Understanding your calculation
Method, example and limitations
How the calculation works
A sloped roof has more surface area than its horizontal footprint. For a simple roof plane, slope adjustment uses the relationship between rise, run and sloping length.
Example to check
A plane with a 3-by-4 rise/run triangle has slope length 5, so its surface area is 1.25 times its corresponding horizontal area.
Before using the result
Hips, valleys, dormers, overhangs and material overlap add complexity. Confirm quantities and structural details with a qualified roofer.