roof fall on a garden room

[Jupiter01]

I will have 15mm OSB, 1.2mm rubber roof, 70mm pir insulation and plasterboard.

 

[stevie888]

Can I also get some more views on whether the 5x2's will suffice for my roof or whether the 6x2s are an absolute necessity in my situation please. The rafters will be spanning 3 metres of the roof and have some overhang and I was going to centre them at 400. It will have a rubber roof on top of this.

See my post 2. It's a fancy shed at the end of the day and it's never going to get the snow load allowed by TRADA tables.

If you're really, really worried close 'em up to 300 crs. This will provide the same strength as notional 67mm wide timbers at 400 crs. TRADA lists 63s as ok to 3.1 clear span.

You don't need 150s, that's for sure

 

[Jupiter01]

Thanks guys. I am happy to 300 centre the 5x2s but crucially I need to decide now whether it will be 5 or 6 inch rafters as I am building the walls accordingly, and staying within my 2.5m height limit.

 

[chirpychippy]

I have to go by span tables because I have to guarantee my workmanship, but i agree with cbde and over engineering, there is little in it really. The span isnt the total span of the building, the span relates to the unsupported distance between the walls. The 5x2 in the span tables falls "slightly" short if you use C24, but its millimetres. If I had a height issue and wasn't building to regs I think I would use 5x2, but do put a row of noggins down the middle to avoid joist twist.

If it shows heavily just pop up with a broom.

 

[Jupiter01]

I have to go by span tables because I have to guarantee my workmanship, but i agree with cbde and over engineering, there is little in it really. The span isnt the total span of the building, the span relates to the unsupported distance between the walls. The 5x2 in the span tables falls "slightly" short if you use C24, but its millimetres. If I had a height issue and wasn't building to regs I think I would use 5x2, but do put a row of noggins down the middle to avoid joist twist.

If it shows heavily just pop up with a broom.

Broom LOL
Would you leave at 400 centre in my situation? Won’t hold you to it. Honest.

 

[Jupiter01]

With a 5cm fall on this roof and my other 3 walls being the same height, I envisage a small gap above the side walls and roof overhang. Given how small this will be, how do I tie the roof into these sidewalls?