- 1). Determine the width of the shed to calculate the rafter angles and cuts. The essential figure is the rafter run, which is half the width and the space each rafter must support. Decide a pitch or slope, expressed in inches per foot of run. A typical shed roof might use a 5/12 pitch, which is a rise of 5 inches for every foot from wall to peak. Use the length to determine the number of trusses, spaced 24 inches apart.
- 2). Lay a 2-by-4-inch rafter board flat on a level surface with the 4-inch side facing up. Put the point of a framing square at the bottom on one end of the board. Align the pitch mark on the thin tong, 5 inches in this example, and the 12-inch mark on the wide blade at the top of the board. Mark the angle that forms along the tongue at the end of the board with a pencil, for the top or plumb cut where two rafters meet at a peak.
- 3). Use the table on the blade of the square to calculate the rafter length. Look under the pitch mark; it shows 13 for a 5/12, meaning a rafter must be 13 inches long for every foot from peak to wall. Multiply the run, 5 for a typical 10-foot-wide shed, by 13, and measure that distance — 65 inches — with a tape measure down the bottom of the board from the plumb cut.
- 4). Mark a triangular birdsmouth to fit over the wall plate. Measure 1 inch up into the rafter board at the 65-inch mark. Measure back up the board 3 1/2 inches from that point. Connect the top of the 1-inch line with that mark for the triangle. Add an overhang, typically a foot, and draw another angle, like the plumb cut but with the point of the square at the top of the rafter.
- 5). Mark a triangular birdsmouth to fit over the wall plate. Measure 1 inch up into the rafter board at the 65-inch mark. Measure back up the board 3 1/2 inches from that point. Connect the top of the 1-inch line with that mark for the triangle. Add an overhang, typically a foot, and draw another angle, like the plumb cut but with the point of the square at the top of the rafter.
- 6). Use a circular saw to cut the angles on that rafter then use that rafter as a pattern to cut all others needed, two per truss. That would be 12 rafters for six trusses to frame a 12-foot-long shed, for example.
- 7). Lay one pair of rafters on a flat surface with plumb cuts aligned and birdsmouths spaced the distance of the wall cap. Place a 2-by-4-inch board across the rafters a third of the way below the bottom of the rafter peak and mark the rafter angles on it to form the cross tie. Cut all the cross ties.
- 8). Lay out a set of truss pieces, with rafters and cross properly positioned. Cut plywood gussets or connectors from 1/2-inch plywood to overlap the three joints where boards meet. Make the peak gusset straight across the bottom and slanted at the top at the rafter angles. Make cross-tie gussets rectangular to overlap the two board ends.
- 9). Fasten gussets with four galvanized 1 1/4-inch screws, driven with a screw gun, into each gusset side.Turn the truss over and add a second set of gussets on the other side, being careful not to have screws collide. Set completed trusses aside until all are built.
- 10
Mark the wall caps for truss locations. Measure 1 1/2 inches in from the back-end wall and draw a line with a speed square and marker to mark the first truss location. Measure 23 1/4 inches in from the end wall and mark the outside line of the second truss; mark the inside 1 1/2 inches away. Measure 24 inches and mark another truss with 1 1/2-inch lines to the other end of the roof. Mark both wall caps identically. - 11
Raise the first truss at the back end of the shed. Lift it to the roof upside down, set it upright and secure it with three nails into each wall cap, toenailed, using 16d framing nails driven diagonally with a hammer. Put two nails on one side of the truss chord, one on the other. Install all trusses the same way. - 12
Add oriented strand board (OSB) decking, nailed to the trusses with galvanized nails, on both sides of the roof. Overlap the OSB at the peak, so a panel on one side goes over the end of the panel on the other side. Cut 4-by-8-foot panels with a circular saw as needed to fit the roof.
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