What Does Low-Slope Roof Mean?
As the name suggest, a low-slope roof is a roof with a slope that has a low elevation. Low-slope roofs have a vertical rise to horizontal run ratio of 4:12. In other words, for every 12 inches of horizontal run, there are 4 inches of vertical rise.
Low-sloped roofs are sometime referred to as flat roofs. This is a misnomer, however, since all roofs that meet building codes must have a certain amount of slope in order to allow drainage and prevent rainwater or melted snow from pooling.
To prevent confusion, the Occupational Safety and Health Administration (OSHA) standardized the term "low-slope roof" to ensure that everyone choosing fall protection equipment while working on a roof will account for the presence of a slope.
Safeopedia Explains Low-Slope Roof
OSHA 1926.500(b) specifically defines a low-roof slope as "a roof having a slope less than or equal to 4 [inches] in 12 [inches] (vertical to horizontal)." A roof that exceeds those measurements is referred to instead as a steep roof.
Working on Low-Slope Roofs
Working on roofs comes with inherent risks, such as potential falls and weather hazards. The slope of a roof will have a considerable influence on the severity of the risks as well as the degree of protection required to mitigate them. A high pitched roof increases the risk of workers losing their footing, materials falling off the edge, and slipperiness as a result of rain or ice.
Anyone working on a low-slope roof with unprotected edges is required by OSHA 29 CFR 1926.501(b) (10) to have adequate fall protection in place, consisting of one of the following combinations:
- Guardrails, safety net, and a personal fall arrest system
- Warning line system and guardrails
- Warning line system and safety net
- Warning line system and personal fall arrest system
If the roof is equal to or narrower than 50 feet in width, OSHA allows the use of a safety monitoring system without a warning line system.
Risk Zones on Sloped Roofs
No matter the degree of slope, a sloped roof is divided into three zones based on the level of danger they pose to workers:
- Red zone (extremely-high danger) – The six feet closest to the leading edge of the roof. This is where most falls and accidents take place. Slips, trips, and falls in this zone can result in injuries with much higher severity since as workers are more likely to fall off the nearby edge. If using a guardrail system, the guardrails are to be installed in the red zone.
- Orange zone (very high danger) – Six to fifteen feet from the leading edge of the roof. While safer than the red zone, being within fifteen feet of the leading edge still poses a significant risk of falling or tools dropping over the edge.
- Green zone (high danger) – 15 feet or further from the leading edge. This is the area with the lowest risk for falls off the edge or dropped objects. However, it can sometimes present new hazards, such as skylights and uneven elevation (a tripping hazard).