least 150mm all around the edge with no insulation. This is clearly not an accident, they don't connect anywhere. Also the roof line is low so the outer skin of the walls is about two bricks short of reaching ceiling level, so it would be extremely difficult to connect the two sets of insulation. If you did the soffit vents for the loft space would be blocked, hence why it is clear this is part of the design and not a mistake.
Our 1930s house has a cavity that is unsealed at roof level.
@@bricklayersworldwithandy6277 thank you someone who knows what they're talking about.
Last 2 months i build an extension on my house. I filled our cavity with insulation about 3 years ago, so i was a bit nervous how it looked on the inside after removing some walls (in cold and rainy weather). You dont know how it goes in the cavity, maybe it is a bit wet or dampy or moldy. But it was a perfectly fine, dry insulation, dry bricks, no heaps of insulation flocking together etc.
I have to say we do ventilate alot in house and the house is build in 1970, so the bricks and joints are good.
I do think if you have a house with bricks and joint that are more porous or broken, you better re do the joins and impregnate the bricks before adding insulation.
I've got air bricks, I always wondered what they were for. They used to let freezing cold air into my kitchen and even froze a nearby water pipe once. Filled every hole with no more gaps and haven't looked back.
if the rain/damp is driven into an empty cavity how does it evaporate away if all sealed in?
The same way it got in
In modern buildings, that is where wall weep vents will come in
It condenses on the inner face of the external leaf and gravity brings the water droplets to the weep tray and out the front
Full fill on a new build wall is ok when it's also being cladded. But if it's not I'll be sticking with minimum 50mm air gap
Generally good advice but not for houses close to the coast in exposed locations. Salt laden winds will always find weaknesses in walls and water will inevitably penetrate into the cavity . For houses close to the coast and exposed to winds the only safe insulation is internal wall insulation. Cavity wall and external wall insulation should be avoided.
But if you are not living close to the coast in an exposed location cavity wall insulation is an excellent and cheap option which does make a big difference - the only problem is the installers are, far too often, cowboys
yes, it depends on the weather where the house is
If a cavity wall doesn’t need airflow, why doe we need airflow underneath floors/joists?
Could you present a video series designing/managing/building a house built to your best standards. The idealistically built home. Include everything from purchase to plans to permission, consultations with trades. Link videos to why that x is best practice. How much it would cost a normal joe. Could even get a building merchant to sponsor it.
Cheers.
Great work, Roger
If you have caity ties and the cavity gets wet for whatever reason,the insulation would get wet ,cavities where there to keep the internal wall from getting wet,thats why they put air bricks in to circulate air
My house does not have a liner in when i looked through the air brick vents. It is a cavity wall house, Is this wrong? House is 30 yrs old.
Great video thank you.
Quick question please. My house is a semi-detached with an extension on the side (it was there when i purchased the house) the house has cavity wall insulation all but the extension its not damp but its very cold the insulation companies wont touch it because the cavity is less than 50mm is a closed cell expanding foam any good i have been told that it will make the cavity a solid which yeah it would but will apparently cause damp and more issues it seems that all they want to do is try ans sell me external insulation please any suggestions will be more than welcomed
Hi Roger If the cavity is sealed , and water penetrates through the outside brick . What happens to that water if it can’t escape . ? Kind regards 🙏
i spent 25 years injecting wall insulation for miller Pattison owned by Sheffield insulation, ok all the vent we blocked unless a customer noticed and complained about them they stayed blocked floor or room vent , the the top the cavity we just let the insulation overflow into the loft causing all kind of problems, floor vents if they weren't sleeved and when they filled up we just blow air in to them to clean them out , so later on the insulation will just fall down to block them again and start leaving voids where damp will occur, your probably asking why do this simple was pushed by the manager Roy from coventry to do more work, he would say do more i pay you more after all life's all about money hey?
Off topic, but a return to tackling mould with PIVs might be interesting. Now that they’ve been around a while, a short-ish review of the tech would be good. I’m seeing some pieces saying they’re effective, but they drop room temperatures, even with the heated air versions.
