How to Build a Sloping Roof

Cutting Rafters and Blocking

• 1

  Position portable scaffolds or A-frame ladders at each end of the slab or floor inside the building. Ask an assistant to hold the end of a measuring tape at the outside of the tall wall. Pull the tape the length of the building and note the rafter span at the outside of the short wall. Add additional space for overhangs at each wall, such as 12 or 24 inches, to establish the overall length of the rafters.

• 2

  Position a scaffold or ladder inside the building at one end of the tall wall. Hook the end of the tape over the outside end of the wall and begin marking 16-inch layout marks on the top of the wall with a carpenter’s pencil. Reposition the scaffold or ladder as you go and continue the 16-inch layout. Layout the opposite wall, starting from the same end as the first. Count the number of marks on one wall to establish the number of rafters.

• 3

  Stack several lengths of 2-inch thick Douglass fir lumber flat atop two sawhorses. Even the sides and ends of the pieces. Hook the end of the tape at one end of the stack and mark for the 12- or 24-inch overhang on the edge of the top piece. Reposition the end of the tape at the overhang mark and make a second mark that equals the span of the rafters from wall to wall. Make another mark for the other overhang at the end of the piece.

• 4

  Mark the edges of the stacked pieces at each overhang mark with a framing square. Set the depth of a circular saw blade at 2 inches. Put on safety glasses and cut the rafter to length with the saw. Lift the first rafter off the stack and notice the saw-blade mark that was made in the face of the piece below when you cut the first rafter. These are guide marks that transfer to each piece below as you cut each rafter to length.

• 5

  Repeat the previous step as you mark and cut the total number of rafters based on the count of the layout marks. Stand each rafter on end at 16-inch intervals inside the building against the tall wall as you go.

• 6

  Organize another stack of similar-size Douglass fir atop the sawhorses. Start at one end and mark the top piece at 14 3/8-inch intervals for rafter blocking. Square the marks with the framing square as you go. Cut twice the number of blocks as there are rafters, which provides blocks at each end of a rafter. Stage equal numbers of the blocks inside the building at each end of the rafter run.

Roof Framing

• 7

  Position scaffolds or A-frame ladders inside the building at the start of a rafter run against an outside wall. Ask an assistant to guide the upper end of the first standing rafter onto the top of the tall wall as you lift the lower end of the rafter onto the top of the short wall.

• 8

  Stand the rafter on edge and flush the outer edge with the outer face of the wall. Align the overhang marks at each end with outside edges of the tall and short walls. Toenail each end of the rafter to the top of each wall with two 16-penny framing nails and a framing hammer.

• 9

  Stand a rafter block on edge atop each wall and with one end against the first rafter. Flush the outer face of each block with the outer faces of the tall and short walls respectively. Toenail the blocks to the top of the walls with one 16-penny nail in the outer end of each block.

• 10

  Reach over the top of the rafter and drive three 16-penny nails, evenly spaced, through the face of the rafter and into the end of the block. Position the second rafter against the outer end of the block. Align the overhang marks and toenail it at each wall. Continue to install blocks and rafters progressively until all rafters are nailed in place. If necessary, measure and cut filler blocks that fit between the last two rafters at each wall.

Sheathing

• 11

  Position scaffolds or A-frame ladders at the outside of the short wall at one end. Fill your tool belt pouch with 8-penny framing nails.

• 12

  Ask the assistant to help load the first sheet of 1/2-inch CDX plywood sheathing onto the rafters. Even the lower, longest edge of the sheet with the ends of the rafter tails at the overhang. Even the end of the sheet with the outer edge of the first rafter. Secure the sheet in place with several nails at each rafter.

• 13

  Reposition the scaffolds or ladders and install the next sheet of 1/2-inch sheathing by butting the end against the end of the first sheet. Measure and mark the final sheet in the first course with a chalk line. Cut the filler piece with the saw and nail the piece in place.

• 14

  Stand an extension ladder at the lower end of the roof. Continue to load sheets of plywood onto the roof and nail each in place as you complete each course of sheathing. Mark and cut the filler pieces at each end with the chalk line and saw. If the upper edge of the final course extends beyond the rafter tails at the overhang, chalk a line from end to end and cut the excess at the line of the overhang. Otherwise, mark and cut filler pieces for the final course and nail these into place.

• 15

  Use the heads of the initial 8-penny nails as references and chalk lines on the sheathing that coincide with each rafter from end to end. Follow the lines as you nail the sheathing at 12-inch intervals at each rafter.