Thread: Roof framing birdsmouth

Hi Mark. It is quite an involved process .You also need a copy of the Hancock's Roofing book.This is a guide that carpenters use to aid them with these calculations.There are plumb cuts as well as side cuts to consider.It isn't just a measurement that can be calculated.The birdsmouth cuts are a lot "flatter" on the hips than the rafters. Hope this helps. Tony.

Like tonymarten, I also would use Hancock's to work out the angle's of the cuts, though there is probably a mathematical way of doing it (obviously). As far as pragmatic relationships go, the vertical height from the edge of the plate to the top edge of the hip must equal the height from the edge of the plate to the top of the rafters (and creepers). ie they must all be (or end up) in the same plane.
Hope that doesn't confuse things too much.
TM

What about doing a scaled drawing by hand ? Graph paper and a scale rule would be helpful but not essential.

Thanks for your input guys. I think I worked it out. I can use trig to work out all the lengths and angle cuts, it was just the relationship between the hip and the rafter that I could not work out how to accurately calculate the hip birdsmouth when the sections of timber are different and keep the tops on the same plane as tony & termi correctly pointed out. I had to consider the width of the hip because of where it sits on the top plate and also the difference in heights of the rafter and hip, just making a little excel program, similiar to blocklayers.I hope to have a program for broken hip roofs etc. eventually, maybe its just been raining too much and I am bored. ha ha