How to remove a roof purlin for a loft conversion
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- Опубликовано: 5 янв 2023
- How do you remove a roof purlin to allow for a velux window? In this video a structural engineer explains what a purlin does, and how to remove it as part of a loft conversion.
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This video is for entertainment purposes and should not be construed as structural advice. Any structural alteration should always be designed by a competent structural engineer and signed off by a building control officer. Failure to do so may reduce the value of your property substantially and may impede the sale of your property in the future. 
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We always put a top plate in above the studs, I believe the rafters can still deflect when using the single stud approach, double bolt the collar tie
@Robin de Jongh. That was beautifully explained. A level physics, Architecture at University and loft conversion. I new what to do and how to do it but never had it explained so simply.
Evening, as a carpenter all good advice far more than I could ever imagine being a able to come up with via computer.! all I would add is the continuous head plate of the ashlar wall should be birdsmouthed into the rafters which wasn’t mentioned and most reputable inspectors would insist on at a depth of no more than 1/3 of timber this method is by far the best way to go for a number of reasons. Also the existing spans should be ignored in 99.9% of roofs as when built they where nowhere near up to todays regs. So best just look up spans dependant on pitch,timber sections being used loadings etc all the best…
Thanks, that's great advice. Please comment on other videos too, as I'm very interested in a carpenter's point of view 👍
Like birdsmouth the new uprights into the new head plate that is joining all rafters? Sorry kinda new to all of this roofing and I'm really trying to get a handle on it all 😅
Our guy didn’t birdmouth the joints. Building inspector went mad. Told us to use clips. Ok great, all sorted until it was time to put the kingspan in. Absolutely bloody nightmare!
@@baseddept. apologies I’ve only just seen your comment, no the continuous head plate of the ashlar wall is the only timber member that should be birdsmouthed into the underside of rafters. The uprights are then just fitted as square cuts between the sole plate and head plate like you would a traditional studwork wall I try to align the studs with the rafters also to give a solid transfer of loading. 👍🏻
Got to say this is very good sir . I’m a carpenter of 20 years not done loads of lofts but do know what I’m doing and go belt and braces with what I do . Seeing it on a computer is really nice touch. I think lots of customers would like to see me do this but I can’t Work a computer lol
A brilliant explanation with excellent "Graphics" and simple presentation. Thanks
Perfect for the indoor gardeners.
lol. Plenty of insulation as well then
Excellent video with no silly music or men in back to front baseball caps
You the man Robin!!! You explain it so simply!
Thats exactly what I did, as advised by my building inspector 👍🏼👍🏼
This is exactly the process I'm doing! Great explanation.
Very useful information Robin. Thanks.
great explanation clear and simple
When I did mine I put the purlin wall under the purlin position so it still retained it's original strength as per the span of the timber. The room was smaller as a result but I use the eaves as storage.
That's cleared up some questions I've always had👍
Nice vid - quick, clean and to the point. Lovely. Thanks.
You're welcome!
Thanks for this helpful video. Sorry if I missed it, but what about using noggins or braces between the rafters in the longer spans? Is that OK? or not recommendeded?
I've an end-of-terrace hip roof, so this goes very close to what I'm trying to figure out.
Thanks for the video, Looks like there’s quite a few people looking into this scenario, we’ve got 2 purlins on each side set at 1.7 apart. Problem we have is the purlin bracing is done by the internal brick walls transversing the house and these continue through into loft right upto the rafters, surrounding the purlins.
yours is a very standard arrangement as with hip roofs there are no gable ends to bear the purlin ends
@@stevehallam6495 thankf for reply Steve, ours is 1950 detached bungalow with gable end both sides, about 9x9 footprint with 3m joist to ridge. Believe it was the Forman builders so he over engineered it. The roof it’s self is as straight as a die!
Hi. Great set of videos. I have a roof with the same setup but half way down the loft I have 1 set of 8 x 1 creating a inverted triangle to the centre of the property on to a central wall .Do you have a video to remove this. Thanks again Jeremy
Our loft is same as yours. A surveyor said the purlins need support from below to a loading wall, we had loft boarded /plastered 20 years ago, not sure if supports were there. A builder said they can do vertical down supports from the purlins similar to what you show, or the can go across to join the load wall which would ruin the room. In your opinion , do the purlins need support ? 😁 great video , and thank you
Fantastic video. Thanks
Hi robin, instead of putting in ties between the rafters could you also use a joist running from wall to wall at that 2.2meter height above the top of the stud wall.
