Is a ground cover vapor barrier (plastic sheet) required under a new mobile/manufactured home?
Thursday, June 14, 2018
Yes, both the U.S. Department of Housing and Urban Development (HUD) and manufacturers’ installation manuals require a plastic sheet “vapor retarder material” on the ground under the home when the crawl space is enclosed by skirting or other materials. “The HUD requirement has been in place since October 20th of 2008,” according to Vickie Ladd. of the Manufactured Housing Section of the Florida Department of Highway Safety and Motor Vehicles. An exception is allowed when the home is installed in an area with dry soil conditions, and is not required to be retrofitted on an existing home.
Joints Can Be Overlapped
Joints in the material do not need to be sealed, as long as they are lapped at least 12-inches. The plastic sheeting can be placed beneath footing pads, over the pads, or around them, and must be fitted around any anchors or other obstructions.
Here’s the exact wording of HUD’s “Part 3285 - Model Manufactured Home Installations Standards.” It is a national minimum requirement and local jurisdictions are allowed to set higher standards.
§3285.204 Ground moisture control.
(a) Vapor retarder. If the space under the home is to be enclosed with skirting or other materials, a vapor retarder must be installed to cover the ground under the home, unless the home is installed in an arid region with dry soil conditions.
(b) Vapor retarder material. A minimum of six mil polyethylene sheeting or its equivalent must be used.
(c) Proper installation. (1) The entire area under the home must be covered with the vapor retarder, as noted in §3285.204(a), except for areas under open porches, decks, and recessed entries. Joints in the vapor retarder must be overlapped at least 12 inches.
(2) The vapor retarder may be placed directly beneath footings, or otherwise installed around or over footings placed at grade, and around anchors or other obstructions.
(3) Any voids or tears in the vapor retarder must be repaired. At least one repair method must be provided in the manufacturer's installation instructions.
The ground cover material must be a minimum of six-mil polyethylene sheeting (Visqueen® is a common brand), but no color requirement is specified. An alternative material may be allowed, if approved by local jurisdiction. The entire area under the home has to be covered, except at open porches, decks, and recessed entries.
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