How To Look At A House
McGarry and Madsen's home inspection blog for buyers of
site-built, mobile/manufactured and modular homes
Does mobile home skirting have to be ventilated?
Wednesday, October 3, 2018
Yes, it does. Ventilation of the crawl space is just as important for a manufactured home as a site-built home, and lack of ventilation causes similar problems to both: wood rot of the floor framing, warped floor boards, and mold growth.
The skirting itself is necessary for two reasons: to keep rodents and other nuisance animals out of the crawl space and because mortgage lenders require it as prerequisite for loan approval. But air flow through the skirting is necessary to carry away the moisture that is constantly rising out of the soil under the home.
The standard prescription for ventilation is one square inch of ventilation opening for every square foot of floor space of the home. Skirting with built-in ventilation holes is available or you can install solid decorative skirting, such as simulated brick or rock, and cut-in the required vents at regular intervals. The ventilation openings should be evenly distributed on all four sides of the home to get the necessary cross-ventilation air flow. Also, be sure to place a vent within 3-feet of each corner to prevent any “dead air” pockets in the corners, and don’t block the vents with stored items in front of them later.
When you see a mobile with solid skirting all around, like in the photo below, expect to find wet soil and high humidity in the crawl space under the home.
While skirting ventilation is important, it’s just one part of keeping the underside of a manufactured home dry and secure. We recommend that you check the crawl space regularly, looking for any of these potential problems:
1) A clothes dryer vent that terminates under the home dramatically raises humidity levels. Make sure the dryer vent duct has a louvered termination panel at skirting or beyond, and that there are not tears in the duct run.
2) Tears in the belly board (also called belly wrap, which is the plastic sheet that seals the underside of the home) leave the home open to moisture intrusion coming up through the floor. Open the skirting at a few points around the perimeter, and do a quick scan of the underside of the home with a flashlight. Follow up with repairs as necessary. We typically see openings in the belly board where minor plumbing repairs have been done under the floor and the belly board has not been resealed securely.
3) A plumbing leak can also cause problems under the home. Big water pipe leaks make a mess quickly and get noticed right away. But a pinhole leak can go unnoticed for months, while soaking the insulation under the floor and slowly spreading. When checking under the home, look for any bulges in the belly board, which is the first indication of this problem.
4) Gaps in the skirting, sizable damage holes, or an access hatch that is left ajar will allow critters under home that pull down areas of belly board and insulation, along with damaging ducts. Keep the skirting zipped up.
5) Bad site drainage can make the ground under a home muddy or, even worse, allow ponding water during the rainy season. A properly graded site, with the ground sloping away from the crawl space on all sides, is important. If you find that the ground under your home remains wet for long periods, consult a professional contractor for a solution.
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