Makes a lot of sense. Do you by any chance have a presentation for a Hip to Gable conversion ? Semi bungalow with gable built with stud work and cladding, not brick ?
So useful to be told WHY we need the low wall, plus the cross bars at the top. Now I know to use the measurements to replicate the original loading, I feel much happier about how to compensate for losing a purlin. My only issue now, is that I have a four way hip roof with a ring purlin, and you didn't explain if a part of a purlin can be removed, or whether the ring purlin supports/strengthens itself by dint of being a continuous ring? If you (or anyone else who knows) could let me know, that would be wonderful?
Good video, can you run a video for a ridge beam? people say the ridge beam does not carry a significant load? is it always the case? Can you provide some examples and talk about the ridge beam, in some loft conversions the ridge timber beam replace with a steel beam, in this case, is the load path changing?
Do you need the ceiling joists or could you take this away now and have a exposed ceiling?
Great explanation, thanks. What software are you using?
Always useful. What about king post truss lofts - there are two in my loft….?
Robin, you can also strengthen the rafters by bolting larger timbers, say 7x3 to them.
Yes I agree, but you will still need the main beam.
This is amazing and found this video bit late.
What you think if we remove a purlin with vertical Support and replace with just a steel without any vertical support?
Hi Chathura.That sounds like it could be a good option. You will need to have the steel design by a structural engineer.
Great video, another useful way of removing purlins ( as long as you are happy to lose access to your eves or fit additional loft hatch) is to create a box beam in place of the steel using a timber joist, studwork and 18mm staggered ply.
Hi Steve. Absolutely, see my video on this here ruclips.net/video/hgH9z_JJDXk/видео.html
@@RobindeJongh Do you submit calculations to building control ?
This looks pretty much identical to my scenario. Can you give any info on working out the flitch beam specs in this example, Robin?
Mine is a 6.5m span and I'm trying to figure out whether a flitch beam would be sufficient.
Thanks again. 👍
Just saw this video thank you! Quick I ask a request for a video. I live in a detached house with two gable ends. The purlin timbers are supported in approximately 2/3rds across in the loft by a supporting wall. Is it possible to remove this wall at some point to open up the whole loft?
Hi Reuben. I plan to do a video on that soon 👍
Propper dinlow nailed on a seat cut or atop plate and then a collar for storage lofts are all ready used for storage so no need to flitch beam the floor regs have changed a lot that's a 1990s loft job
If I'm not mistaken, your design there shows boarding going straight on top of the original rafters. Could continuous Walking on that cause the plaster in the house the crack?
Hi Iain. There is a new floor spanning between the flitch beams. Please see the previous video for details: ruclips.net/video/xDddwHq68QE/видео.html
Very interesting! We had a loft conversion 23 years ago, and the first thing the builder did was cut the purlins up with a chainsaw, causing the rafters to sag. He said that the roof wouldn't collapse over the course of a few days, and the new structure would restore its integrity. Who was I to argue? Even though I don't think he took any measurements or did any calculations. Anyway, the new members looked similar to those shown in this video, and the roof is still in good condition, so I suppose he was right. It was all signed off by the council building inspector too.
The problem for the builder is that the purlin impedes new rafters going in. Hence with the design I've shown, the rafters get supported first before the purlin comes out. See my next video 👍
@@RobindeJongh Thank you. I don't think my builder saw it as a problem! Thinking about it, he did plant new, deeper rafters alongside the original ones before fitting insulation, but I don't remember if the new vertical supports had already been fitted by then.
Many thanks for this. The purlin(s) in my loft also has a couple of diagonals focused towards the centre of the loft. If I follow the above advice, can I remove purlin(s) and those diagonal pieces of timber?
The diagonal bracings are to support the roof purlin due to the long length of your purlin I imagine.
Your purlin must be undersized to span without the middle diagonal support. It would have been done that way because large section timbers are expensive compared to a smaller timber and an additional short prop.
@@stevehallam6495 Mine built is '64 has a scarf joint halfway along, plus angled supports going into the middle.
