Garden Room Workshop Extra | How I'd Construct a Cold Roof
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- Опубликовано: 27 фев 2021
- Hey everyone 👋 In this one I take a stab at how I'd go about constructing a cold roof for a garden room, demonstrated with some SketchUp plans.
Gapotape: gaposhop.com/
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Thanks again Ali for all your excellent videos. Keep them coming.
Priceless information as always!! Have your videos on repeat and made loads of notes, sketches, etc. in preparation for summer build. Never thought of 50mm insulation for warm roof... back to my spreadsheet to see how much space I have! Cheers and looking forward to the next episode!
This is absolutely great timing as I’m just about to build mine. I’ve enjoyed all your videos, so well explained and easy to watch many thanks for sharing all your videos 👍
The petrochemical industry has really done a great job. Everyone insulates, seals, coats and bonds with plastics. Soon the wooden structure will be replaced by chipboard, OSB or MDF boards bonded with acrylic glue. There are so many natural alternatives, such as hempcrete, straw, clay, hydraulic lime, hemp seals, which do NOT release plasticizers and do not produce hazardous waste. A friend of mine put it in a nutshell: The product that is “perfect” in the seller’s mind is one that immediately becomes garbage when it goes over the counter. Compare the lifespan of plastics compared to clay and lime plasters, untreated wood, natural fibers and much more. And I'm not talking about the health benefits or sustainability. All you need is know-how and a few good friends to help you.
Hey Ali, Great videos. Super useful. Looking forward to part 20. Many thanks
I'm with you on the insulation... followed your video series and built my stuido with a warm roof and 100mm PIR insulation, floor, walls and roof. Even on the coldest of days it's toasty warm. With the A/C in summer it's a delight too. Thanks for the series :)
Great explanation as always. Cheers Ali
Thank you I did not had clear idea on the importance of air tightness and air movement. This makes it clearer.
Hi Ali. Great video again. I’ve just finished my cold roof and pretty much exactly how you explained it, although I went with cutting a 100mm square box in the PIR to house the downlights. I’m still left with 50mm out of the 100mm PIR above the light so still quite heat efficient. You’re right though that you also need to cut a hole in the VCL. However some polythene jointing tape around the inside of the box can help with that. What surprised me is how strong the airflow from front to back in the voids is. My garden is not that windy but I guess some kind of pressure differential dynamics are at play which create that air movement. Definite proof that the ventilation will do its job! You’re right that cutting and fitting PIR above your head is a nightmare - goggles and face mask a must - I didn’t use gapotape instead just put some temp nails in on the bottom edges of the rafters to hold in place until I went to town with the expanding foam.
Thank you for another great video! I went with a cold roof and had the same thought but I used a Thermahood fitting to keep the insulation at 90mm and ensure I had a good seal. It also means you can use conventional downlights.
Excellent video, thanks
Fantastic video
Brilliantly clear explanation Ali. Cheers! 👍🏼
Still watching then Rhys? 😁
@@AliDymock subscribed since early on! Just starting to clear garden although house extension may delay the garden room build.
Thanks very much, this is really helpful.
Another high quality and very informative vid - thanks for sharing 👍
Thanks Paul!
@@AliDymock Slightly disappointed not to hear any DJ Quads tracks but I won’t deduct any marks for that 😉😀
excellent well explained video,thank you
Excellent video, thanks Ali. I had completely missed that the roof noggins have to be shorter than the joists for the airflow.
Great shout Ali. I think I didn't consider airtightness enough on my design and now wonder if it could've been warmer.
One thing I found making my fairly small garden office mostly air tight was that you do need to crack a window or use trickle vents if you are in there all day to stop co2 levels rising to much
Very interesting and reassuring as I basically did this already. I literally put my roof insulation in today using nails to hold the PIR up where it isn't supported by the head plate. I have already used firring strips and notched sections out of them for the cables in my cold roof and for across joist ventilation as well. I have vented soffits on all four sides to compensate for the fact I dipped just under the 50mm gap on the back side where the firring ends. Another lighting option is LED panels which is what I have gone for as I dislike downlighters. They only requires 1 cable poked through the insulation but they do eat about 5cm into the head height. My cladding is being delivered in 2 weeks so fingers crossed for your cladding video soon! Cheers
Well done Steven, sounds great. I'll do my best. Next video is the hump but I've outlined it already. The rest (cladding) should be plain sailing.
