What Causes Rolled Roofing to Fail During Rain Events?

Rolled roofing materials, like modified bitumen or asphalt sheets, degrade over time from sun exposure and temperature swings. The material can become brittle, leading to cracks, or it can soften and blister. These blisters eventually rupture, creating holes.

Intense UV radiation and extreme temperature swings accelerate this aging. The asphalt can become brittle and crack, while sudden, heavy rainstorms exploit any new weakness. Regular visual checks for cracks or granule loss can help spot problems early.

• Ultraviolet radiation makes the asphalt brittle.
• Thermal expansion and contraction cause stress cracks.
• Loss of protective mineral surfacing granules exposes the base.
• Blistering from trapped moisture under the membrane.
• Shrinkage over time, pulling nails or opening seams.
• General weathering from wind, rain, and debris.

Rolled roofing is secured with nails or special fasteners along the edges and seams. If these are spaced too far apart or driven incorrectly, wind can get underneath the sheet. This wind uplift works the fasteners loose over time.

During a rainstorm, wind-driven rain is forced under any lifted edge. Once water is underneath, it can travel laterally far from the original entry point. This makes the source of a leak inside your home difficult to trace back to the actual roof failure.

• Fasteners spaced wider than manufacturer specifications.
• Nails driven too deep, damaging the roofing material.
• Nails not driven flush, creating a snag point for wind.
• Using the wrong type of fastener for the substrate.
• Fasteners corroding over time, losing holding power.
• Failure to properly seal fastener heads with roofing cement.