@jimw6659 They are just an extractor fan in reverse. They can work well, especially on still days, when the normal wind gusts are not pushing air in though passive vents & then allowing it to flow out again when the gust stops.
Everyone goes on about extract fans, but you have to think about the whole airflow. Extracting is fine, but new air has to come in somewhere.
If an extract in the bathroom, for examples, is just sucking air from form a trickle vent in a window next to it, then it is doing nothing, just short-cycling. The air has to flow across the room to get the moisture out.
An Insulated cavity should not be
closed off at the top, this allows the continuety of the wall insulation to join up with loft inulation with no break between.
Close the top and cold bridging occurs.
Not if you close it with an insulator
it depends on the weather where the house is, is there a wet wind blowing onto the wall?
I live in an early 1960s bungalow, one of many on this area to the same design. They are all prone to mould in the same corner of the bedroom, where there are two outside walls. It's probably because the occupants exhale moisture all night when it's coolest, which condenses in that corner.
My neighbour has a vent in that corner, inserted since her bungalow was built. It is only in the external wall; it does not go through to the bedroom. I think it was inserted to try and cure the mould problem. It doesn't.
She insists on having the vent left clear (it's on the boundary of my garden) so I leave it clear. Would she be better off blocking it up?
Hi Roger having worked with cavities and insulation on the Architectural Technical side, for many years, it needs to be pointed out the fact Cavity are now wider and interstitial condensation calculation including a dewpoint calcullation needs to be done , when filling a cavity with insulation. I do not agree with you saying cavity needs to be sealed. With the increase in insualtion a flow of air is required through the cavity from the weep holes above the cavity tray and into the loft space, where the insulation shjhould be elither at cieling level or rafter level. A flow of air is important , thick of a chimmney. We can not live in hermetically sealed boxes, nature needs a air balence flow which is calculated!
As a young mechanical building services draughtsman, many moons ago I used to calculate and draw temperature gradients through walls (of various constructon) to see where/if interstitial condensation would occur. I would then advise the architect on a remedy, if required. This was before computer programmes
@@MarkJones-ji8fd Can you calculate the amount of water that tracks across the cavity when it’s full of insulation and not being ventilated?
@davidconnolly7346 no, only where in the wall construction condensation was likely to occur
So you should block up air bricks if you have cavity walls?
No, because air-bricks are there for a reason. I have lived in rental houses where the air-bricks had been blocked-up, and all of those houses had damp and mould issues.
When I was a lad, I was brought-up in houses which had open fires. We never had any issues with condensation or mildew because there was always a free-flow of air going through the house.
@ so why is he saying to block them up then?
@@GeorgeAusters He didn't. He said that the cavity should be sealed.
Hi Roger, we have the small ball insulation pumped into our cavity at the front, it was done before we moved in , we’ve had new windows fitted but every year we get black mould growing around the window reveals and above the rsj. Do you think it would work if we sucked out the insulation with a hoover, someone suggested it’s causing a damp bridge? Cheers
You should probably clarify that viewers need to first know if their house is a masonry cavity wall or a timber frame with block outer leaf. If they go around sealing weep vents on a timber frame house, they'll be in trouble (unless they know the specification of the breather membrane - but still risky).
Sealing cavities to the roof, around openings and at boundaries is required for limiting spread of fire within the cavity.
This is very helpful, thank you so much. 🙂
I have a squirrel (or similar) in my bungalow loft space chewing the alarm cables. I have UPVC soffits and fascias and can’t see any gaps. How do I discover where he got in please?
Any advice for a house built in 1866 and only has a thumbnail cavity? The house is painfully cold, even after new roof fitting and double glazing replaced.