You'd be surprised how many 'builders' I've asked to quote me on a warm roof and they've just look at me confused, as in what's that? We currently have a cold roof on our extension as it's cold has pie, especially in the winter months. Tbh, warm roof makes total sense and after watching your garden room series... i'll never to back to a cold roof again. Looking forward to your new garden room project, hopefully it there won't be such a long wait this time ;)
Thing is, they've almost certainly built one but don't know what it is or why to do it a certain way. At the garden room house I see the next door neighbour's extension built just 3 years ago slowly getting roof troubles, bubbling paint etc. Yeh, there won't be so much explaining, mostly doing so aim is to get it out quickly...once I start.
Great video as always Ali. A couple of quick questions, Would there be a need for airflow between the plasterboards and the underside of the insulation sheets? Also, out of curiosity, I'm very impressed with your technical knowledge - what do you do for a living? Many thanks and keep up the great work!
Impressive effort, Ali as I'm sure you are probably sleep deprived right now! I was expecting a long gap for any new content so I was wrong. good use of Sketchup.
Ha, totally sleep deprived but I'm doing my best to release more regularly regardless. This video just kind of fell out of Part 20 which is mostly written now 💪
Interesting video.
I have built a cold roof on my workshop in the garden.
I used joist hangers to put the height of the roof joists within the height of the walls. I wasn't bothered about a significant overhang. Then covered the entire building in Multifoil. 40 layer on the roof and 21 layer on the walls. Everything taped so it's now insulated and vapour barrier all in one.
2x2 timber followed by 18mm ply then EPDM on the roof to form a gap that air flows from the low side to the high side.
The walls are cross battened with 25x50 lath to allow air movement up and across. Finished with 25mm board n batten Siberian Larch vertical Cladding. All window sills and door frames are hardwood.
And to make things more complicated than they had to be, part of the wall opens up to create a 6ft gap to get equipment in.
Nice! Sounds smart, especially the wall that opens up!
I think with this video Ali you’ve almost convinced me to go with a 50mm warm roof if I can keep it under the 3m as my wall modules and base are quite high. I’m not fussed on getting the ceiling boarded so a warm roof would make it so much easier for the electrician to do the lighting etc.
Cool! I'm thinking the exact same, keep the ceiling open in case I want to store stuff between the joists and it will feel taller (workshop-at last). 50mm + a tight VB will be very warm. 👍
@Ali Dymock. Great content as usual. About to order the materials for my build and going for warm roof (planning has been submitted and is going through process now, both neighbours have been told and they’ve received letters from the council and no objection from them) with 100mm PIR but now thinking about 50mm on top and then some rock wood in the building. Rock wool more for sound insulation as my house backs onto the local park with lots of kids shouting and making noise., what are your thoughts? Keep up the good work and looking forward to the next instalment
I wondered if you might do it all again since you moved! Great news 😁👍
It would be rude not to! Gonna focus on speed on (low) cost 👍
Ali!
I used 50mm PIR on the warm roof of my build. It's a woodworking workshop and through this Winter it's been very warm and dry. One wall heater which really only goes on to take the edge off - always warms up quickly. Very little condensation and no spiders... 100 mm Rockwool in the walls and 50 mm PIR between the floor joists.
Again, many thanks for giving me the get-up-and-go to actually do it. Hope all well with you!
Best aye.
That's awesome to hear and much as I suspected. B regs U-values are quite misleading. Planning the same, 50mm PIR in floor and walls and rockwool in the walls I don't think you sent me a finished photo?!
@@AliDymock Er, no. Not yet...
Perhaps because it's not quite finished yet... I changed my mind about the fascias... I'd got a job lot of Larch for cladding from a local sawmill and several of the bits were wide/long enough for fascias so I put them up. Not really satisfactory though so I recently ordered some plastic fascias. Just easier, much lighter (!) and less prone to movement. Aside from trimming out the windows, the inside is finished. Decided to build a wee shed for dust extraction stuff and hang it on the end - pretty successful and I'm pleased to regain the internal space all that took up.
