How to Make & Mount Trusses on a Shed
- 1). Design the shed roof truss based on the width of the shed and the pitch or slope of the roof. Calculate the rafter run, the distance each rafter on the truss must support from peak to wall, by dividing the width of the shed in half -- the run on a 10-foot wide shed is 5 feet, for instance. Use a medium pitch, like 4/12 or 5/12, slopes of 4 or 5 inches per foot of rafter run.
- 2). Make one rafter as a pattern to cut pieces for all trusses. Lay a 2-by-4-inch board flat with the 4-inch face up. Put a framing square at one end, with the thin tongue on the right facing up. Align the point of the square at the bottom of the board with the 4-inch mark on the tongue for a 4/12 roof and the 12-inch mark on the wide blade at the top of the board. That forms an angle at the end of the board, the top or plumb cut for the roof peak.
- 3). Use the "common rafter" table on the square's blade to figure the length of rafter needed from peak to wall. That's 12.65 under the 4-inch mark for a 4-pitch roof, or 12.65 inches of rafter for every foot of run. Multiply that by the run -- 12.65 times 5 on a 5-foot run, or 63 1/4 inches. Use a tape measure to mark that distance on the bottom of the board from the bottom of the plumb cut. Draw a line with the square 1 inch into the bottom of the board. Measure 3 1/2 inches back up the board with the square and connect that point with the top of the vertical line to mark a bearing point, or birdsmouth, to fit over the wall. A birdsmouth is the term applied to the triangle notch that fits on the wall top.
- 4). Add a foot to the rafter for an overhang on the side of the roof. Mark an angle at that point, the reverse of the plumb cut, by putting the point of the square at the top of the board. Cut those three angles with a circular saw. Test the rafter by setting the birdsmouth on the top of the wall with the plumb cut in the center of the roof. Cut all other rafters to that pattern. Determine the number needed by dividing the length of the roof by 24 -- the inches of space between trusses -- and multiply by two for a rafter on each side of each truss.
- 5). Lay two rafters on a flat surface, like a driveway, with the plumb cuts together. Measure between the vertical line of the birdsmouth on each rafter to make certain it is the same dimension as the wall --10 feet for a 10-foot roof. Connect the peak where the plumb cuts meet with a gusset, a plate that overlaps the peak and fastens to each rafter. Use purchased metal gussets or cut gussets from plywood to conform to the peak and go across both rafter tops. Fasten the gussets with framing nails and a hammer.
- 6). Set a 2-by-4 between the truss rafters horizontally 8 inches down from the bottom of the peak. Mark the angles of the rafters on the end of that board, cut it to fit and install it with gussets on each rafter. Be certain this cross tie is perfectly horizontal. Turn the truss over and add gussets on the other side at each connection point. Build all trusses the same.
- 7). Mark truss locations on both wall tops. Use the tongue on the framing square to draw a line inside the end for the first truss. Measure 23 1/4 inches from the wall end and mark the end line for the second truss. Use the tongue to mark that space, 1 1/2 inches. Use the blade to mark rafter lines 24 inches apart the length of the roof; the last space may be slightly less than 24 inches.
- 8). Lift the first truss to the roof, erect it plumb with a level and secure it with framing nails and a hammer. Set all other trusses in place at the marked locations and nail them to the walls. Install "gable studs" on each end truss, 2-by-4s cut to fit between the bottom of the cross tie and the wall top; toenail these in place with framing nails driven diagonally. Add "hurricane clips" to each truss on each wall; these are metal brackets fastened to truss rafters and wall boards to hold them together.
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