The easiest way to frame a gable shed roof is with prefabricated trusses, ordered from a lumber yard or building supply store. But you also can frame a gable roof the old-fashioned way, using a ridge board and supporting rafters. This requires determining the length and pitch of the roof so the rafters can be cut diagonally at the proper angle to fit both the wall frame and the ridge board. Either roof option will require at least one person to help you.
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Things you need
- Tape measure
- Framing square
- Framing lumber (2-by-6)
- Framing nails
- Circular saw
- Roof trusses
- Eye protection
- Work gloves
- Roof sheathing
- Roof shingles
- Roof paper
- Roofing nails
- Metal roof flashing
Determine the width, length and pitch for your shed roof. This will dictate how many trusses or rafters you will need, how long your ridge board will be and the basic slope of your roof. You can make a very steep pitch or a shallow one -- for instance, a 5-pitch roof will slope at 22.5 degrees, a 10-pitch at 40 degrees. You need these calculations whether you're ordering prefabricated trusses or installing rafters. Trusses or rafters generally are spaced 24 inches apart and will be covered with some type of decking or roofing.
Calculate your rafter specifications, using a framing square and tape measure. Measure the span -- the width of the building -- and the rafter run -- the span divided by two. For a 12-foot wide shed, that would be a run of 6 feet. Determine the pitch, for instance 6/12, a rise of 6 inches for every 12 inches of run. Put your framing square at end of a rafter with the tongue (skinny part) on 6 inches and the body (fat part) on 12 inches, then draw a line along the square to mark the diagonal cut to fit the rafter against the ridge board. Repeat this down the rafter 12 times to mark the side wall cut. Then go back to the ridge cut and take off half the width of the ridge board -- for a 2-by-6, that would be 3/4-inch. Then cut all rafters the same.
Install your ridge board by nailing it, at the appropriate height, to two upright boards attached to the end headers (beams) at their centre points. Then nail your rafters to the ridge board and shed wall headers. You can buy metal hangers at a building supply store that make mounting the uprights, ridge board and rafters easier and more secure. Space the rafters at 24-inch intervals; you can adjust the spacing for the end rafters.
To install prefabricated roof trusses, mark their locations on the shed cap plate on both side wall headers. These should be 24 inches apart, although the end trusses should be flush with the exterior walls of the shed. The two end trusses will have more vertical framing to better support the gable ends. Nail those in place first. Nail temporary 2-by-4 supports from the truss to the ground to make it plumb. Raise trusses by laying them upside down over the roof, then lifting them into place vertically. As you place each truss, nail it to a top brace to keep the arrangement firm, evenly spaced and plumb.
Finish your roof with sheathing and shingles or roofing material. This will be basically the same, whether you installed rafters or roof trusses. For shingles, cover the roof on both sides with oriented strand board (OSB) sheathing, then attach roofing paper with nails and install shingles over that with nails, including ridge caps. For a corrugated metal roof, nail panels to rafters or trusses with corrugated grooves going down the wall. Overlap panels by one valley and finish with a metal roof cap. Put a metal drip edge under the sides of either style roofing.
Tips and warnings
- Raising trusses will require at least two and possibly four people.
- Nailing rafters to a ridge board will require at least two people working on ladders.
- You can cut the metal flashing to fit with tin snips or metal saw, but use caution -- the edges are sharp and will cut fingers and hands.
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