Rafter cutting

woody7777

I am going to change a small flat roof to a pitched one on a porch. Does anyone know how to get the angle of the cuts, and where the birds mouth cut will go in distance from the end of the rafter?

grumpy_codger

The angle depends on how you measure it. It's 90deg +/- pitch.
For the distance use either Pythagoras theorem or trigonometry. It's the hypotenuse of the right triangle. 

stuart45

If you tell the the pitch e.g. 35 degrees,  the span measured from the outside of the wall plates, ridge board thickness and overhang length I'll give you the dimensions.

woody7777

The span will be 2.4M. The ridge 25mm and the overhang 150mm. The pitch will be 30. The rafters will be 150mmx50mm. 

Bookworm105

just watch a You Tube video, there are loads that show you exactly what to do and various methods by which to get there 
birds mouth cut for rafter - YouTube

john.h

Try here https://www.blocklayer.com/roof/rafter