I'm replacing a the roof on a 100 year old extention to my house. The present purlins are 7x3 inch. The length is 4.6 metres and the rafters are 3 metres long at roughly 45 degrees. Can anyone advise on a suitable size for replacement purlins please?
size of purlin?
- Thread starter calvert
- Start date
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will the purlin be supported mid-span?
or, you could use 6" x 3" rafters and do away with the purlin maybe?
we recently installed 75mm x 200mm C16 purlins over a similar span but these were supported mid-span either by steel and 100mm x 100mm props or masonry.
or, you could use 6" x 3" rafters and do away with the purlin maybe?
we recently installed 75mm x 200mm C16 purlins over a similar span but these were supported mid-span either by steel and 100mm x 100mm props or masonry.
There is nothing to support them midway. The old rafters are 3x2 and I was hoping to use 4x2 C16 as I happen to have quite a lot. Rather than instal ceiling joists and a conventional ceiling I would like to have a vaulted ceiling and have teh purlins as a feature. If this cannot be done, could I use say,a 7x2 ridge board (I'm thinking about the roof sagging and pushing the walls out. By the way, the tiles are old clay double romans.
Put a ridge purlin in, span the rafters from wallplate to ridge and bird beak over both, then there's no risk of spread. That way, you can put a purlin in as a feature, of any size you like, as it won't be doing anything other than looking pretty.
Now you just need the size of a ridge purlin...
Now you just need the size of a ridge purlin...
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Oh why do I do this, I have customers who pay for this kind of info...!
Ok, give me:
Ok, give me:
- span from eaves to eaves
span of ridge purlin
roof pitch
roof covering
Thats very kind of you. Distance between eaves is 4.8 metres. The span of the purlin ridge is the same. The roof angle is 45 degrees and the covering is clay pantiles (Double Roman, they call them round here but I don't know if that is a just a local name.) I hadn't thought of anything but timber. I presume the flitch beam would be smaller dimension so lighter to handle, but more expensive. Or am I way off the mark with that guess?
You're very trusting, you don't know who I am or what I do! However, I am a chartered SE, so I'm not blagging it, honest
You need 2/50x225C24 timbers with a 10x225 mild steel flitch plate sandwiched between, bolted at nominal 600 centres mid depth along the length, with 2M12 bolts vertically at 1/3 depth over the supports either end (ie 50 in from the end of the beam. Engineering brick padstone under the beam either end.
Alternative in just timber is 4/50x275C24 bolted together M12 at 600 along the length - that size of timber is probably difficult to get hold of, though.
Steel alternative is 178x102UB19 with 100x50sw plate coach bolted M10 to top flange at staggered 600 nominal centres.
Rafters 50x125C24 at 400 centres, bird beaked over wallplate and ridge beam.
Add in any size of purlin that you want, purely as a feature.
Thank you and that will be £150 plus VAT please
You need 2/50x225C24 timbers with a 10x225 mild steel flitch plate sandwiched between, bolted at nominal 600 centres mid depth along the length, with 2M12 bolts vertically at 1/3 depth over the supports either end (ie 50 in from the end of the beam. Engineering brick padstone under the beam either end.
Alternative in just timber is 4/50x275C24 bolted together M12 at 600 along the length - that size of timber is probably difficult to get hold of, though.
Steel alternative is 178x102UB19 with 100x50sw plate coach bolted M10 to top flange at staggered 600 nominal centres.
Rafters 50x125C24 at 400 centres, bird beaked over wallplate and ridge beam.
Add in any size of purlin that you want, purely as a feature.
Thank you and that will be £150 plus VAT please
Correct - in floors, for example, where shrinkage may be an issue and the plate ends up dinking the floor or ceiling finishes. Not a problem up as a ridge purlin, hence no need to make it 25 less depth. you think I don't think of these things???!
you think I don't think of these things???!
Well I have to check these little details, to make sure.
I'd still have deeper timbers though
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