I had a the same problem with multiple struts ith quite low collar beams, some with a plywood bracing spanning between them too,along the thoroughfare of the main attic,the purlins were quite significant but because they spanned quite a distance they required the diagonal struts .Fortunately I had the advantage of my free architect also being a neighbour from my village and he quite reasonably quickly devised a framework using steels,which take up a lot less room and is infinitely stronger and in some places lighter than the timbers it replaces,basically what is left of timber is really just batoning on the steel, the steels are through bolted on spread plates into the wall plates and supporting walls metal to metal through the timbers, and triangulated at each joint,I would guess that one or two of the 16 steel open trusses would offer equal or better support than all the timbers that made up that section of roof,(metal being my working material,saved me a fortune too even using a slightly heavier gauge metal than specified and adding more fixing points)the buildings inspector was more than happy and for me personally,after walking on the roof I have to say it feels incredibly solid👍,it was a real pain to accomplish but gives you the maximum space,there are companies building bespoke kits, but as I stated steel is my thing.
Is there a reason for taking the purlin out? I'm currently doing my own loft conversion, and was looking at leaving the purlin in and then putting a glulam beneath to take the new floor
Often it gets in the way, but you can leave it in if you wish. Most of the time they are greatly under-sized for the load so aren't doing what they are supposed to. I'd say 8/10 times that's the case with old roofs.
Thank you, that was very useful. I have no tie at the top but was going to add one anyway to provide a "flat" ceiling instead of a point.
HOWEVER, my issue is not the Purlins - I don't mind them - but I have Purlin "supports" at the mid way point which come down on the diagonal to a central point in the floor (over the central load bearing wall).
As your roof had no purline support at all - how vital are the supports in a typical 150 year old terrace house? I realise you cannot give "advice" but I would be interested to know of options - as other than the supporting wall which runs down the centre of the roof, under the apex, there are not other STRONG load bearing points of the floor - just "ceiling grade" joists.
I note the steel supports in your design above, but is SEEMED they were simply placed on the joists - which, as mine are just designed to "hold up a ceiling" and not be a floor, I am guessing are not strong enough.
Happy to keep the purlins, but would love to be able to get rid of the two purlin-supports.
Hi. The purlins in my video are supported, it's just not always shown because the video shows only a small section of the roof. You can't remove the props unless you support the purlins in some other way. The way I have shown in the video is with a flitch beam. A steel UB section is more usual.
Awesome, thank you for that. I will see what sort of costs are needed to do that :)
How would you suggest preparing rafters for a double velux (or similar) roof balcony window?
Hi Lee. This method would work well with a velux balcony 👍You would need to provide extra rafters to trim out the window.
Hi Robyn just a quick question. My loft is the exact same as the one in your video, with a wooden purlin either side of the loft running along the length and into either side of the wall. My question is would it still be possible to remove one of the purlins if it were adjoined to another house, as my house is a semi detached? So I’m not sure if the purlins will have any structural effect on next door also? Many thanks
Hi Ryan. Usually they are seperate purlins for each house, supported next to each other on the party wall. Can you see next door's purlin sticking through?
Hi Robin no you can’t. You literally just see the wall at each end. Nothing more.
Not sure I like the solution. Those old rafters often are an odd size and the bending moment are not great with regard to modern codes. The preferred solution is to put in. ‘L’ metal supports on each of the rafters and employ the stud wall you showed. For added safty the tie at the apex should also be put in place. These old buildings would never meet the snow load or wind shear for modern code. Hence to bring it upto Standred a solution like the one I have suggested may be considered. If you have gable ends I would put in a steel bean at the apex rather than the tie at the apex as a solution. What’s your view on my suggestion?
Do you need to do something to support the flitch beams on the ceiling joists now they are supporting the roof as well as the new storage floor?
The flitch beam is supported on the gable walls and internal wall.
@@RobindeJongh That explains it! Thanks
I have something similar to the end of the video. Vertical timbers connected to side of joists / rafters and collar ties between rafters. However, my collar ties are just above where the verticals connect. The verticals meet rafters 1.55m above the joists and the bottom of collar tie is at 1.75m. Apex of roof is 2.82m, outer walls are 8.2m apart and there is a central supporting wall. It's 3.6m between the verticals which is sufficient width for me... Would just want more headroom so would like to raise or eliminate the collar ties. It's been suggested to me that they could eliminate by adding bracing with some sort of steel plate / strap where end of joist and rafters are connected. (The joists sits on inner wall of cavity wall which has a 50mm wooden plate on top; the rafter is nailed to side of joist and is birdmouthed on to outer wall. It has no contact with inner wall). Can you maybe do a video about whether raising collar ties is possible / method?