Not sure u want kill airflow though the cavities, as it’s a tried and tested way of preventing moisture build up , which could cause problems with damp and eventually rot ( in timbers ) capping the top at the eaves makes sense but sealing up or removing the air bricks at low level, I’m not so sure,trapped air is a great insulator ( as roger says ) but trapped moisture laden air in the cavity is only gonna lead to problems further down the line I reckon , uve gotta somehow come to a compromise between the two scenarios insulation but without introducing a damp issue and airflow whilst trying to reduce heat loss , it’s tricky , especially in a retro fit scenario ( with no or virtually no access to the cavity .)cavity wall insulation can cause its own problems also and any rockwool type of insulation in the cavity is a complete no no ( if it gets damp it will definitely cause damp , especially at low level as it starts to slump under its own increasing wet weight) and the micro beads stop the airflow at low level . Like I said it’s a problem on older properties, not so for new build if built correctly to the regs ( although we all know that don’t always happen 🫤)
Interesting. I’ve never known a cavity wall to be blocked off at the top. I’d assumed the reason was, there is no significant air flow, as the bottom of the cavity is airtight, but it still allows any excess moisture to rise to the top and disappear in your vented loft. Your taped PIR board would be pressed tight against the inner blockwork, meaning the insulation properties would be intact. I don’t like the idea of sealing off the cavity.
The best stuff for cavity insulation now is extratherm with the plastic front brilliant stuff always leave a air gap between insulation for ventilation. All the full fill stuff is absolutely shite.
Your videos are always interesting Roger! I have air bricks that are below floor level, but have a concrete floor (late 1970s bungalow). Does this mean the floor is in fact block and beam, and there is are space underneath it? Cheers
You can have both, one room in concrete, the other not. Why, i have no idea.
Or it was built with suspended timber floors but filled in and concreted at a later date
Dutch here. In about 1978, our neighbors took out the wooden floor and poured concrete on sand. Then we got rising humidity in our living room. In 1980 my father took out (with an other side neighbor) our wooden floor, 4 by 9m, and drilled holes to put chemicals in them. Then he installed concrete beams and concrete "breads" between them and filled it on top so that it is flat. Then he installed yellow airing bricks that ventilate the crawl space under the floor. Two on the front sidewalk side and on the back yard side. Problem solved since 1980. Also in this vid you see the area between the bricks and the window being sealed with silicone but that area must stay open. My parents house is from 1905 and the window frame is from 1905 and it is still okay. The bricks do not touch the window frame. I also saw it in a building school vid that even nowadays the young people learn to keep that open for ventilation. In the vid the teacher says that rain will not come in but the normal moister must be able to escape.
someone put a concrete floor in my kitchen which blocks the airflow which used to go under floors from front of house to back. i hope they put in air pipes but i doubt it
My house - 1970's concrete lower floor, its a 1 off house. The odd thing it has no weep vents. being honest I think the house seems quite condensated? Should I have weep vents from the cavity to the outside? :(
Good explanation of cavity walls.
Taught as an apprentice to close off the cavity.
I have ventilation bricks in my wall (built 1929) which are definitely above floor level and definitely don't go through to the room. I know this because I had damp coming through my internal wall and on inspection I found that looking through the ventilation brick is was block up with sand. I had to remove brick and dig out all of the sand (god knows where it all came from). All that was on the other side was the internal wall where all of the damp was. The damp wall has now dried out.
a lot of vents were put in to provide air flow for a fireplace, long gone !!
Many years ago we got cavity wall insulation , it was a government thing ( seemingly ) where this was pumped into the cavity ans all air bricks are sealed with this gel … my house is 30 years old now with no problems I’m aware of but I often wondered if this was the right thing to do .. any comments . . ?
Trapping movement of air more importantly. I'm not sure but I think cavity convection is a thing? Maybe you can clarify this, if true or not, I am thinking of getting the party walls gap filled. I think convection is the reason why feathers are more insulating in a jacket than just air sacks, but maybe it's radiation.
On a further point, in many houses we need a bit of heat loss to dry that skin out, most house brick don't last long if they become damp.
Well Roger, as a long time fan of 'Bisby News' :-) i would have to query your assertion that air (whether moisture laden or not) from the cavity could lead to an appreciable amount of condensation in the roof space .. I have no evidence to the contrary as such, but roof spaces generally have a reasonable air-flow for lots of reasons .. so if one were to see a lot of condensation in the roof space my first thought would be to check the roof space ventilation (as we know that some folk stuff so much rockwool right into the eaves that natural ventilation is diminished) ..
but carry on Sir, as you put out some great info and there's often a talking point to get our teeth into :-)
I don't have a liner that goes through the cavity on my living room air brick so the air can go into the cavity. I have cavity insulation.
