How to Build Rafters for a 12-by-16 Gable End Shed
Making a traditional shingle roof for a 12-by-16-foot shed requires building rafters or trusses. You can buy prefabricated trusses or make them yourself or just frame the roof with standard rafters. Trusses are simply rafters that are nailed together with braces and installed as a unit, while rafters are installed as individual components. All you need is the pitch or slope of the roof, the building dimensions and a framing square -- plus enough carpentry skill to cut and nail boards. Does this Spark an idea?
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Things You'll Need
- 2-by-4-inch rafter boards
- Framing square
- Pencil
- Tape measure
- Circular saw
- Hammer
- Framing nails
- Level
Instructions
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Use the pitch and run of the rafter to determine the first angle or cut. A typical shed roof will be 4/12 pitch, sloping 4 inches per foot from peak to wall. The run is half the width, 6 feet for a 12-foot shed. Start with an 8-foot 2-by-4-inch board to make a pattern rafter. You will need 16 rafters for a 16-foot long shed, spaced 24 inches apart with one rafter on each side of the peak.
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Lay the board with the 4-inch face up and put the framing square at one end with the thin side, tongue, to the right. Set the point, heel, of the square at the bottom of the board. Align 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 on the tongue called the top or plumb cut. Mark that with a pencil.
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3
Figure the length of the rafter with the "length of common rafter per foot of run" line on a table embossed on the blade of the square. Look under the 4; it will show 12.65, meaning a rafter must be that distance (about 12 1/2 inches) for every foot of run or 75 inches for a 6-foot run. Measure with a tape measure that length from the bottom of the plumb cut down the board and mark it. Measure another 3 1/2 inches, mark that spot, then measure 1 inch into the board at that point. Draw a triangle from that mark to 75-inch mark. That's a notch called a birdsmouth which will fit over the top of the wall.
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4
Add some overhang to extend beyond the wall, at least a foot. That makes the total rafter length 87 inches or 7 1/4 feet. Mark that spot and make another angle, reverse of the top cut, by placing the heel of the square at the top of the board. Take another 3/4-inch off the plumb cut and mark that angle the same as the original; this will provide space for a ridge board at the peak to tie the rafters together.
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Mark and cut all rafters to that pattern with a circular saw. Erect one pair of rafters at one end of the roof. Nail the birdsmouth to the wall cap on each side with a hammer and framing nails. Let the plumb cut ends just rest against each other. Go to the other end of the roof and raise and fasten another pair of rafters. Set a 16-foot 2-by-4 between the rafters on each end. Slide it into place from the bottom. Use a level to level it and make sure the rafters are vertically plumb, then nail the rafters and ridge board together.
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6
Raise and set the other six rafter pairs one at a time, one rafter on each side of the ridge board. Make sure each rafter pair is plumb and the ridge board stays level. Add cross or collar ties to each rafter pair to make a stronger roof; these are 2-by-4s cut on the ends to match the rafter angle and nailed between the rafters about a third of the way down from the peak.
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Tips & Warnings
Have help. Raising rafters will require at least two and preferably three or four workers.
