Mold in Mobile Homes and Trailers: The Belly, the Skirting and the Ground Underneath

By John Calhoun, owner of Mold Remediation Gettysburg PA · Updated October 20, 2026

I like mobile home and trailer jobs. They’re honest problems: the water usually comes from a short list of places, you can get under the home to see it, and once the source is fixed the work is usually an easier in-and-out job than a house with a finished basement. Mobile homes are a real share of local housing, too. The Census counts about 1 in 11 homes in Cumberland Township and about 1 in 15 in Straban as mobile homes, and 2,388 across Adams County.

Where the water comes from

Plumbing under the floor. Supply lines and drains run through the floor and the underbelly. A slow drip from a fitting or a drain soaks the insulation inside the belly and can sit there for months. You’ll often notice a soft spot near the bathroom or kitchen before you notice anything else.

The ground. Bare soil under a home gives off moisture all the time. If the space under the home is closed in with skirting, that damp air has nowhere to go but up into the floor.

The skirting. Skirting with no vents, or vents that are blocked, buried or closed year-round, traps moisture under the home.

Things that drain underneath. Condensate from the air conditioner or furnace, a water heater relief line, or a dryer vent that dumps under the home instead of outside all add water right where you don’t want it.

Inside the home. Showers, cooking and laundry in a smaller space put a lot of moisture into the air. On cold winter walls and windows, it condenses.

What the installation standards say

HUD’s model installation standards for manufactured homes, in the federal regulations, are clear on the two things that matter most underneath:

• Cover the ground. If the space under the home is enclosed with skirting, a vapor retarder must cover the ground under the home: at least 6-mil polyethylene, covering the whole area except under open porches and decks, with joints overlapped at least 12 inches and tears repaired.
• Vent the skirting. Skirted crawl spaces need ventilation openings of at least 1 square foot for every 150 square feet of floor, or 1 for every 1,500 square feet when a vapor retarder covers the whole ground. Openings go on at least two opposite sides, as high as practical, with covers that can be adjusted in freezing climates.

The same section says dryer vents and combustion air inlets have to pass through the skirting to the outside, and drain water from the furnace, air conditioner or water heater has to be directed away from under the home. Those standards cover how a home is installed. An older home, or one that’s been worked on since, may not match them, which is exactly why it’s worth a look underneath.

What I check

1. Floors and lower walls inside, with a moisture meter, starting at the bathroom, kitchen and laundry.
2. The belly. Sagging, torn or patched bottom board, and wet insulation behind it.
3. The ground cover. Is there plastic, does it cover everything, and is it torn or buried?
4. The skirting vents. Are there enough, are they open, and are they on opposite sides?
5. Anything draining under the home. Condensate lines, relief lines and the dryer vent.
6. The plumbing itself, once the wet area is found.

What the fix usually looks like

Fix the leak first. Then remove the wet belly insulation, dry and check the floor framing, clean or replace what grew mold, and close the bottom board back up. Put down a proper ground cover and make sure the skirting breathes. Inside, run the bath fan, vent the dryer outside, and keep winter humidity in check. The CDC’s cleanup page covers protective gear if you’re doing any of it yourself.

An easier job than you’d think

A soft floor in a trailer feels like a disaster. Usually it’s a leak, some wet insulation and a short, contained job. I’m John Calhoun, and I’m glad to take these calls. See my mold remediation work and the overview of mold remediation in Gettysburg, PA, and for the crawl space side of things, vapor barrier vs. encapsulation and mold on joists and subfloor. Local housing numbers are on the Gettysburg housing data page.