In my new place to moved into back in May, there’s been a persistent problem with hotspots on the ceiling for condensation and mould build up, there is even a moist/damp patch of wall by the bedroom window, surveyors from the council say either it’s a “slow leak” (why and where from?!) and/or to do with the cavity wall. In rear of the property (I live in a 70s build bungalow) there are two brick air vents which appear to have been filled with expanding foam by the previous tenant! Do I unblock these or not?? Insulation in the loft apparently is sufficient but around the eaves is going to be further inspected by roofers by removing a couple tiles. The condensation and mould appears in bedroom, bathroom and kitchen, and yes I have the trickle vents open 24/7 and open windows daily, even for an hour or so during winter months.
i use a £15 infrared gun thermometer to dind the cold areas in walls and ceilings - they were in the top 6 inches of the walls, i kingspanned them during roof repairs
Hi Rodger, thanks for another informative video, we live in a bungalow with these air bricks west facing front and back east. When we moved in most were covered up, I removed all and we get lots of mould on the west side, should I cover all and the loft gaps? George Staszak Mr Combi 🤩
Regulations for brick or block clad timber framed buildings require cavity ventilation top and bottom. That said, I do wonder if what they require is sufficient to make much difference.
There is a huge difference between a rendered block wall and a brick wall. Especially with hard bricks, driven rain can actually spurt into the cavity.
With wide insulated cavities I believe there have been practically no issues, and any probably poorly fitted cavity trays.
Retired Architect.
ps, when I started, before sealing the top of a cavity, the builder would go round with a long 2x1” and knock off any snots on wall ties.
@@markthomasson5077 In Australia our bricklayers hose the cavities out every afternoon, they also leave clean outs at the dpc and those that out every day. I don’t see the English brickies do that.
Pretty sure my double air bricks (double the height of a brick) vent both the sub floor and the wall cavity - I live in a 1960's bungalow. I've always wondered if the air from the air bricks is cooling the cavity and therefor providing heat loss.
You don't dry your clothes after washing by putting them in a closed plastic bag, you let air movement (draft or wind) on them to dry them out. So how does sealing the cavity help get rid of any moisture build up, be it from penetrating water from rain on the ouside courses of brick, or inside from a leak of some kind. Once you get moisture laden air you have condensation somewhere. Lack of air movement in houses is one reason we are seeing so many pictures and click bait stories of black mold. I love seeing these pictures of huge horrible mold in houses - basically means they are too lazy to clean it off !
This is also my logic, better blowing into the loft than soaking into the internal skin? Or mold filling the cavity. Perhaps this is in reference to new builds. Either way, often these short 3m videos leave more questions than answers. Rogers longer form content is much better.
If you have alot of moisture in you cavity there are propably things you can do first to avoid that. But ofcourse you can live in a area or in a house were cavity insulation is just not an option.
Black mould is a PITA. We have all upstairs windows left on vent 24/7. The bathroom and kitchen have extractors venting to outside and I clean the grilles and duct once a year (doesn't need anymore than that it as even then they aren't particularly dirty). I open all windows in the house for 10-15 mins twice a day. There is a 'healthy' draught unser the front door too.
The children have a moisture absorber (unibond ring shaped model) in their bedrooms too. Probably only removing trace amounts of moisture each and only a portion of any excess when their blinds are closed which will almost seal off the vented window area.
We still get black mould growing in the bathroom on the walls and ceiling and a bit in other rooms around the window reveals. We hit it with a dedicated black mould remover every so often (tried both HG and the Bang brands). It always comes back.
Victorian house with no obvious damp issues - we had areas that were picked up when we bought the house treated and that seems to have been good for the ast 19 years - skirtings, plaster, paint no problem at all.
Central heating to every room although generally set at 18 unless we're feeling the chill and then we go up to 19.5.
