What is the minimum slope for a roof with a coal-tar built-up roof?

What is the minimum slope for a roof with a coal-tar built-up roof?

• A. 1/8 unit vertical in 12 units horizontal
• B. 1/4 unit vertical in 12 units horizontal
• C. 2 units vertical in 12 units horizontal
• D. 4 units vertical in 12 units horizontal

Answer: (A)

The main idea is drainage: flat roofs must have enough slope so water can flow to drains and not pond. For coal-tar built-up roofs, the minimum slope specified is one-eighth inch of rise for each horizontal foot. In other words, a rise of 1/8 inch over 12 inches of run. This provides a reliable drainage path for the tar system without requiring a steeper pitch. Steeper slopes (like 1/4 inch per foot or more) are more than necessary for this material, and much steeper slopes (2 inches or 4 inches per foot) would be impractical for a flat roof. A slope of 1/8 inch per foot is the lowest acceptable that still ensures proper drainage for a coal-tar built-up roof.

The main idea is drainage: flat roofs must have enough slope so water can flow to drains and not pond. For coal-tar built-up roofs, the minimum slope specified is one-eighth inch of rise for each horizontal foot. In other words, a rise of 1/8 inch over 12 inches of run. This provides a reliable drainage path for the tar system without requiring a steeper pitch.

Steeper slopes (like 1/4 inch per foot or more) are more than necessary for this material, and much steeper slopes (2 inches or 4 inches per foot) would be impractical for a flat roof. A slope of 1/8 inch per foot is the lowest acceptable that still ensures proper drainage for a coal-tar built-up roof.