I'm about to start on my new shed. The roof will be a flat roof with EDPM over OSB3, so needs a minimum fall of 1:80. I've designed the building with a fall of 1:40 to be more forgiving of any inaccuracies I build in. I was also planning to use upside down joist hangers tying the roof joists to the header plates to add strength against aerodynamic lift.
Question: Is it ok to NOT cut birdsmouths on a shallow fall such as this? The bearing of joist on header is going to be 100mm, so at the deepest point the cut will be just 2.5mm... about the kerf of my circular saw. I'm not convinced I could accurately cut wood with such a shallow angle of attack. Also I've seen plenty of garden room builds on YouTube with similar falls that leave them out but not got first hand experience.
I know I could get firring strips cut at such an angle, but whenever I have seen them used they seem to have split at the thin end once the sheets are nailed down.
Question: Is it ok to NOT cut birdsmouths on a shallow fall such as this? The bearing of joist on header is going to be 100mm, so at the deepest point the cut will be just 2.5mm... about the kerf of my circular saw. I'm not convinced I could accurately cut wood with such a shallow angle of attack. Also I've seen plenty of garden room builds on YouTube with similar falls that leave them out but not got first hand experience.
I know I could get firring strips cut at such an angle, but whenever I have seen them used they seem to have split at the thin end once the sheets are nailed down.
