Steep roof rafter sizes

[Benpointer]

Hi there, does anyone know where I can find rafter size guides for steep pitched roofs? The only TRADA ones I can find talk about 30-45 deg max.

I am looking to build a large A-Frame potting / storage shed, based on two 3-4-5 triangles back to back, so the pitch is going to be about 53 degrees. The A-frame span will be circa 5.4m, with the bases bolted to a concrete slab, so the rafter lengths will be about 4.5m, with a ridge height of 3.6m. I intend to support the rafters with a supported purlin at their mid-point. I want the rafters at 600mm centres and the roof will be tiled with plain clay tiles.

If anyone knows what size rafters I can get away with that would be great. Or am I ok just to use the 30-45 degree tables?

Thanks

 

[RobinBHM]

I would assume that the load decreases as the pitch increases, so using the 30-45 deg calcs should be fine.

Also steep pitch roofs have reduced snow loads.

I guess though the wind load will increase as the pitch increases

There are a few structural engineers on this forum, so Im sure you will get a more qualified reply

 

[skipdiver]

I use my local councils website, which has a rafter span guide and i would imagine most council sites do. They don't list anything above 45 degrees but as Robin says, the load decreases as the pitch rises, so yes, you are ok to use the tables for 35-45 degrees.

 

[Benpointer]

Great, that's what I will do then! Thanks guys

 

[MikeG.]

I hope the author has already found the soultion, but I want to share my experience, because recently I've faced the same issue. Like most people I started my search using Internet Of course, it took me some time to find all necessary information, but it was worth it as I discovered an online roof rafter calculator (if you are interested, it is possible to find it here). Personally I think it is very convenient that I can calculate rafter lengths being at home. I hope this information will be useful and helpful for someone!

Just a word of caution here......that looks like an American website, and they don't have the same Regulations (they call them Codes) as us. Further, these online calculators won't be accepted by Building Control as evidence that the roof is properly designed. So, if you are involved with a roof which is required to meet building regulations, then don't rely on this calculator.