How To Find The Angle Of A Roof With A Speed Square

Line up the pivot point on the bottom edge of the rafter.

How to find the angle of a roof with a speed square.

Because the speed square is a 90 degree angle each line on the diagonal represents one degree for a total of 90. Holding the level and speed square level locate the measurement on the speed square where it meets the bottom edge of the rafter to find the angle of the roof in degrees. Draw a line down the pivot point edge of the speed square on the exact same side that the 90 degree line was drawn. Place the pivot point on the square against the bottom of the rafter and align the 90 degree angle side of the square with the pencil mark.

The hash marks with corresponding numbers between 1 and 30 refer to the roof s rise angle. Step 2 find an angle. This is called the plumb line. The pivot is a point at one end of the lip about which you can rotate the speed square to find angles.

Hold the pivot point against the board and move the square until your desired angle lines up with the edge of the board. Align the lip of the rafter angle square along the plumb line. Step 3 note the number on the common scale parallel with the 45 degree angle of the square. As an example pivot the speed square until the numeral 30 aligns with the opposite edge of the piece of material.

Read the pitch on the side of the rafter square. Place the pivot point against the shingles. If not the 0 degree mark should be at the opposite. Then place a torpedo level on the fat base of the rafter square and adjust the square until the level is level.

Follow the bottom edge of the rafter to where it meets the common pitch reading. It s often marked right on the tool. Now that the square has been lined up on the 30 degree mark however the angle drawn will be a 30 degree angle. Use a spirit level to mark a straight vertical line across the rafter.