Steven L. Smith, Bellingham, WA Home Inspector (King of the House)

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Bellingham WA Home Inspector (King of the House) Multi-layer Roofs

At an older home, it is quite common to find multi-layer roofs, composition material over old comp or even over wood shingles (a real no no).  Despite the popularity of shingling over a worn out roofing surface, the practice is marginal at best. In the photo below, the rust colored shingles are the old roof below.

bellingham home inspector king of the house, roof problems

The psychology of the consumer is such that clients tell me they plan to put yet another layer over a roof that already has two layers. And somewhere in folklore, they have been told that it is okay to have three layers.

There are many problems with the theory. For one, if you have ever carried roofing materials up a ladder, you know that it is heavy. You start adding too many layers of the stuff and you are putting way more weight on the roof structure than it was designed to carry. 

bellingham wa home inspector king of the house, roof problems

Now that is one thick roof I am kneeling on. I wonder how much it weighs.  Other problems include the shingles not sealing well, so they tend to blow off in wind in blustery Bellingham and Whatcom County; the shingles not lasting as long as the warranty would indicate they should. A multi-layer roof will have maybe 80 percent of the estimated design life. The extra thickness often puts the surface of the roof in direct contact with siding or trim at dormers and that promotes rot. Speaking aesthetics, such roofs look funny, all wavy and unattractive. That is part of the reason the shingles blow off -- wind can get under them.

bellingham wa home inspector king of the house, roof problems

It is my advice that, when the roof requires replacement, the old roof should be torn off and a new roof, including felts and flashings in most cases, should be installed.

Steven L. Smith

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Comment balloon 5 commentsSteven L. Smith • October 25 2011 10:16AM

Comments

If you spend any time on this subject, you conclude the point of your post...The weight issue alone brings it home and that first wind will do the rest...good post with a point

Posted by Richie Alan Naggar, agent & author (people first...then business Ran Right Realty ) about 8 years ago

Around where I live we get a lot of snow. That roof would likely begin to fail here.

Posted by James Quarello, Connecticut Home Inspector (JRV Home Inspection Services, LLC) about 8 years ago

Steven, I have been told that a layer of shingles will have a reduced lifespan if it is installed over another layer of shingles.

Posted by Chris Smith, South Simcoe, Caledon, King, Orangeville Real Esta (Re/Max Chay Realty Inc., Brokerage) about 8 years ago

Agreed.  Wind vulnerable, snow weight vulnerable - bad practice vulnerable.

But can't squirrels burrow in there and have a nice dry home?

Posted by Jay Markanich, Home Inspector - servicing all Northern Virginia (Jay Markanich Real Estate Inspections, LLC) about 8 years ago

Steve,

I can hear the roof creak as you kneel on it. I wish they would outlaw that practice. I bet the flashing were all in great shape also ; )

Posted by Donald Hester, NCW Home Inspections, LLC (NCW Home Inspections, LLC) about 8 years ago

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