How To Look At A House
McGarry and Madsen's home inspection blog for buyers of
site-built, mobile/manfuactured and modular homes
What is a termite shield?
Saturday, August 4, 2018
It is a piece of sheet metal—typically galvanized steel, copper or aluminum— that is installed between the stem wall or piers of a home’s foundation and the wood framing members sitting on top, to serve two purposes:
1) Deters termites from reaching the wood structure of the home - Subterranean termites require a moist environment to live, and they build mud tubes from the ground up into a home that are sealed tunnels which protect them from the dry outside air while they search for wood to consume. Because it is difficult for termites to to build their mud tube around the sharp edge of a shield, like the ones shown in the photos above and below, the metal strip slows down their march up into the house. It often forces them, at least for a while, to search for an alternate route upward. But eventually they can get around them.
2) Makes it easier to spot their mud tubes - Termites are very small creatures and can navigate through cracks as small as 1/32 of an inch to enter a home concealed from view. The metal strip creates a “no-mans-land” that they must cross in plain view to get to the wood structural members of the home. This makes it easier for an inspector to examine a crawl space to find evidence of termite activity.
Termite shields have been a standard construction detail for homes with elevated wood floors for many years. But they must be carefully installed with no gaps in the coverage of the top of the stem walls or piers in order to be effective. Also, any corrosion pinholes that may develop over time provide a concealed entry point. In the photo below, mortar that was dropped on the termite shield by masons working above it has eliminated the effectiveness of the sharp edge of the shield with a bridge of mortar lumps.
So termite shields are not a cure-all, and should be used in conjunction with ground treatments and/or bait traps as part of a termite protection plan. The photo below is an example of termites sending up exploratory mud tubes from the small crack in a different type of location: between a garage floor slab and a laundry platform at the back of the garage. This means that any opening, even a tiny one, can become an entry point.
Also, it is worth noting that shields protect a home from subterranean termites; but drywood termites do not need to enter a home from the ground and can get to the wood of a home during swarming season by flying into any opening to establish a colony. Luckily, they do not build their colonies as quickly or eat the wood in your home as aggressively as subterraneans.
Also, see our blog post How do termites infest a house and remain hidden while doing major damage?
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To learn more about termites, see these other blog posts:
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