Address all significant moisture problems before insulating. The most important single moisture-control measure is installing a ground-moisture barrier. See also Preparing for Foundation or Floor Insulation.
11.4.1 Mobile Home Floor Insulation
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SWS Details: 4.1302.1 Prepare Belly Floor Cavity for Insulation, 4.1303.1 Insulation of Floor Cavity with Blown Material, 2.0107.2 Basements and Crawl Spaces—Pre-Work Qualifications |
Mobile home floor insulation is a good energy-saving measure in cool climates. The original insulation is usually fastened to the bottom of the floor joists, leaving much of the cavity uninsulated and subject to convection currents. This greatly reduces the insulation’s R-value. Blown-in belly insulation also tends to control duct leakage.
Preparing for Mobile Home Floor Insulation
Prior to installing floor insulation, always perform these repairs.
✓ Repair plumbing leaks.
✓ Secure gas, water, and electrical lines at least every 4' to a floor joist or framing member.
✓ Tightly seal all holes in the floor.
✓ Inspect and seal ducts.
✓ Repair the rodent barrier.
✓ Install a ground-moisture barrier in the crawl space if the site is wet.
Patching the Belly
Mobile homes have two common types of belly covering: rigid fiber board and flexible paper or fabric. The fiberboard is normally stapled to the bottom of the floor joists. To patch a rigid belly, simply screw or staple plywood or another rigid material over the hole.
Flexible belly material may have no solid backing behind the hole or tear because the material forms a bag around the main duct, which is installed below the floor joists. In this case, use both adhesive and stitch staples to bind the flexible patch to the flexible belly material.
Insulating the Floor
Two methods of insulating mobile home floors are common. Blown fiberglass is recommended over cellulose for either method. MN WAP does not allow blowing cellulose in mobile home bellies.
1. Drilling through the 2-by-6 rim joist and blowing fiberglass through a rigid fill tube into the belly.
2. Blowing fiberglass insulation through a flexible fill tube or a rigid fill tube into the underbelly.
First repair all holes in the belly. Use mobile home belly-paper, silicone sealant, and stitch staples. Use these same patches over the holes cut for fill-tubes. Screw wood lath over weak areas if needed.
When blowing through holes from underneath the home, consider blowing through damaged areas before patching them.
Identify any plumbing lines, and avoid installing insulation between them and the living space if freezing could be an issue. This may require running a piece of belly-paper under the pipes, and insulating the resulting cavity, to include the pipes in the heated envelope of the home.
Unfaced fiberglass batts may also be used to insulate floor sections where the insulation and belly are missing. The insulation should be supported by lath, twine, or insulation supports. This is a good approach when it isn’t cost-effective to insulate the entire belly.
