Using A Speed Square To Determine Roof Pitch

What is a speed square.

Using a speed square to determine roof pitch.

Use a level and a pencil to make a plumb vertical line on one face of an existing rafter. How to measure roof pitch with a speed square. 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 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.

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. Therefore if your roof rises 4 inches over the course of 12 inches of horizontal run then your roof pitch is 4 12. Constructing a new shed roof at the desired pitch is as easy as knowing how to use a speed square. 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. 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. A speed square and level can be used to easily find the pitch of a roof. I hear read all too often this misuse and usually ignore it.

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. If a magazine such as finehomebuilding is going to put out an article to teach a topic it should use the proper words and definitions. Swing the square until you read the desired angle on the board s edge and make your mark. Made from plastic aluminum or steel this multi measuring tool combines a protractor a try square a ruler a.