DIY Saltbox Roof Trusses

Make saltbox roof trusses like gable trusses, except for the shorter slope. Get the pitch, or angle of slope; 5/12, which rises 5 inches per foot of rafter run, is a common pitch, but the short side may have a different pitch. Determine the rafter run, the distance each rafter must support; on a saltbox, this requires two measurements -- one on the long slope and one on the short, the distance from the peak to the wall on each side.

Figure the plumb or top cuts for both sides with a framing square. Put the point or heel of the square at the bottom of a 2-by-4-inch rafter board. Align the pitch mark, 5 in this example, on the thin tongue of the square and the 12-inch mark on the wide blade at the top of the board. Mark that angle at the end of the long rafter chord. Mark a similar cut angle on a short chord for the other side of the roof. Use the same method but with the pitch of that slope if it is different from the long slope; some saltbox roofs have steeper short sides.

Use the "length of common rafter" table on the square's blade to figure the length of rafter needed. Look under the pitch mark for that difference; for a 5/12, it is 13, meaning each rafter must be 13 inches long for every foot of run. Multiply that by the rafter run; on a 12-foot wide building, the long run might be 9 feet, the short one 3 feet. Use a tape measure to mark those distances -- in this example, 117 inches for the long run, 27 inches for the short run, although this can vary if the short pitch is not 5/12.

Decide whether trusses will have a bottom chord that rests on the wall caps with rafters that overhang or whether bottom chord and rafters will join at that bearing point. Measure a 2-by-4 to fit between the wall caps. Lay out a pair of rafters with plumb cuts together and mark the connection angles on the bottom chord. These will vary with the pitches of the two roof sides and the selected bearing point. Cut a bottom chord to fit.

Measure from the bottom of the peak to the bottom chord and cut a 2-by-4 for a vertical brace under the peak; that will suffice for most sheds and small outbuildings. Make gussets of 1/2-inch plywood to overlap the joints, at the peak and each rafter end. Cut the top gusset with angled sides to conform to the rafter slopes and a horizontal bottom overlapping rafters. Secure gussets, on both sides of the truss, with 1 1/4-inch ring shank nails driven with a hammer.

Add diagonal braces for wider trusses. Angle one from the bottom of the vertical post to the center of the short rafter. Angle one on the long rafter from the bottom of the post to about a third of a way down the rafter, then add a diagonal from the top of that brace to the bottom chord and another from the bottom of that brace to the rafter. Those braces should form three triangles between the bottom chord and the rafter. Secure those joints with gussets.