Why does a stick built roof system have a bird's mouth cut into the rafter and a truss doesn't?

Answer 1

A truss is built with a flat spot where it bears on the exterior wall for positive nailing and load dispersment.
A stick built roof has to have a bird's mouth cut into it to achieve the same positive bearing and nailing.

Answer 2

A Stick built- must have the Bird Mouth to cut the Rafter level or Plumb cut to set level on the Wall- and the Joist sets beside it- A truss, the Rafter part sets on the Joist, and the Joist part is flat to the Top Plate already.

I have toyed with the idea of just cutting an Angle on the Top plate so the Rafter lays flat on the Angle, seems easier than cutting all those dam Bird mouths. lol

Answer 3

In a truss roof, the ceiling joist is part of the structure of the truss. The whole assembly can just bear on the top plates.

In a stick-framed roof, the rafters are connected primarily to the top plates, not the ceiling joists. The birds mouth gives the rafter an adequate bearing surface on and attachment point to the top plates.

Answer 4

a truss has a bottom chord piece of lumber that sits flat on the load bearing walls. the stick built roof has the rafter running from the outside wall to the ridge and the birds-mouth cut prevents the rafter from sliding off the wall,also provides a secure foot hold for the rafter

Answer 5

trusses have a lower plate that you nail to the wall plate stick built roofs need a flat spot to nail to other wise they will slide of under the weigh of the roof

Answer 6

Well, it's like this. A bird needs somewhere to sit after flying all the way across town. And when there, , , , oh crap, I don't have any idea, but I did stay at Holiday Inn Express last month with my parents.

Answer 7

mass production of trusses make details like this complicated and costly to execute.

Answer 8

i dont know