You don’t need a 12-in-12 jig for the common and jack rafters because both the plumb and level cuts are 45º. Use a large triangular square to lay out these cuts.
J I G S & F I X T U R E S
Make a 12-in-16.97 jig for the valley rafters using the techniques described in “Building a Gable Roof” on p. 105.
Write the base-1 proportions (p. 503), the pitch in degrees (p. 505), and the backing angle (p. 502) on the jig.
Use a standard large square to lay out the common rafters.
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STEP 1 Lay out and install the ridges and the common rafters
The entire ridge for the main section can be installed at this point. The ridge for the wing is lower and must be attached to the main roof. In this framing plan, the lower ridge and the valleys are carried by a header, which is supported on each side by trimmers. The plan specifi es double 2×8s for the trimmers and a double 2×12 for the header. Steel hangers are specifi ed for carrying the header.
To prevent overloading one side of the upper ridge, leave the common rafters off until opposing rafters are installed.
Upper ridge
• UPPER RIDGE ON MAIN HOUSE
Using the techniques described in “Building a Gable Roof” on p. 105, lay out, cut, and install the ridges and common rafters.
Lower ridge Main roof common rafters Lower header Top plate
1
Lay out the position of the valleys on the top plates. Locate the trimmers just outside the valleys as shown.Trimmers
Valleys
2
After laying out the bird’s mouth of the trimmers, cut the ends at a 45º angle. This cut allows the valleys to run past the trimmers.Installed trimmers
Valley ends cut at 45º
Common and jack rafter tails are left long; they will be cut in place.
• LOWER RIDGE ON WING
The plan specifi es double 2×8s for the trimmers and a double 2×12 to carry the header. Steel hangers are specifi ed for carrying the lower header.
1
Set the header at the same height as the lower ridge with the bottom even with the underside of the trimmer.2
Rip the tops of the lower header at a 45º angle to con- form to the pitch of the roof.3
Add pieces ripped at a 45º angle to the underside. This brings the underside in plane with the common rafters.4
Extend the lower ridge to the header. Use a string or a straightedge to keep it in line with the rest of the ridge.STEP 1 Lay out and install the ridges and the common rafters (continued)
Double 2×8 trimmers
Steel hanger
STEP 2 Prep the valley material
1
Using the 12-in-16.97 jig, mark a plumb cut line on the 2×12 valley material.2
Measure the length of the plumb cut on acommon rafter (10¼ in.), and transfer to the
plumb line on the valley rafters.
3
Draw a perpendicular line through the mark on the valley material.4
Measure the distance from the edge to the mark (83⁄8 in.).5
Find the backingangle for a 12-in-12 roof, and rip a 30º bevel along the top edge.
6
Mark a line 83⁄8 in.from the top edge and rip a parallel bevel.
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STEP 3 Lay out and cut the plumb cuts and the bird’s mouth of the valleys
1
The key dimension for fi nding the base of the valley measuring triangle is the base of the common rafter measuring triangle. Multiply that dimension, 91.75 in., by √2 to determine the base of the measuring triangle for the valley: √2 × 91.75 = 129.75.2
Find the hypotenuse of the base-1 triangle for a 12-in-16.97. (It should be on your jig.) Multiply that number, 1.225, by 129.75 to determine the hypotenuse of the measuring triangle for the valley: 1.225 × 129.75 = 158.95 (15815⁄16 in.).3
Lay out the plumb cut at the top of the valley, set your saw to a 45º bevel, and cut along the plumb cut line.4
From the short point of the plumb cut, measure and mark 15815⁄16 in. along the bottom.5
From that point, use the jig to lay outthe bird’s mouth. Measure the layout line on the top of the wall to determine the correct length (about 6 in.) to make the
level line of the bird’s mouth.
6
Cut the bird’s mouth with the saw set to 0º.STEP 4 Lay out and cut the tails of the valleys
Because the rafter tails converge at the valley, it’s diffi cult to cut the ends of the valleys in place. To lay out and cut the valley rafters prior to their installa- tion, follow these steps.
1
Find the length of the base of the measuring triangle for the rafter tail. The rough eave is specifi ed at 10 in. from the outside face of the wall including a 1½-in. subfascia.2
The valley plumb cut is 8½ in. from the outside face of the wall.3
The walls are 4 in. thick so the plumb cuts need to be 12.5 in. from the inside face of the wall.4
The valley rafter runs at a 45º angle to the wall. The distance from the inside of the wall to the end of the rafter tail is √2 × 12.5 = 17.68.5
Multiply 17.68 × 1.225 to fi nd the hypotenuse of the measuring triangle for the rafter tail = 21.66 (215⁄8 in.).6
Use the jig to mark a plumb line 21.66 (215⁄8 in.)from the level line of the bird’s mouth.
7
Cut a 45º bevel along the plumb line.8
Use the jig to lay out the level line for the tail at the desired location. Set the saw to 0º and cut along the line.STEP 5 Install the valley rafters
5
The bevels at the lower end of the valley should run parallel with the walls and form a right angle.STEP 6 Lay out the common rafters in the area above the header
1
Install the fi rst board of the built-up valley.2
Install the second board back-to-back, then nail the two parts together.3
The bevels along the top and bottom edges of the built-up valley should form parallel Vs (with the points down) in cross section.4
The bevels at the upper end of the valleys should fi t into the rightangle formed by the header and the ridge.
1
On the upper ridge, fi nd the center of the space between the two trimmers.Header Lower
ridge
2
Lay out half of the upper ridge in a continuation of the 16-in. o.c. pattern of the common rafters to the left of the trimmer. Stop at the center mark.3
Butt a story stick against the left trimmer and record the layout. Reverse the story stick, butt it against the right trimmer, and transfer the mirror-image layout.4
Use the story stick to transfer an identical layout to the header.5
Use the story stick to mark a mirror-image layout along the lower ridge.Lower ridge Header
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STEP 7 Calculate the measuring lengths of the jack rafters
STEP 8 Lay out, cut, and install the jack rafters
Install the Remaining Common Rafters
Fill in the common rafters in the area above the header and on the other side of the upper ridge.
1
At the upper end of the valleys, measure the distances from the edge of the valleys to the far side of each rafter location. You can do this along the header or along the ridge; they should be identical. In this example, those distances are:4.75 20.75 36.75 52.75 68.75 84.75