Installing standard asphalt shingles on a 2:12 pitch roof—meaning the roof rises two inches for every twelve inches of horizontal run—is generally not recommended and violates standard manufacturer application specifications unless exceptional waterproofing measures are implemented. Because a 2:12 slope is extremely low, water flows off very slowly, creating a severe risk that wind-driven rain will back up under the shingle laps and cause major interior leaks. If shingles must be used on a 2:12 pitch, manufacturers require a complete underlayment of heavy-duty ice and water shield membrane across the entire deck surface.
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