Loft length is 16.4m so I'm assuming any solution involving gable to gable beam would be expensive/difficult.
To lift your collar ties you just need to be sure the rafters can still span the new longer distance without sagging. If the additional length of unsupported rafter threw you just over the span found in rafter tables you could always double them up from the vertical supports to the ridge.
Is that sketchUp?
Talking of equal loads, how does putting solar panels on on slope of the roof affect that? It seems to me it could make the load unequal and damage the roof
Depending on the weight of solar panels, it could cause the ridge to bow sideways and purlins to sag. The installers are supposed to have the roof assessed, I think.
I would strongly recommend providing a top plate over the dwarf wall, birdsmouthed into the rafters to provide a horizontal bearing interface. Otherwise your nailed rafter/stud connection needs to resist the slip force that is occuring in the inclined interface (I doubt you will be able to prove a nailed connection for such a load) in order to transmit the vertical load it needs to. I have never seen or specced a loft conversion as shown in this video. Also, for the ties would be against the side of the rafters, typically bolted or coashscrewed, not in-line.
Finally, much more common than having to maintain the ceiling span (which would limit the ceiling height) is to double up the long span of the rafters (in which case a top plate on the dwarf wall is essential so they have something to land on).
I don't want to bash the video, but whilst it looks nice it seems to lack a bit of practical reality IMO - don't rely on it as your only guidance if DIY-ing your own loft conversion!
Hi Martin. As mentioned in the video, I agree that a top plate is preferable. The uprights shown in the video wouldn't be just nailed - they would have nailing plates - but I felt the video would be too long going into that. Any loft conversion in the UK will need building control approval and structural engineer calculations.
Ive always wondered if old ( dry ) rafters are less flexible that originally calculated for in victorian rooves.
Hi Simon. The timber used is probably much stronger than the current timber, but that doesn't answer your question 🤣
Seen atleast 3 Attic conversions.
Only 1 has ZERO Sag (No Tramline in Tiles)
Purlins left in and More Height and Width.
Purlin adds as sloping window ledge for Emergency Escape Window.
Carpet the Purlins to stop Headaches.
Nice!!
Hi great work and love your content. As a builder I could do with this software😊 what is this software. Thanks
Try solid works,.... and 5 years at tech college
🤣 Well said!
Hi. It's SketchUp Pro. You'll love it! geni.us/sketchup
I have a wooden beam running across from one perlin to the other, is this normal? How can I remove without compromising structural probloms
Yes this is normal. You would need a structural engineer to design a solution.
What software is that?
Gracias
Do you do structural consultations and how do people contact you?
Contact me here for consulting work: geni.us/z5IzPej
Given that the loading force is at 90° to the rafters, how can the short supports from the flitch beam carry that load ?
Surely they will just give in the direction of that 90° vectored load direction ?... they are certainly not in compression to any real degree...
Or am I missing something here... 🤔
Hi Peter. The supports form a triangle with the rafter and ceiling tie.
How are you accounting for the exterior forces from, say, weather pushing on the roof? It would seem to me, uneducated in structural engineering that the purling provides a far greater resistence to the sheer force in the X axis of your grid drawing caused by gale force winds. Your vertical additions provide no support for sheer, nor do the span links at the top.
Does this not compromise the roof's strength against weather?
Also. You are removing an 8x2" beam and replacing it with some 2x4 uprights held up by cieling joists? You mention steel beam, please tell me there is a least a steal I beam across the ceiling now holding the roof up
Hi Paul. You're not the first to ask whether there is a beam! Yes, there definitely is. See the next video in the series for the full design: ruclips.net/video/jQ_u4dVobGs/видео.html
What's the name of this software??
The tie only works for balanced loads.
Heavy snow on one pitch, or high wind could skew the roof structure. This will dislodge the moisture membrane and tiles over a period if time.
If you add structural ply or plasterboard, the load is increased.
Get an engineer consultant to produce a solution with more rafter or cross bracing instead of tie.
This is why loft extensions carried out by jobbing builders leave long term problems.
