To measure pitch first position the hypotenuse of the square on the roof running.
How to build a 45 degree angle roof.
The square also comes with three leveling vials which make it easy to measure the pitch of existing structures.
Install the corbels next.
Set unit run place the other square gauge at the run unit measurement mark.
Screw the gauge in place.
This means if a roof rises 4 in the length of 12 your roof pitch would be 4 12 or 18 43 degrees.
You can make the 20 degree cut following the set angle flip the tool over and make the complementary 70 degree cut to create a perfect 90 degrees.
For each one place the top of the corbel flush with top of the door trim and the side against the side of the door trim and screw into place.
To determine material quantities you need to do some calculations.
Set cut angle for rafter place the framing square so the blade is horizontal on the rafter and the tongue is on the rafter and draw lines.
Screw the square gauge on the tongue at the marker for the slope pitch of the roof or the unit rise.
Before miter saws and even since professional carpenters used speed squares as a quick saw guide for cutting 45 and 90 degree angles.
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.
Accuracy is key here because miscalculations could lead to major overspending.
The steepest pitch for a roof is 12 12 which creates a 45 degree angle and where the roof vertically rises 12 inches for every 12 inches it goes horizontally.