Hi, building a small extension to the rear of my property, now up to wall plate hight and unsure as to what the regs are regarding spec of timbers I need? The roof is monoo pitch with a shallow fall, width 2.9m, length 4m. Does it require a purlin and if so what size, also what size will other timbers trusses etc need to be. I would appreciate any help on this.....
mono pich roof
- Thread starter notnochippy
- Start date
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A 3.2m clear span (rafters) would require a rafter size of about 175mm x 50mm at 450mm c/c, so no need for a purlin.
The ceiling joists would probably come out at 150mm x 50mm.
You will need a pitching plate and a pole plate for the rafter and joist abutments which could be say 150mm x 50mm, stagger bolted every 600mm.
The ceiling joists would probably come out at 150mm x 50mm.
You will need a pitching plate and a pole plate for the rafter and joist abutments which could be say 150mm x 50mm, stagger bolted every 600mm.
Firstly many thanks for your reply noseall, unfortunately my lack of knowledge on roofing has led to not using correct terminology refering to length and width instead of span? the span is actually the larger dimension 4m so am I right in saying that this alters your response? If so how??
If you want to do 4m in a single span you will need 200x50 joists at 400mm centres.
Ceiling joists can be 125x50 (if no room for storage), 150x50 if you'll have a loft hatch.
If you did decide to use a purlin it would need to be something like a pair of 200x50 timbers bolted together, then the rafters could be 100x50 timbers, but don't see any benefit in doing it that way...
Ceiling joists can be 125x50 (if no room for storage), 150x50 if you'll have a loft hatch.
If you did decide to use a purlin it would need to be something like a pair of 200x50 timbers bolted together, then the rafters could be 100x50 timbers, but don't see any benefit in doing it that way...
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Okay, having done some calcs. I do definately require a purlin if nothing else it will keep the building inspector happy. problem is now how do I attach the purlin to the two sloping walls? Sure this sounds silly but I am a complete novice.
just one more thing. What bolts would you recommend to attach pitching plate to the wall. pitching plate is 4 by 3
A purlin rests on the wall and is usually bricked-in
A wall plate is bedded (using mortar) onto the top of the internal leaf of masonry and is secured with holding down (bent) straps.
A pitching plate is the rafter end support timber that is set below (or at the ends) of the tops of the rafters and is set to the vertical part of the wall when building a lean-to, mono pitch roof.
Make sure that the purlin is beefy enough so that it does not require any mid-span support itself.
A wall plate is bedded (using mortar) onto the top of the internal leaf of masonry and is secured with holding down (bent) straps.
A pitching plate is the rafter end support timber that is set below (or at the ends) of the tops of the rafters and is set to the vertical part of the wall when building a lean-to, mono pitch roof.
Make sure that the purlin is beefy enough so that it does not require any mid-span support itself.
great thanks for that, does the purlin need to be built in at an angle to match pitch of roof or square to blocks?
Build it vertical and birdsmouth the rafter onto it.
can joist hangers be used instead of birdsmouth?
You cut all the rafters, complete with b/m's, fix them into place then offer the purlin up to the b/m's, then fix it to the rafters.
You then build up the gables, thus securing the purlin.
You then build up the gables, thus securing the purlin.
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