If you like, I'll email you direct with build pics and the status quo...?
Are you happy with how you've built it in terms of sound proofing? I am so considering building a workshop in my garden for my joinery business but worried about neighbours complaining about the noise.
@@ChickenDinnerz Hi,
Yes, I'm pretty happy. The insulation is 50mm PIR on floor and roof and 100mm Rockwool in the walls. I lined the walls with 18mm MDF. Went with the MDF instead of plywwod/OSB because of the density - as to whether it's better from a soundproofing point of view, I couldn't really say - nothing to compare it with.
What I can say is that the loudest tool I have is a 12" P/T and the noise is - according to my neighbours - acceptable...
Heat/insulation-wise I'm happy with what I used. I suspect it would be adequate in a house too.
I built it the same way as Ali built his except that I used Larch as external cladding. This is batten and board with the b and b fixed to 1" battens and the boards themselves being 1" too. Not sure what, if any, difference this would make to the soundproofing/insulation question...
Hope this is of some use to you...!
Best aye.
@@alasdairmackenzie515 thanks very much for that, very helpful. Would be a nightmare to build it all only to find it's still too noisy for the neighbours
Cheers Ali, as you know I've been awaiting this video and whilst it's helped massively its also made me once again ponder the question.... Warm roof or cold roof? 🤔
I've a little time to ponder whilst I draw up my plans but honestly, these videos have been a massive help. Will be in touch soon in regards to the edpm. Thanks again.
Warm roof always better than cold roof Mike. It’s the 2.5m height restriction that forces many down the cold roof route , me included. If you can get planning permission for 3m or so it’s a no brainer.
Would 50mm insulation on a warm roof be enough to stop any condensation from forming? I've been searching like a maniac for hours now but can't find any information on this. If so this would solve all my problems. I can actually manage to get away with 60mm.
It's a great question. I don't know for sure but I very much suspect 50mm is sufficient because with a hybrid roof with insulation above and below the sub-deck the insulation below cannot be too thick otherwise it will bring the dew point below the sub deck. Generally no more than 25mm is advised which makes the whole hybrid roof a bit pointless (lots of cutting for just an extra 25mm) So with 50mm above the sub deck it should be fine.
Good video - thanks ! Doing my garden room with 50mm PIR insulation in a cold roof, 40mm in the floor, and 75mm in the walls. It will be interesting to see how it performs ! Just managed to beat the c15% PIR price increase that is imminent ... and went for slightly thinner than planned boards to take advantage of what was in stock at the old prices.
Nice. I reckon that will be very cosy. What's going on with PIR prices? I haven't kept up
nice.
Ali great videos, was thinking SIPS, what do you think?
Hi to install downlights do you have to make a hole through the insulation ? Or could you put downlights below the insulation without cutting it ?
Ever thought of Rafterloc PIR sheets for the roof? Easier to fit.
Your videos have really helped me, but my design is obviously a little different to yours. I am building a cold roof and am concerned about my choice of sheeting material. My garden room is 5m x 3m. I went for 18mm plywood. The problem that I am concerned about is that the noggins are 4x2 to allow a ventilation gap (joists are 6x2) and there is nothing to support the plywood sheet joints between the roof joists. I am thinking now that tongue and groove OSB would have been a better option but it would be expensive to change now. A couple of questions if I may.
1) would you lay the sheets longitudinally in line with the joists to reduce the total length of unsupported edges, or would this reduce the strength of the roof too much?
2) would you screw battens from underneath to join the edges? I am concerned this would reduce the airflow too much e.g. from 50mm to 38mm. Would metal screws be a point for condensation in the cavity?
3) would you lay a second complete layer of sheeting (maybe 12mm ply) over the roof to bridge the gaps and secure the joins?
4) would you paint the underside of the plywood with wood preserver to help prevent mould or rot or insect invasion etc.?
