Ask the Architect

Why aren't our roofs lasting?

Posted

Q. We’ve replaced our roof three times since we bought our house in 1988. Each time they told us it was a 30-year roof, but they haven’t lasted more than 10 years at the most. Before we go through all this again, we need to know, why do the roof shingles darken, curl and disintegrate? This shouldn’t keep happening!

A. Your roof is suffering from strangulation, right before your eyes. Sadly, the culprit is constantly there, committing this crime, but the accomplice is long gone. The culprit is heat buildup, which warps the roof structure and stretches shingles, which in turn makes them split, and the accomplice is the installer.

You see, heat from the attic and roof cavities below the shingles dries the shingles out, which causes the granular coating to loosen and run off in the rain, exposing the waterproofing and fiber substrate, which more quickly erodes and disintegrates, developing holes that allow rainwater to saturate and pucker the plywood or planking roof boards. Aside from delaminating the roof boards (called substrate), the seams of the boards open and water flows in or finds its way along the shafts of roofing nails. Roof nails maintain their general size over time while the wood loses moisture and shrinks, so there are spaces around the nails that permit water to flow around.

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