Not sure what is going on but it's annoying. Not huge patches of the stuff and we're all relatively young, fit and healthy so not at major risk from it. Be nice to get rid once and for all though.
great stuff your the best
I have polystyrene in my 25 yr old house. Put in the cavity by the builders when being built. Was this ok.🤔
if fire spreads to the cavity its too late ! hopefully the alarms have already gone off and youve escaped
I've got an odd internal cavity vent (white plastic louvered thing) on the internal wall of a cavity wall situation. The gable end is north-facing and gets cold bridging along the bottom sometimes causing condensation (the condensation pattern seems like it follows the mortar detritus etc in the cavity) , and I wondered of this was a 'fake' solution to that, or if it was where they put in some fibreglass insulation (which is in there) and never closed it back up properly. It's very strange.
Do you have an open fire in that room. If so it may be there to allow air in to feed the fire
@@chapman9230 Thanks for the reply. 👍There's no open fire in the whole place. I can only assume it was either to placate the previous resident/s about the condensation or to install some fibreglass cavity insulation, it just seems very odd.
It doesn't go through to the outside wall and isn't sleeved, when you pull it off to reveal the hole (5/6 inches across) you can see the insulation so maybe it was to do with installing that, but I haven't yet come to a satisfactory conclusion about it.
For example someone suggested it might have been for a tumble dryer exhaust, but as it doesn't go outside and is in a position where you would never put an exhaust/dryer I have ruled that one out.
@@thesunreportI suspect it used to go to outside and be sleeved as a vent for the room. But then when cavity wall insulation was retro fitted they bricked up the outside vent and just left the inside with the vent face.
I have removed the timber floor and made concrete floor can I get rid of the air brick ?
If it's slab on solid then yes, air bricks below DPC are now doing nothing
Each of my bedrooms in my 1950s house has an air brick at high level. Are these for airflow to combat damp? Would I be okay bricking these vents up?
I've started seeing quite a few Cavity Wall Insulation Removal Vans in my area recently.
Why might that be Rog? Not being facetious.
After a recent outbreak of dry rot in a suspended timber floor I wouldn't dream of bunging up the cavity wall in my old 1930's semi.
Horses for Courses? I'm also up North, tis Grim.
hi Grim!
Cavities are ventilated by perpend vents. Air bricks are usually for ventilation of voids. Dry rot is different from wet rot.
if theres a prevailing wet wind onto the wall the cavity insulation may get wet
If the cavity is trapped, would that not cause condensation inside and psosibly cause damp and mould?
Yes. 100%
No, Roger said that any water/condensation should be allowed to soak away into the ground.
It would condensate, but then drain away, not much different than venting the cavity.
@@chrisallen5548but it wont completely will it. In the long winter months with any driven rain and even condensation, that cavity would remain damp and begin to mould up on any smooth surfaces in particular. I would personally leave the top of the cavity open and insulate with something that doesn’t hold moisture. That is unless you can, with absolute certainty, prevent any ingress, apply lateral vapour control and seal the cavity entirely with no airflow. Borderline impossible.
Now most roofs are ventilated at the eaves and in the loft space so no need to close off cavity like that.
I had a call, after cavity wall insulation fitted, mould and damp build up.
Now the FB damp & condensation group would be jumping all over this as they see cavity insulation as the devils own work.
I actually posted my thoughts & solution as below & got banned!
What it was, was the air-vents fitted in most rooms, had not been sealed where they go through the cavity. House built before we had plastic vent liners. So the vent hole also got filled with insulation thus blocked the vent.
Simple solution, tap out the old plaster vent and fill around the cavity with squirty foam, to hold the insulation back. Fit a new plastic vent.
Does the moisture evaporate/drain back out through the cracks between mortar and brick?
Evaporates and drains into the floor, if enough had pooled and there was an escape out the mortar or brick the water would find it.
I would argue that each building design is different so a 1 size fit's all approach doesn't work. Some houses need the airflow/cavity regardless. Filling it will just cause issues. The building next door might be similar but is ok with cavity filled with insulation.
Materials used, quality of the job will all effect the outcome.
and local weather - in a wet wind or not ?
Does that apply to timber frames
No. Timber frame cavities must be ventilated at high and low level at each storey with perpend vents. I’m surprised and disappointed that this wasn’t mentioned as timbers frame is the predominant house construction type nowadays.
Ideal conditions for growing mushrooms.
