I need to know how to cut rafters for a plalyhouse that is 66 inches wide. I want a pitch of 8/12. I need to know how far back to cut the seat cut. Thank you.

Cut an 8/12 pitch on the end of a rafter. Then hook your tape and measure along the top of the rafter 39 5/8" and draw a parallel 8/12 plumb cut. From the bottom of the rafter, measure up along this plumb line about 1/3 of the rafter width and make a mark. From this mark on the plumb line use a square to mark a line 90 degrees to the plumb line. This is your seat cut/birds mouth.

How I came up with this number was run 33" (1/2 of building width) X the number on the framing square 14.42. On the framing square you will see a table for rafters. You follow the table under "common rafter" along until you get to the number 8 (8 pitch) It is 14.42.

So 33 x 14.42 = 475.86 divide this by 12 = 39.65" The closet equivalent to .65 would be 5/8" or 11/16".
So your rafter length from plumb cut to your seat cut would be 39 5/8"

There is software on the internet that does this for you and let's you decide the truss style for most efficient use of wood (based on roof load). Of coarse, your roof load would be negilgable. Search on the WEB you should find some free-ware.

Rafter length