How To Look At A House

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site-built, mobile/manufactured and modular homes

Do flat roofs always leak?

Monday, October 4, 2021

Not true. But it may seem like that to a frustrated homeowner with an older flat (low-slope) roof. Here’s three reasons why:

1) Flat roofs leak more water when the roof begins to fail - A sloped roof only has to resist water briefly as it rolls over the surface and heads quickly downhill. Although roofs that are called flat all have a slight slope for drainage, low spots develop over time where water puddles until it evaporates. Because leaves tend to collect in the low spots and add acidity to the standing water, this hastens roof deterioration. And these are often the first places to leak, with the water continuing to drip through even a tiny opening until the puddle has drained. So flat roof leaks tend to be more dramatic.

2) Flat roofs typically don’t last as long as sloped roofs - Several common flat roof materials have a shorter average lifespan than their sloped roof counterparts. The 3-tab shingles at the left in the picture above have a 20-year average life, while the modified bitumen flat roof is rated at only 15-years—making it likely to fail first.

3) Installing a flat roof requires more skill and experience to do correctly than a sloped shingle roof - So a sloppy installation of a flat roof is more likely to leak. 

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Here’s links to some of our other articles about “FLAT ROOFS (LOW SLOPE)":

• How do I minimize roof penetrations?

What causes bubble-like blisters in a built-up and gravel roof?  

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 a TPO 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 an EPDM 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 a low slope 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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