How to Find the Pitch of an Existing Roof
If you need to find the pitch of an existing roof all you need is a level and a tape measure. Working from the interior side of the roof you’ll need access to a roof rafter to measure the pitch. Place the level horizontally along the rafter until it contacts the roof sheathing, avoiding any protruding roof nails. Keeping contact with the sheathing, adjust the angle of the level until the bubble is centered in the vial and clamp it to the rafter. Next, hook the tape measure to the level where it meets the sheathing and extend it out to make a mark at 12 in. Roof pitch is expressed as rise over run, so 12 in. would be the run. Then, place your tape at the 12-in. mark and measure up to the roof deck to get the rise. The rise over run numbers give you the pitch.