Low-slope roof

OSHA's definition turns on a single ratio. Section 1926.500(b) of its construction standard calls a roof low-slope when its slope is 4 in 12 or less, vertical to horizontal, and steep when the slope is greater than that. How those ratios are written, and how they differ from the roofing manuals' units, is set out under roof pitch.

The definition matters because 29 CFR 1926.501 writes a separate fall protection paragraph for each side of that line. On a low-slope roof, section 1926.501(b)(10) keeps the three systems of the general rule, guardrail, safety net and personal fall arrest, and adds combinations built around a warning line: a warning line with a guardrail, with a safety net or with a personal fall arrest system, or a “warning line system and safety monitoring system.” The duty itself, and what each system is, belongs to the entry on fall protection.

Those low-slope options are written for employees “engaged in roofing activities,” and the same section 1926.500(b) defines roofing work as the hoisting, storage, application and removal of roofing materials and equipment. The definition names no cleaning. Whether a cleaning job falls under these construction rules or under a different part of OSHA's rules is a question this glossary does not settle; it belongs with OSHA or with counsel, and the 6-foot rule is cited here as the benchmark the trade works to.

The Asphalt Roofing Manufacturers Association uses the same words for a different job. Its Residential Asphalt Roofing Manual says that, in general, most asphalt shingles may be installed on slopes from 4 inches per foot to 21 inches per foot, 4:12 to 21:12, with standard application methods, and that most may be used on slopes from 2:12 to less than 4:12 if “special low slope application procedures are followed.”

Set the two lines next to each other and they almost meet. OSHA's low-slope definition includes a roof at exactly 4 in 12. ARMA's low slope range stops just short of 4:12, and a shingle roof at 4:12 is back in the standard application range. So a 4:12 shingle roof is low-slope in OSHA's sense and standard in ARMA's. Neither body is correcting the other: OSHA is sorting roofs for fall protection, and ARMA is telling installers when most shingles need special procedures.

Neither line says anything about cleaning. Where a low-slope roof carries a membrane, that membrane's maker is the one to ask what it will take. A pressure figure one maker publishes stays with that maker's own product, and a published pressure number does not carry over from one roofing material to another.