How To Look At A House
McGarry and Madsen's home inspection blog for buyers of
site-built, mobile/manfuactured and modular homes
How do I stop water from getting under my mobile home?
Wednesday, April 8, 2020
Puddles of water or muddy ground under a mobile home are caused by either a plumbing leak or a poorly graded site that allows rainwater to run under the home. Long-term lumbing leaks can be avoided by pulling up a few panels of skirting to check under the home every few months. Inadequate drainage, though, is a bigger problem that could have been built-in at the time of installation or the result of site deterioration over time. The simple principle behind prepping a site for a mobile home is that any rainwater flow should be diverted around and away from the home.
Poor site drainage also creates a second problem: because most manufactured homes in Florida are set on piers of stacked concrete blocks over a plastic or precast concrete foundation pads sitting on top of the ground, any water movement under the home will also wash away soil under the pads over time and cause a gradual leaning, then failure of the piers in the affected area.
A home on a sloped site should never be installed without site preparation. It is not uncommon for us to find shallow washout channels grooved into the soil under homes on a sloped site with inadequate site prep.
The diagram above shows the way rain water should drain around a home on sloped ground, with a minimum slope of 1/2-inch per foot for the first 10 feet away from the foundation. And the simplest way to achieve drainage away from the home is to create a raised pad for it, as shown in the diagram below.
But when you have an existing home on level or mildly sloped ground without a raised pad, an alternative solution is to add gutters and drainage swales to carry rainwater away from the home, like the diagram below.
Ideally, a home on sloped ground should have both a dirt pad and drainage swale, as in the following diagram.
In some areas, wet ground under the home is impossible to avoid during the rainy season. The installation of a moisture barrier on the ground under the home can help reduce the wetness and the resulting moisture rising up to the bottom of the home at the bellyboard (sheet plastic material that seals the bottom of the home). Repairing any openings in the bellyboard will also help to reduce the moisture.
The plastic sheeting, typically 6-mil Visqueen, does not have to be sealed at adjoining pieces. A 12-inch overlap is sufficient.
Once in a blue moon, we come across a home that is so poorly sited that is it just about impossible to fix. We inspected a foreclosure mobile home in Old Town, Florida, several years ago that was pit-set (installed so that the floor is close to ground level, to look more like a site-built home, with a pit dug under it for access) in a low-lying area where the water table rises up to just below grade in the rainy season.
The bank had posted warnings on both entry doors that the home had a mold infestation, and when we opened the skirting it was clear why: the pit under the home had become a 12-inch deep pond. Mold had ravaged the interior of the home to the point where repair would not be cost-effective compared to replacing it.
But, unless your moisture problem is as severe as that foreclosure mobile, there is a moisture-management solution that will eliminate the wet ground. We suggest calling a reputable, Florida-licensed mobile home installer for further evaluation and repair of the problem.
Also, see our blog posts How do I look for yard drainage problems when buying a house? and What are the most common defects in mobile/manufactured home foundation piers? and Is it safe to go under a mobile home?
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Here’s links to a collection of our blog posts about MOBILE/MANUFACTURED HOMES:
Note: All diagrams are from the “Installation Course for Manufactured Housing” manual for installer licensing, Florida Department of Highway Safety and Motor Vehicles.
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