Did you know how a roof structure works in the UK?
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- Опубликовано: 20 дек 2022
- Take a fully illustrated tour through a traditional rafter and purlin roof, learning how each element works. The video covers common rafters, ridge board, purlins, ceiling joists, ceiling binders, and placement of supporting walls. We look at how the forces work and the most critical part of this roof that many people forget!
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I am a Chartered Civil Engineer with a specialism in Structural Engineering. While I try to be correct and to present useful information, this video is just for entertainment and educational purposes. You will need to seek professional help on your individual project:
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This is a very interesting video with good ideas. I am from the U.S. and it seems there are different practices in carpentry here. The idea of supporting a rafter with a Perlin at the mid-section is new to me. I will consider it. Thank you for sharing. And you have a new subscriber.
Excellent video as usual
Most Roofs now have double wallplates as joists are mainly standard 9 inches
Also nearly all new build specifications ask for RSJ as purlins with wallplate bolted on top to nail rafters due to excessive spans
Thanks for posting your videos, mighty stuff
Great video! Thank you!
Great video, many thanks Robin. Interesting to look further at some of the fixing details and things like purlin ties, and how you might go about repairing old brittle timbers. For the ceiling joists you need good overlap at the nailing point which is easy in the centre, but limited space at the eaves, so wonder if some form of brackets might be better there than plain nailing. Also consider the gable walls - the purlins provide the longitudinal bracing, but what about diagonal bracing - assume the intermediate purlin support walls help with that? Many thanks again.
I have ceiling binders which I understand shorten the span that the ceiling joists have as they sit on the external in internal supporting walls. Are they normally just nailed through to each joist or should they have blocks which get nailed to both joist and binder? Or can you use the a thin metal tie? I assume they stop the joist bowing downwards under the weight of the ceiling plasterboard since they are under tension as apposed to having any vertically downward force upon them?
If you have purlin do you need collars ? Doing an attic conversion and currently there are purlins and collars but I need to get more head height. I was thinking about using 90degree amgle steel brackets to attach the rafters to the purlin and do away with the collars all together. Any views would be appreciated
Thanks for uploading all your helpful videos. I am struggling to understand how to calculate the load that the purlin carries. I appreciate it will depend upon the pitch of the roof and that the bulk of the load will be transferred by the rafters to the external walls. However, how do you calculate the load that the purlin needs to be capable of carrying to provide the necessary stiffening to the rafters without deflecting?
I have been unable to find anything on this on the internet.
Hi Mike. I recommend my timber beam video, ridge beam video, and timber beam deflection video. Let me know if you have trouble finding them - they should be on the channel home page.
I have this type of roof and want to raise the joists to make a higher ceiling. Is this not something easily done with this kind of roof?
The graphics software gives a very good visual representation of the construction, what software do you use for this?
Thanks Pearse. It's SketchUp Pro - see geni.us/sketchup
I think I have heard the load bearing wall in the attic being referred to a dead man wall in the past
Nice video. at 0:34, Is the ceiling binder the same thing as a strongback? Is it's purpose to keep the ceiling rafters from twisting? If the roof joists are in parallel with and connected to the ceiling rafters at the wall plate, then the ceiling rafters would be under tension. What would cause them to twist?
Hi Claude. The ceiling binder supports the ceiling joists if their span is too great, to stop them sagging.
My bad. At 2:35 and 4:19, you explain this. I suppose a strongback can be used as a ceiling binder. (For example, a vertical 2 x 6 to which a horizontal 2x4 is nailed, and the 2 x 4 is nailed in perpendicular to the ceiling joist). Again, thank you for an excellent video. @@RobindeJongh
Great explanation.👍
I have an issue with my roof that requires some expertise to remedy.
Is this something you would consider please?
Alan.
Hi Alan. If you have drawings or photos we may be able to help.
@@RobindeJongh that would be great! Thanks Robin.
What's the best way to contact you?
Hi Alan. Consultancy request form forms.gle/ooxdhbUT6ku4jBkP9
what keeps the masonry wall from deflecting due to wind forces ? is it act as a cantilever ? because the triangle roof cant act as a support...
Good question! The ceiling acts as a structural diaphragm to resist wind loads from the walls, and transfer these loads to the perpendicular walls.
@@RobindeJongh yes but the ceiling is made of the ties from the triangle. i know that you have a diaphragm on the floor below.
meaning groung floor and roof.
Both ceilings act as diaphragms if they are plasterboarded.
The binder typically does not half the ceiling joist span - if you run a calc you'll find most binders are nowhere near able to span the distance with the load they would need to take. What they primarily do is bind the joists together, such that if you were to point load one joist (i.e. by standing on it) it spreads the load to adjacent joists which a) helps reduce overall deflection, but perhaps more importantly b) prevent excessive deflection of the joist being stood on relative to the adjacent joists, as this sharp change in joist level would likely damage the ceiling finishes under.
Binders also help provide lateral stability to the ceiling joists, and in hipped roofs can do double duty in acting as ties to prevent the wall supporting the hip rafters from spreading.
Assume the binders also help stop the joists from twisting and make everything more rigid?
@@johncoppock3823 Absolutely, that's what I was referring to with lateral stability (Engineer jargon!).
@@smartbuildengineering Many thanks Martin. I am a CEng but the wrong discipline. I really like structural engineering in that what you see and imagine up is what you've got, so its down to the grey matter, not guessing what you are looking at from secondary effects etc.
Great vid! If the ceiling ties are no longer there do the purlins help stop spread by reducing the rafter span?
Not really.
If you were to basically turn those ceiling joists into a floor by nailing a board on edge around the perimeter, then you add another plate on top of that, what, if anything, has to change when doing a gable roof? Your rafter wouldn't be connected to the ceiling joists but would that even matter since your ceiling joists are tying your walls together? Here's the video I'm referencing. It's in the second half of the video. ruclips.net/video/ceGKy_1VwOk/видео.html
Hi Joshua. There's other ways to do this, as you have mentioned. I've shown the typical way that homes are constructed in the UK, if trussed rafters aren't used.
Great video with clear explanation, but I'm not sure I understood the final point. My house roof has vertical purlins with vertical strips of wood nailed to the rafters and ceiling joists running alongside the inside of the purlin. Are they to support the roof, or ceiling below?
I have the same in my roof and I believe it's to supporting the ceiling joists. I do feel like this video ended abruptly, I thought he was about to explain the link between the ceiling ties and purlin orientation. Great video still, absolute treasure trove of information and so well explained!