How To Look At A House
McGarry and Madsen's home inspection blog for buyers of
site-built, mobile/manufactured and modular homes
What causes bubble-like blisters in a built-up and gravel roof?
Saturday, June 16, 2018
When moisture seeps between the plies of a built-up and gravel roof, and then the sun comes out and heats up the surface, the water turns to vapor. Expansion of the trapped gas causes a raised pocket, known as a blister, to form. The blister will often loosen the gravel and some of it will slide away from the area, allowing more deterioration, and leakage.
An older blister like the one shown in the photo at the top of this page is not just visible. When you step on it, the blister makes a squishy sound from the trapped water inside.
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Here’s links to some of our other articles about “FLAT ROOFS (LOW SLOPE)":
• Why does it cost so much more to replace a steep roof than a low slope roof?
• Why are most house roofs slanted instead of flat?
• What is "ponding" on a flat roof?
• Why is there no attic access hatch in the house?
• What is the difference between roll roofing and modified bitumen?
• What is the purpose of the gravel on a flat tar roof?
• Can metal roofing be used on a low slope/pitch roof?
• What is the stuff you paint an old mobile home metal roof with to extend its life?
• Does a gravel roof need maintenance?
• What is the average lifespan of a built-up and gravel roof?
• What is the average lifespan of a modified bitumen roof?
• What is the average life expectancy of a TPO (Thermoplastic PolyOlefin) roof?
• What is the average life expectancy an EPDM roof?
• I'm buying a '50s modern house with a "gravel" roof. Is the roof going to be a problem?
• Is "ponding" (standing puddles of water) normal on flat roof?
• What is the average life expectancy of a built-up roof?
• What is the average life expectancy of an elastomeric roof coating?
• Can you coat a TPO roof to extend its life?
• What causes ponding (standing water) on a flat roof?
• What are the signs my flat roof needs to be replaced?
• What is the average life expectancy of a PVC roof?
Visit our ROOF AND ATTIC page for other related blog posts on this subject, or go to the INDEX for a complete listing of all our articles.
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