Commercial Building Inspector B2Roof Ceiling ConstructionMedium
A client is planning to install a new roof covering on an existing commercial building. The existing roof deck is structural concrete. The new roof covering will be a built-up roof (BUR) system. According to IBC Section 1507.4, what is the minimum slope required for a built-up roof (BUR) system, not including crickets or saddles?
- A1 unit vertical in 12 units horizontal (1:12)
- B1/2 unit vertical in 12 units horizontal (1/2:12)
- C1/4 unit vertical in 12 units horizontal (1/4:12)
- D1/8 unit vertical in 12 units horizontal (1/8:12)
Show answer & explanationAnswer & explanation
Correct answer: C. 1/4 unit vertical in 12 units horizontal (1/4:12)
IBC Section 1507.4.1 for Built-Up Roofs states that BUR roof systems shall have a design slope of not less than one-fourth unit vertical in 12 units horizontal (2 percent slope) for drainage, not including crickets or saddles.
Why the other options are wrong
- A. 1:12 is a significant slope, often used for metal roofs or shingle applications, not the minimum for BUR.
- B. 1/2:12 is a common slope for better drainage but is not the minimum required.
- D. 1/8:12 slope is generally too flat for BUR systems and can lead to ponding.
Built-Up Roof Minimum Slope
The lowest allowable incline for a built-up roof system, mandated by code, to ensure proper drainage and prevent water ponding.
- Specified in IBC Section 1507.4.1.
- Critical for the longevity and performance of low-slope roof systems.
- Prevents excessive water loads and membrane deterioration.
Memory trick: Roof slopes drain water like slides, BUR needs a quarter-inch drop.