Using A Speed Square To Determine Roof Pitch

Made from plastic aluminum or steel this multi measuring tool combines a protractor a try square a ruler a.

Using a speed square to determine roof pitch.

A speed square and level can be used to easily find the pitch of a roof. Photo 2 shows how to use the speed square to mark a 33 1 2 degree angle the same as you would need on a rafter tail for a roof with an 8 12 pitch. What is a speed square. The speed square also called a rafter angle or triangle square is an extremely versatile tool originally intended to help carpenters quickly and accurately mark roof rafters it is a triangle shaped measuring tool that s invaluable for the diyer s tool box.

Swing the square until you read the desired angle on the board s edge and make your mark. Constructing a new shed roof at the desired pitch is as easy as knowing how to use a speed square. To calculate the required rafter length multiply the total run length half the building width plus the width that the roof is to overhang the house wall by this number 13 42. You can use the speed square to mark an angle such as when cutting a rafter tail by holding the pivot point against the board.

Directly below the 6 inch mark on the framing square read the required rafter length 13 42 per foot of run for a 6 inch rise 6 in 12 roof. Use a level and a pencil to make a plumb vertical line on one face of an existing rafter. Therefore if your roof rises 4 inches over the course of 12 inches of horizontal run then your roof pitch is 4 12. As stated in the video speed squares have useful markings on them from 0 to 12.

A roof slope of 4 12 is a 1 6 pitch a 6 12 slope is a 1 4 pitch an 8 12 slope is a 1 3 pitch and so on. Set the level on the edge of the speed square as shown below then place the heel of the speed square on a rafter or gable edge of the roof. While it is possible to estimate the amount of necessary materials using only the total roof area measurement as can be seen from the table depending how large the pitch of the roof the actual area of the roof can differ by up to 2 236 from the measured total area at a pitch of 24 12. 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.