How To Look At A House
McGarry and Madsen's home inspection blog for buyers of
site-built, mobile/manfuactured and modular homes
What causes a shingle roof to deteriorate faster and fail prematurely?
Tuesday, June 18, 2019
Premature deterioration of a shingle roof can be caused by the site, manufacturing defects, weather, improper installation, or inadequate maintenance. But often it results from a combination of them:
• Manufacturing defects - Shingles that crack easily, don’t develop adequate tab adhesion, or lose surface rock granules rapidly probably have a manufacturing defect. Unless the defects are especially egregious, it can be hard to prove to a manufacturer’s representative. They tend to fall back on “improper installation” as a response to complaints. A recent exception was the replacement of the shingle roofs in an entire neighborhood in The Villages, Florida, by the manufacturer due verified defects that reduced tab adhesion.
• Improper installation - Every asphalt shingle manufacturer has their own installation standards, and they also differ acording to which type and grade of shingle is being installed. What might be the correct nailing pattern for one manufacturer’s shingle, for example, sometimes is not right for another. Certain basic installation problems, like overdriving or underdriving nails will shorten the life of any roof, and often the shingles loosen and come off in strips like in the photo below.
• Thunderstorms and hurricanes - Even a storm that does not tear off shingles does damage. The high winds and driving rain loosen and wash away some of the granule covering of the shingle, which speeds up the exposure to sun’s deteriorating UV-rays.
• Intense sunlight and thermal cycling - These are two factors we have in abundance in Florida, especially on the south-facing slope of a roof. Bright sun and extremely hot summer days, then a cool-down each evening. Dark color shingles sometimes get too hot to touch with bare hands. The shingles are protected from UV-light damage by the cover granules but, as they wear away, combined with the daily cycle of expansion and contraction from temperature change, the sun takes its toll on a roof.
• Poorly ventilated attic - We have been in attics with the soffit vents covered over with insulation, like in the photo below, and no ridge vents that have reached over 140º F. This is a separate issue from heat cycling, and causes intense heat under the shingles. Attic ventilation is important.
• Severe cold and ice dams - Wish we could tell you more about this, because ice dams can creep under shingles and ruin both the roofing and sheathing below it, but it’s not something we see in Florida.
• Trees - Heavy shade from a dense tree canopy over the roof will encourage algae growth, and tree branches that brush over the roof surface in the wind can destroy an area of shingles in just a couple of years.
• Leaf debris on the roof, especially in valleys - The tannic acid seeping though of a pile of rotting leaves in the valley of a roof stains and attacks the shingles while slowing water drainage.
Shingle deterioration tends to accelerate in the final third of a roof’s lifespan, even under normal conditions. As granules fall away from the shingle surface, asphalt is exposed to the sun’s rays and gets progressively more brittle. Meanwhile, the adhesive tabs at the leading edge of each shingle start to loose their grab. When the wind gets under a shingle with a loose edge and pulls it up, the shingle is no longer pliable and snaps off—like in the photo at the top of the page.
There are several things you can do to make your roof last longer: keep tree branches away from the roof surface, remove any leaf debris that accumulates, check on your roof from the ground as you walk around it regularly, and have a professional roofer inspect the roof every two or three years and make any minor repairs needed.
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Here’s links to a collection of our other blog posts about SHINGLE ROOFS:
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