Leaks Under a Mobile Home: Belly Wrap, Subfloor and Drying

The belly wrap, also called the bottom board, is the fabric or plastic barrier under a mobile home that holds insulation and protects the plumbing and ducts. When a pipe leaks under the floor, water collects in the belly wrap and makes it sag. Shut off the water, drain the belly at its lowest point, fix the leak, then dry or replace the insulation and subfloor.

What is a mobile home belly wrap?

Under the floor of a manufactured home is a sealed cavity. It holds insulation, water supply lines, drain lines and often the heating and cooling ducts. The belly wrap, or bottom board, is the material stretched across the bottom of the frame to close that cavity. It keeps out rodents, moisture and cold air, and holds the insulation in place.

The problem is that it also holds water. A leak inside the floor cavity has nowhere to go, so water pools in the belly wrap until it sags, tears or overflows.

What are the signs of a leak under a mobile home?

• The belly wrap sags or bulges, often in one spot
• Water dripping from the underside of the home
• Soft, spongy or uneven floors, especially near the kitchen, bathroom or water heater
• A musty smell inside, even with no visible water
• A water bill that rises with no change in use
• A water meter that moves with every fixture turned off
• Mold or staining on baseboards and lower walls

Apache Junction has more than 100 mobile home and RV communities, and leaks like these are among the most common water damage calls in 55+ parks.

What causes leaks under a mobile home?

• Supply line fittings under sinks, tubs and the water heater, especially older polybutylene or worn connections.
• Drain lines that loosen or crack as the home settles.
• Water heater failures in interior closets, which send water straight into the floor.
• AC condensate draining under the home instead of away from it.
• Freezing on cold nights, more likely in foothill areas like Queen Valley.
• Heat stress on plastic lines and fittings during long Arizona summers.

How do you fix a leak in the belly wrap?

1. Shut off the water at the home's main valve, often near the front under the home.
2. Drain the belly. Place a bucket or tarp, then make a small slit at the lowest point of the sag to let water out slowly. Expect insulation to come with it.
3. Open the belly enough to reach and repair the leaking line.
4. Remove soaked insulation. Wet fiberglass in a sealed belly will not dry well and can grow mold.
5. Dry the floor cavity. Use air movers and a dehumidifier, and check the subfloor with a moisture meter.
6. Check the subfloor. Particleboard that has swollen or crumbled must be replaced, often with plywood.
7. Replace insulation and patch the belly with bottom-board patch material and tape once everything is dry.

Why are manufactured homes harder to dry?

The floor cavity is closed on all sides, so water and humidity stay trapped. Many older manufactured homes use particleboard subfloors, which swell and lose strength when wet, unlike plywood. Skirting around the home can also trap humid air underneath. Drying usually means opening the belly, moving air through the cavity and venting the skirting, not just drying the carpet inside.

How do you protect a seasonal mobile home from leaks?

• Shut off the main water valve and drain the lines before leaving for the summer. Our full snowbird checklist covers the rest.
• Turn off the water heater or set it to vacation mode.
• Ask a neighbor or park manager to look under the home after big storms.
• Check the belly wrap each fall for sags, tears or rodent damage.
• Make sure the AC condensate line drains outside the skirting.

If you find a musty smell when you return, read how to find the cause of a musty smell. If the leak came from the water heater, see why water heaters leak.