How is the slope of a roof expressed?

The slope of a roof is correctly expressed as a ratio of rise to run. This ratio indicates how much the roof rises vertically (the rise) for every horizontal foot (the run). It is a key aspect of roofing as it determines how water will drain off the roof and can influence material choices and structural integrity.

Using a ratio captures the relationship between vertical and horizontal measurements succinctly, making it easier to compare different roof designs. For example, a slope expressed as 4:12 means that for every 12 horizontal units, the roof rises 4 vertical units. This clear ratio helps contractors and builders ensure they meet necessary roofing codes and standards related to slope requirements.

Expressing roof slope in degrees, as a percentage, or in square feet does not adequately convey the essential rise-to-run relationship essential for determining a roof's functionality and aesthetic design. Each of these alternatives has its own metrics and use cases, but for the simplicity and clarity required in roofing work, the rise-to-run ratio remains the standard method.