Roof Framing Simplified
This direct approach involves full-size layouts and stringing rafter lines.
Synopsis: The author briefly explains two methods of framing a roof that do not involve mathematical calculations: snapping chalk lines on the subfloor and taking measurements directly from the roof. An accompanying glossary identifies various components of a framed roof.
There isn’t a cut in roof framing that can’t be calculated given a sharp pencil, a framing square and a head for math. But my 20 years in the trade have taught me that in some cases, the theoretical calculation of rafter angles and lengths is slower and leaves more room for error. While I think that it’s important to understand the geometry of roof framing, the empirical method can save time and frustration, and contribute to your understanding of the process. I’m better at solving problems when I can grasp them — literally.
When I’m cutting a complicated roof and things get foggy, I use two techniques to help me produce rafters that fit the first time. I chalk lines on the plywood subfloor to represent a rafter pair in relation to its plates and ridge. This two-dimensional diagram is laid out full size. Pattern rafters can be tested right there on the job site. The other method I use is to deal directly with the components involved by getting up on the roof and measuring the relationships between the rafter to be cut and the existing plate and ridge with string and sliding bevel.
I used this method several years ago when I built a Y-shaped house. One wing was for the bedrooms and the other contained the kitchen, dining room and family room. The stem of the Y was the living room. The roof over the wings called for trusses, but the living-room rafters were exposed. The problem was in framing the intersection of…