How to Build 8-by-12-Foot Roofing Rafters
- 1). Decide on a pitch for the shed roof. That is the slope or the amount of rise from the side wall to the peak. Most sheds use a fairly small pitch, usually a 4/12 or 5/12. That means the roof rises 4 or 5 inches for every foot of run or distance between the wall and peak.
- 2). Make a test rafter from a 10-foot 2-by-4-inch board. Put the framer's square at one end with the angle point at the bottom of the board, the 4-inch mark on the short side of the square and the 8-foot mark on the long side at the top of the board. That will give you an angle to cut on the end.
- 3). Determine the length of the rafter with a table on the long side of the square. For a 5-pitch roof it will show the rafter needs to be 13 inches long for every foot of run. For an 8-foot shed that would be a 4-foot run or 52 inches from the peak to the outer wall. Mark that spot and measure an additional 4 inches. Cut 1 inch into the bottom of the rafter at the 52-inch mark and diagonally down to the end mark. That will create a notch to fit over the side wall cap. Add any overhang, the distance the roof will extend beyond the wall. That would be 52 inches plus the 4-inch notch and another 4-inch overhang, for a total of 62 inches. Cut the rafter that length, diagonally the same at the top end but reversed.
- 4). Test fit that notch to make sure it fits properly at the top and edge of the wall cap. Then cut another inch from the top angle to allow for a 2-inch ridge board at the peak. Cut another rafter the same and put the two on one end of the roof, with a piece of 2-inch board between, to make sure they fit properly on both walls and at the peak. Then cut five more pairs of rafters to the same pattern.