Did you have any problems with timbers that aren’t quite straight? Even a centimetre out over 4m means that the plywood has to be forced to bend quite a lot to attach to adjacent joists.
Great content Ali, ....shows you have picked up a wealth of information since the outset !!
I learn from you guys 💙
Really intrigued to see the "box-type", there is very very little online about how to achieve!
It will be right at the end of the video :)
Question, if I put two separate sheds next to each other would I still have to adhere to the 3m x 5m maximum size? Or is this only for a single outbuilding?
Great video, and well explained info. What planning software do you use?..... or any recommendations
Cheers and keep up the fantastic work
Thanks Leroy, this is all done on SketchUp. I did a crude sketchup diagram for my build but had forgotten it all so I've been re-learning. It's a bit clunky but with some perseverance it does the job.
Superb content. Starting my garden office this week. Gonna taper the overhang rafter ands to reduce the visual depth of a warm roof. Any thoughts?
Yeh, I think it looks dope. Like Nick's www.alidymock.com/nick-somerville/
I might have missed the video but is there a video of fitting sky lights to a cold roof and ventting around light but no unsightly mushrooms in the rafter spaces
Just one question: Doesn't the foil on both sides of the insulation create 2 vapour barriers? As far as I've understood that's not a good idea, but I am probably missing something.
Hi, Love your videos, never watched others that actually put confidence in me. Can I ask a question? I am insulating (cold roof) my workshop but only have 65mm/2.5inch joists. I can either get 30mm or 40mm PIR leaving either a 25mm or 35mm gap for the ventilation. I have soffit vents all the way across and a open channel the other end for ait flow.. Would you go for the 30 or 40mm PIR? is 25mm air gap enough? thanks! (my workshop is 10 x 16ft).
Hey David, so glad you like them. It sounds like you have lots of vents and the span is reasonably short so I'd probably err on the side of more insulation and leaving a really went ventilated 25mm gap. Either way there's some kind of compromise but in this case I think it's a reasonable one to reduce the gap. It's the same depth of gap as behind my cladding and that's fine so I say go for it. :)
Hi mate, what you think About hybrid roof ?
One thought, why not used the Celotex at whatever you can afford/want and fill the void above with Rockwool?
Hi Ali, another great video. Tell me, what is the name of the tape you are suggesting for the pir panels. It sounds like you are saying “gapper tape” but I can’t find anything like it.
Heheh, GAPOTAPE. There may be similar stuff out there
Thanks, a much better explanation than you get from a certain commercial builder of these rooms!
Hello from Seattle, WA! How would I create the vent if I don't have an overhung soffit, in other words, the massing is a simple box? You mentioned that at the end of the vid. Any insight would be appreciated!
I have a similar issue with my building
50mm warm roof. 100%! I even think you could go lower and still reap the benefits of air tightness.
I’m going for exposed copper conduit for cabling. I think it looks great and don’t have to touch the vapour barrier.
Yeh I reckon you're right. Copper conduit will look great 👍
Interesting to see you’d go 50mm in the roof next time. Would the same ring true for the floor also then? Thanks for all the content. Really helpful stuff 👍🏻
Yeh, what I did was overkill I think. If you stop drafts then 90mm+ insulation isn't needed. So I'm thinking 50mm in the floor and roof, that way I can just buy once and use scraps from the floor in the roof (the plan is for a concrete base). Then rockwool in the walls. I want it to be quick and cheap!
@@AliDymock I’ve fallen down a bit of a rabbit hole with this and with the cost of PIR and OSB I’m moving into the value engineering stage of my design! Good to hear your experience and reflections on this. Cost wise I’m team rockwall. Wickes has cavity slab on offer that I think I’ll just have to make it work for the £/m2. Are you documenting this new build?
I would counter batten between joist and plasterboard, that way u have a void for cables and no need to compromise the vapour barrier, i have an art deco house thats entirely flat roofed (cold) and this is what i did. I used 25mm roofing battens. I did have tall ceilings to start with tho. I insulated between and below joists with pir.
Insulating below joists must make it very warm. Wouldn't the screws attaching the battens puncture the VB too though?
