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- 4 Dec 2021
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New to group and looking for advice on birds mouth cuts on sloping rafter roof.
roof 1
Mono pitched roof. Span is 4.37 m (measured on slope) pitch is 15 degrees, it is a open from floor level to underside of rafters ( ie relying on solely on rafters to hold masonary walls at each end, no ceiling ties etc). Rafters have been sized using trada tables at 195 x 47 c24 at 400 centres. I’ve actually used 225 x 47 as overkill. They sit on top of wall plates on inner leafs at both ends. My question is how deep can I cut birds mouth into the timber??, I’m thinking 75mm, third of overall timber height???.
roof 2
Pitched roof, peak being supported on steel ridge beam, rafters bolted together over top of ridge beam. Timbers again sized using trada tables come out at 100 x 47 c24 at 400 centres. As rafters are bolted together over ridge beam this will eliminate the sideways force on masonry walls at wall plate ends, again I’m thinking 33mm, third of overall timber.
ive seen examples of birds mouth being cut where the seat cut rather than coming flat out to underside of rafter is sunk down into rafter itself. A large chunk being cut out rather than a triangular shape, using a heal cut at either end of seat cut
any advice welcomed
roof 1
Mono pitched roof. Span is 4.37 m (measured on slope) pitch is 15 degrees, it is a open from floor level to underside of rafters ( ie relying on solely on rafters to hold masonary walls at each end, no ceiling ties etc). Rafters have been sized using trada tables at 195 x 47 c24 at 400 centres. I’ve actually used 225 x 47 as overkill. They sit on top of wall plates on inner leafs at both ends. My question is how deep can I cut birds mouth into the timber??, I’m thinking 75mm, third of overall timber height???.
roof 2
Pitched roof, peak being supported on steel ridge beam, rafters bolted together over top of ridge beam. Timbers again sized using trada tables come out at 100 x 47 c24 at 400 centres. As rafters are bolted together over ridge beam this will eliminate the sideways force on masonry walls at wall plate ends, again I’m thinking 33mm, third of overall timber.
ive seen examples of birds mouth being cut where the seat cut rather than coming flat out to underside of rafter is sunk down into rafter itself. A large chunk being cut out rather than a triangular shape, using a heal cut at either end of seat cut
any advice welcomed
