How to Measure a Rise on a Vertical Section of a Roof & Its Lower Edge

Attach a level to the bottom arm of the framing square with rubber bands or twine. The level can rest on the bottom arm or along the front side, whichever is more secure. The side edge of the level should contact the vertical side of the square to keep it out of the way of the roof. Note that depending on which side of the roof you're measuring, either arm could be the bottom arm, so decide which side you'll measure on before attaching the level.

Hold the framing square up against the side of the roof near the bottom. The roof is likely sticking out a little from the side of the building, so you won’t be able to steady it against a wall. If the edge is up fairly high, stand on a ladder. The ladder should be on the side of the building and not in front.

Place the outside corner of the bottom edge of the framing square against the bottom of the roof on the side of the building. Ensure the level shows the framing square's bottom arm is horizontal. Use a framing square that’s fairly large and that can measure more than 1 foot horizontally. If you use one that measures exactly a foot, you’ll have to balance the corner of the square very carefully against the edge of the roof. A longer framing square means more stability.

Push the framing square out past the roof’s edge until you have 12 inches measured between the bottom edge and the start of the vertical side of the framing square.

Read off the number on the vertical side where it meets the bottom of the roof. This is the vertical rise.