Not as warm as I would like, its 125mm in total but i have solid walls and 90s aluminium windows so need to work on those at some point, or may even externally insulate when I re render.
screwing in batterns does puncture it but the batten compresses against it so its not that critical i don’t think, u could run a bead of silicone along the batten. Also the amount of screws needed for the battens are far less than the amount u you would use to plasterboard straight to joists. So less punctures. When you do board just need to make sure u get screws that dont go further than the batten.
Also, using foil backed plasterboard is another vapour barrier but also it apparently bounces the heat back and forth between the plasterboard foil and the foiled insulation. I didnt use foil pb in ceiling but as an experiment i did use it on an external wall (wall>foil pir insulation>batten>foil plasterboard) and i am not convinced that.
Gapotape looks like great stuff but it pretty much doubles the cost of insulating so it's a non started for me. If you did use it to wedge PIR above down lights I'd still whack 4 60mm screws in front of it that stick out of the rafters by 30mm to make sure the board cant drop.
What software do you use to design these?
Please let me know what you suggest i done my garage roof with plywood and rubber what shall i put underneath? Cheers
Insulation! But just make sure it's vented at each end.
What would you do if only one side was able to be vented? Say the other side butts up to a wall or something. Thanks for all the stellar tips.
Hmm, it's not ideal, you really want that through-flow of air to remove the moisture otherwise it will become stagnant and moisture can build up. How about a vent in the top of the roof like I show in the video with holes between the joists to allow all of the joist voids to ventilate?
@@AliDymock I already drilled some small holes to "connect" all the voids between the joists. Probably will add a vent as well like you're suggesting. Thanks!
Is your website offline now ?
How do you insulate a shed floor?
Hi, hope all is well? Not sure if you’ve already answered but what’s the difference between a cold roof and a fully insulated SIP roof(warm roof).
Have you seen the hybrid roof that Oakwood Garden Rooms use? They push the pir up against the roof osb then have an air gap (ambient temperature) then moisture barrier and then plasterboard. Worth looking at maybe?
Ali, did you consider cork for insulation?
I am thinking about it for my garden room, but I could not find anything about garden rooms insulated with cork.
Well I'm aware of it but I didn't really consider it. Being lightweight with holes in it I imagine it does a decent job of insulating and perhaps it's cheaper these days since more and more wine bottles are getting plastic corks. There are a few eco insulating materials like sheep's wool or hempcrete etc you could look at if that is your reasoning
@@AliDymock roger that, thanks a lot
Hi Ali.
Slightly off the topic of this video but I'm looking at building a shed/workshop it will be under 1m from the boundarys, i see you have done the same with your build. Are you using non combustible cladding or are you going down the road of vanishing the timber cladding with a class o fire varnish??
Hi Matt, the more time passes the more complex this issue has become because every council and probably every private building control will have a different view on what's 'non-combustible' or if they even care for an outbuilding. Some will insist on a brick/block building all round including the roof. Other will sign off cement boards, others a fire retardant spray. It's a minefield. If you want to be above board find a building control that will sign off what you want to use.
@@AliDymock thanks for getting back to me Ali. I'll give them a call and see what they say. How's the workshop coming on anyway??
Hi Ali! Great vids as always. I’d be interested to hear if you have heard of and what you think about approaches of a “hybrid roof”? I’ve seen this in another video where the suggestion is that if you push the PIR right to the top and leave the gap below, then the air in the void will be at ambient temp and therefore won’t condensate? It seems to make logical sense and, as with all things, it’s a compromise...but I wonder what the true likelihood of any issues further down the line would be....
What did you use to do the drawings trying to save on getting a architect and do it myself for planning Permission
Google Sketchup
How much has the whole build costed?
Ali have you still got the discount on the edpm rubber ? If so how much is it please happy to email
Yeh just pop me an email and I'll send it across
There is a formula for cutting holes in roof joists, you certainly don’t cut holes near the end of the joists
why not 400 centres ? great vid thanks
Well in this case it's just for demonstration, quicker to make in SketchUp and looks a bit cleaner on video but you can go with 600mm centres, even if your walls and roof are on 400mm. If you;re using rockwool the 600mm batts will fit very nicely