You will need to know how to build roof rafters when putting up a permanent structure on your property. The carpentry is very dependent on accurately measuring the roof pitch and span. These dimensions determine what figures to follow on a framing square when cutting the rafters.
Locate a roofing calculator tool online to perform the calculations necessary for determining rafter length. You may also choose to purchase the specialty calculator from a building supply store.
- Roofing calculator
- Framing square
- Square gauges
- Tape measure
- Circular saw
How to Build Roof Rafters Steps
- Measure width of the building from exterior wall edges to determine roof span.
- Subtract width of the ridge beam from roof span.
- Divide the adjusted figure by 2 to establish measurement for the building run.
- Enter this figure as the “run” in the roofing calculator.
- Calculate the roof pitch.
- It is expressed X/12 and may be included in your building plans.
- For example, a roof pitch of 7/12 rises 7 inches per every 12 inches of height.
- Enter this figure in the calculator for pitch.
- Have the calculator figure the “diagonal” measurement for the roof rafter.
- Adjust stair gauges on framing square to the numbers for the roof pitch.
- In this example, put a stair gauge at the 7 on the short tongue of the square.
- Place the other gauge at the 12 on the longer body of the square.
- Set framing square on the board with the 7 mark near the end.
- Rest the portion of the framing square with the 12 farther down the board.
- Mark a line from the 7 down the outer edge of the square.
- Saw the line to create your plumb cut for the rafter’s top.
- Measure along the top of the rafter board and mark the point where you reach the “diagonal” length.
- Position the 7 on the framing square at this mark and draw a line down the edge.
- Measure width of the wall.
- Subtract that figure from 12.
- Flip square around and place the long side of the square across the line on the number that represents 12 minus wall width.
- Make a second line that intersects with first line.
- Shift the square down the board for the number of inches you want the overhang to be.
- Mark that line.
- Saw out the notch where the rafter meets the wall.
- Cut the rafter’s end.
- Use this board as a template to cut other rafters.