How To Look At A House
McGarry and Madsen's home inspection blog for buyers of
site-built, mobile/manufactured and modular homes
Do manufactured/mobile homes have more foundation problems than site-built homes?
Thursday, April 28, 2022
Most manufactured homes are installed on a foundation consisting of piers of stacked concrete blocks on top of a plastic or concrete foundation pad. Protection against uplift forces and lateral stability is provided by tie-down anchors and lateral arm systems secured to the home’s steel beam undercarriage. The entire foundation system is above-ground, except for steel anchor rods into the soil at the base of the anchor straps and some foundation pads. This means that a mobile home foundation is more susceptible to problems caused by surface soil movement than a site-built home foundation, which is typically totally underground and runs continuously around the perimeter of the home.
So surface soil movement is the scourge of manufactured home foundations. This is why HUD requires a home to be installed on a raised soil pad that slopes a minimum of 1/2-inch per foot away from the home for 10-feet on all sides. See our article What are the HUD requirements for site drainage when installing a mobile/manufactured home? for more on this.
Unfortunately, many older manufactured homes were not installed to that site drainage standard, and rain water runs across under the home or pools in a low spot. Also, many have no gutter and downspout system to move roof water away from the home. But the good news is that a manufactured home foundation is easily accessible to check and repair as necessary because it is totally above ground in the crawl space. And a foundation tune-up is part of the occasional re-leveling process for manufactured homes as they age.
Also see How can I tell if a mobile/manufactured home will pass a foundation certification inspection? and What are the most common defects in mobile/manufactured home foundation piers? and What are the tie-down requirements for a mobile home?
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Field Guide for Home Inspectors, a quick reference for finding the age of 154 brands of HVAC systems, water heaters, and electrical panels, plus 210 code standards for site-built and manufactured homes, and the life expectancy rating of 195 home components. Available at amazon.com for $19.95.
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