Hi Mark. Absolutely, all loft conversions need a structural design. However I disagree with your point about the tie. As I said in the video, there is no additional plasterboard load in this case. Even with one sided snow loading the rafters still perform, because there is far less bending moment due to the tie. Try analysing this in a 2d frame analysis package and you will agree with me I'm sure 👍
What if the purlin is supported by a stack of bricks?
If you fix enough matchsticks together you get a strong structure.
Prefer the victorian roof I have, stood the test of time.
Never heard it called a flitch beam before.
I always called a timber running at right angles to the ceiling joists a binder.
Flitch beam is a 2-ply timber with a full span steel in the middle
Back in the day, we were only allowed to use steal siting on padstones for a suspended floor.
Everything must also be fire checked.
Dispite building regs, oftern it came down to building inspectors interpretations of the regs.
Hi Billy. Thanks for your comments 👍You're right, a steel beam is more usual.
What is supporting the flitch beams?
Hi David. See the previous video here ruclips.net/video/xDddwHq68QE/видео.html
@@RobindeJongh ah, ok, makes sense now I can see the full plan
Or you install deeper rafters for lofts with not enough head room.
🏠The next video in the series has just dropped! ruclips.net/video/jQ_u4dVobGs/видео.html
What’s the software thanks
Hi Ronan. It's SketchUp Pro - check it out here geni.us/sketchup
Excellence
Interesting
Basically form a stud wall and add ply
It becomes a structural panel and stops the studs wanting to deflect
😱Never do this unless the panel is supported on walls and has been designed by a structural engineer as a "box beam".
I thought the Flitch beam should ( or could) sit on top of the floor joists ONCE they have been upgraded from 4 by 2 to 6 by 3 ?.
Obviously I'm not a chippy.
Hi. The flitch beams are supported by the gable walls and internal wall. The new floor joists are supported on the flitch beam.
@@RobindeJongh ok cheers 👍 as a sparky I am sure ive seen it the other way round whilst crawling through loft conversions!! I may be wrong 😎
Robin where are you based thanks
Hi Margaret. The United Kingdom.
@1:40 your bending moment diagram is incorrect - as the rafters are continuous over the purlin the BM diagram should have a smooth midspan crown shape and two points of contraflecture (one either side) not a pointed peak.
@1:50 In addition the BM would only be 4x as much if the span was doubled, but with long span each end is restrained in position only whereas the short span the ends at the purlin are restrained in position AND line. Therefore the EFFECTIVE length of the short spans are 0.85L ….. BM for UDL is WL/8x0.85 not WL/8 (simply supported case)
Hi. The bending moment diagram is correct. The first diagram shows the purlin support at midspan, and the second shows it removed. Please check using the free Skyciv beam designer and see if you agree 👍
If I missed it but no mention of noggins or sheathing to make that new wall a structural stud. Also the tie in the top half ain't cutting the span so not to sure on the facts ypu out across
Hi Tarique. Thanks for your comment. Can you explain further what you mean by "cutting the span"?
If you use a steel truss system you can eliminate the uprights.
A steel ridge would have helped.
absolutely no need for any of that. remove the perlin and wait until the first stronger wind or winter with snow, and the roof will realign itself on the ground or on the floor of your living room, at that time you have plenty of storage space and a nice view to the night sky :) (provided you werent in the building when the “realignment” happened :)
lot of work for about 35 cm more width
Hi John. The reason for it is to strengthen the floor and roof to allow for storage or habitable space. You can then also create a velux opening.
Don't take purlins out after watching RUclips.
Hi Joel. Thanks for the warning. Yes, of course it goes without saying that all structural alterations need a structural engineer and building control approval.
I totally disagree with what you did here , in a short length of building you could get away with it but you are moving the point of support , ridge moves down and the walls will bulge , no matter how well you think the rafters are tied at the base you have added load there from the purlin you took out
Hi Philip. The flitch beam (or steel) takes up all that load.
That’s wrong it needs to be a H beam DONT do this it’s Wrong
Hi. It can be a glitch beam as shown, or an “H” beam. Either would need structural calculations and building control approval.
@@RobindeJongh I’ve put loads of them in mate Master bricklayer
@@thewhiteworkingclassman7471 So you'll have used a structural engineer for each of them I trust.
@@RobindeJongh just put a video up of us putting the steel in for the floor to sit on
@@RobindeJongh just put one more up for you to look at mate are you a builder?