Birds Mouth on roof rafter

[couldidoit]

Hi,

Installing a new roof, the pitch is 35° and the roof rafters are 150mm wide. From what I have read the birds mouth should be 1/3 into the rafter. Does that mean 50mm or 1/3 of what the plumb cut would be 183mm therefore 61mm.

Thanks

 

[garyo]

It doesn't matter - using either measurement you'll get the same depth, because you're measuring at different angles, if you see what I mean.

 

[couldidoit]

Thanks for getting back to me. As I wrote the question and visualized the measurements I thought that, in fact after posting the question I went and drew it on a piece of paper with the bird mouth at 61mm plumb and then measured the shortest distance from the corner of the birds mouth to the edge of the timber (drawing) and sure enough approx 50mm.

Perhaps the question will help somebody else in the future if they search for birds mouth.

Once again thanks

Ian