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site-built, mobile/manufactured and modular homes
Should I add a plastic sheet vapor barrier on the ground under my mobile home?
Friday, August 24, 2018
Moist ground and standing water under a mobile home generate water vapor that accumulates in the crawlspace and can rise up into the home, slowly damaging the structure over time. The single most important part of installing a home to avoid moisture problems is grading the site so that water drains away from the home on all sides.
But the soil can hold a lot of moisture, even in a well-graded site, and spreading a ground cover sheet as a vapor barrier over the soil under a home is highly effective at moisture control. HUD and manufacturers both require new homes to have a vapor barrier if it will be enclosed with skirting or other materials. Florida’s Rule 15C, which covers covers installation of used homes, does not require a vapor barrier; but installing one is high recommended.
If you are experiencing wet soil under your home, consider adding a ground cover. Installation is simple, and can be done even years later. Cover 100% of the ground under the home with 6-mil polyethylene sheeting. Sealing the joints is not necessary, as an overlap of 12-inches is sufficient.
Also, it is not necessary to seal the ground cover around each pier if you are retrofitting it under an existing home. Just place the edges of the sheeting up against the pier base and cut back to fit. The work does not have to be perfect. It just needs to minimize the surface area of soil under the home that is emitting water vapor.
To find out the specific HUD requirements for new home installation for what they call a “vapor retarder material,” see our blog post Is a ground cover vapor barrier (plastic sheet) required under a new mobile/manufactured home? and When did a ground cover vapor barrier (plastic sheet) become required under a mobile/manufactured home?
To learn more ways of controlling moisture in your manufactured home, we suggest clicking the link below to download and read a guide prepared by the Manufactured Home Research Alliance, entitled “Moisture Problems in Manufactured Homes - Understanding Their Causes and Finding Solutions.”
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