Brick quality is important for cavity walls.
Ah so I could trying to block the cavity left open in the loft ? I have them open and get the odd rat every now and again coming it. God knows from where but keeping it in the wall in better than the loft.
God I love this channel
We've got a single storey extension with cavity wall insulation whereas the rest of the house hasn't, the extension in theory should be the warmest part of the house BUT the extension has vented sofit, the cavity isn't closed at the top and the interior walls are dot dabbed so air leakage negates the insulation, if I ever can afford to have my own house built I've got all the spec planned out 😂
Almost 30 years ago, I worked doing blown cavity wall insulation. It was the fad back then. Hindsight is always great! lol
Still use it on new houses. At least they were five years ago.
Roger, silicone around wooden windows just rots them out. Silicone around plastic, mortar around wood. No ifs, no buts dear boy!
I’ve got rats going up my cavity wall into the loft so I know it’s not capped!
Nothing new? I have original ventilation blocks in my 200 year old "solid " stone walls. Not through but on outside of walls only . Walls are usual 600 mm thick of two skins with rubble fill. It is often said that if you can ventilate somewhere then do it, even if only trickle
It's terrifying thst we still apparently don't know how to build houses in UK that aren't freezing &damp
Im self building a house with partial fill cavity wall but no one seems to close off the top of the cavity in our area.
Since face brick outer skin lets through a lot of wind driven rain, if i close off the top how will this escape, both the water pooling at the bottom of the cavity, and the condensation from it trying to evaporate?
The bottom of the empty cavity is 300mm below outside ground level, which is clay soil so weep holes wouldnt work, they'd be blocked or letting it in.
I'm going to apply stormdry masonry cream to minimise the water ingress.
Yes the best way is to use a masonry cream. We do this with chimneys. Prevent ingress....allow breathing
Well done, very well explained, I've been trying to tell people the exact same thing but there all super intelligent builders and don't want to learn any more.
No I lived in a coal board house from the 1962 up to 2014 and I never had any cavity wall insulation fitted and we had no damp and there was air bricks fitted to every room in the house and they did there job even at winter kept open ok
Like everything need installing correctly, CLEAN CAVITIES CAUSE NO. PROBLEMSCAVITY VENTILATION AND CAVITY INSULATION CONFLICT@
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Je suis cavité
Do we block up all the weep holes as well then?
If ever there was a waste of time it was weep holes. The Germans don't use them so why do we?
When cavities were ventilated we didn't have half the problems we do now.
We have to fit cavity trays halve way up the building, why? All that plastic just adds to condensation.
As for closing the cavity at plate height, (loft) haven't done that for years.
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So many times people say... "Yeah but It's meant to breathe" ... 😂😂😂 Seal-off your cavity, seal everywhere with damp membranes, seal the windows and doors well, DO NOT ALLOW ANYTHING TO "Breathe" 😂 use dehumidifier in your homes people. Toilets and kitchen need good extractor fans, and thats it. Dont let your walls and exterior fittings breathe 😂
Do all that and you're going to have abysmal air quality in your house.
@FureyinHD maybe open the windows ...?
We seal tops now with firesocks and cavity closures.
Hi Roger, up here in Scotland for the last 40 - 50 years the majority of new build houses have been timber kit construction where it is essential that the cavity is ventilated. The regulations state that ''Cavities should be vented to the outside air by installing ventilators with at least 300mm2 free opening area at 1.2m maximum centres." This is normally achieved by installing ventilation cassettes similar to weep vents but full hight of the brick (65mm). The cavity fire barriers should also be taken into account with the placement of ventilation cassettes each side of the barrier. This ensures that each fire compartment within the cavity is properly ventilated with ventilation cassettes at the bottom and top of each compartment.
Why don't you do a collaboration video with someone who is fully up to speed with the Scottish regulations and practices. I'm sure your many Scottish subscribers will appreciate it.
Good videos. Your plumbing ones in particular are excellent.
I should have added that we do use cavity insulation but it is now generally a solid sheet installation that doesn't completely close the cavity. An air gap is always maintained to provide the ventilation.
I'll second the Scottish request!