Stucco: Invasive Testing vs IR Scanning

I've heard of home inspectors in Minnesota offering infrared scans on stucco homes as an attractive non-invasive alternative to standard invasive moisture testing.  Here at Structure Tech, we recently started offering infrared inspections, but stucco scans are something we will never offer.

Stucco Crack First, some info on stucco.  Stucco homes in Minnesota built since the late 80's or so have had a nasty history of catastrophic failures.  These stucco homes are more likely to have moisture instrusion problems than other types of homes, and the damage is usually far more serious. The City of Woodbury has an excellent position paper about Stucco in Residential Construction, which should be required reading for anyone buying a stucco home built during this time period.  In many cases, there are absolutely no visible signs of moisture instrusion.

Invasive Testing

My advice to anyone buying a newer stucco home in Minnesota is to have invasive moisture testing performed, which can be done from the interior or exterior (this blog isn't going to be a discussion of the two methods, although that will be a great future topic).  Exterior testing is done by drilling holes and  sticking metal probes in to the wall to measure the moisture content of the wood.  One such company that offers this service is Certified Moisture Testing, who we have recommended many times over the years.

Invasive Stucco Testing
These holes get covered over with matching caulk after the work is done, and there is virtually no evidence that any work was ever done.  Interior testing is done in a similar manner, where holes are made inside the house and the moisture content of the wood is tested.  As long as the person doing the testing is good at it, the results that come from invasive moisture testing on stucco homes are highly reliable.  

Infrared Scans on Stucco

IR Image of bad window Having a stucco home scanned with an infrared camera as an alternative to invasive moisture testing may sound like a great idea, as there are never any holes left in the walls with this testing method.  The problem is that infrared scans on stucco are unreliable.  Infrared cameras don't see inside walls; they only show differences in temperature.  

For example, the image at right is an infrared image of a window at a stucco home.  You can see a little green at the lower left corner of the window, which means this area is a little bit colder.  This was the worst area of moisture intrusion at the home, and an invasive moisture test found there was no wood to probe here; the wood had rotted away to nothing.  

If only an infrared scan had been performed, what would the recommendation have been?  Tear the wall open?  Have an invasive test performed?  This was the only thermal anomoly shown on the entire house, but an invasive moisture test found unacceptable moisture levels in about a dozen other areas throughout the house. 

Temperature differences may or may not equate to moisture intrusion.  Conversely, if there are no temperature differences in stucco, should one conclude that there is no moisture in the wall?  Absolutely not.  Infrared cameras are great at finding temperature differences, but not water. Infrared cameras can be used to give clues for places to perform invasive tests at best.

The bottom line is that infrared scans on stucco homes will give unreliable results and should not be considered an alternative to invasive moisture testing.  I'm a firm believer in invasive moisture testing on stucco homes, and I say this as someone with no financial interest in the matter.

Reuben Saltzman, Structure Tech Home Inspections - Email - Infrared Home Inspections

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Written By

Reuben is a second-generation home inspector with a passion for his work. He grew up remodeling homes and learning about carpentry since he was old enough to hold a hammer. Reuben grew up thinking he was going to be a school teacher because he enjoyed teaching others so much. In a sense, that’s a lot of what home inspections are about, so Reuben truly does what he loves. Sharlene has worked with Structure Tech since 2000 and Reuben has been contributing to her blog since 2008.

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