Mobile Home
Insulation
Belly to Roof

It depends on the area. Blown insulation in the belly runs about $1,200–$2,500 (Mobile Home Friend). A Maine installer prices roof or ceiling insulation at $1,500–$3,000 and walls at $2,500–$4,000. HomeGuide puts insulated vinyl skirting at $1,500–$3,000 on a single-wide, and one vendor blog puts a full-home job at $5,900–$8,900.

It depends on the area. For the belly, MobileHomeLiving prefers blown fiberglass, and closed-cell spray foam is the option that also air-seals and resists moisture; open-cell foam should not go under the floor. Roofs are blown through the roof or covered with a roof-over, including a coated foam roof. Walls are rarely done: only 4% of weatherized mobile homes got wall insulation.

Floor insulation sits in the belly, closed by a bottom board of black woven polyethylene that also blocks rodents and moisture, with kraft-faced fiberglass above it. To add insulation, installers blow fiberglass or cellulose into the belly, replace batts, or remove the old material and spray closed-cell foam, then seal any openings in the bottom board.

Yes, with closed-cell foam. Building Science Corporation says vented crawlspaces require high-density closed-cell foam, and DOE says open-cell should not be used below ground level where it could absorb water. Fix plumbing leaks first, since foam can trap water from above, and ask whether exposed foam needs an ignition barrier.

HomeGuide prices closed-cell spray foam under a house at $2–$5 per sq ft, so a 70 by 14 ft floor (980 sq ft) runs roughly $1,960–$4,900. At Angi's September 2026 closed-cell range of $1.30–$3.10 per board foot, 2 inches on that floor is about $2,550–$6,080. Removing old insulation adds $0.75–$2.00 per sq ft.

Mobile Home Friend prices full R-19 batt replacement at $1,800–$4,500 installed or $1,000–$2,000 in DIY materials, and blown belly insulation at $1,200–$2,500. A Maine installer lists underbelly replacement at $1,500–$4,000 installed. For small repairs, one supplier sells a 70-foot roll of bottom board for about $140.

The HUD Code caps whole-home heat loss rather than setting cavity R-values: Uo 0.116 in Zone 1, 0.096 in Zone 2 and 0.079 in Zone 3, roughly R-8.6, R-10.4 and R-12.7 overall. ENERGY STAR's v3 targets are higher: R-22 floors in Zones 1 and 2, R-33 in Zone 3, and R-33 to R-38 ceilings.

Yes. The HUD Code requires exterior wall, floor and ceiling cavities to be insulated. The cavities are small: DOE notes pre-1976 walls often have only 2x2 studs, and one vendor blog describes 2.5–3.5 inch wall cavities with R-7 to R-11 fiberglass and roof cavities of about 2–4 inches.

On the roof, yes: a spray foam roof goes over the existing roof under a protective coating, once you've confirmed there are no leaks or underlying damage. Inside walls and ceilings, HUD allows foam plastic only when it's covered by 5/16 inch gypsum board or equivalent or the product passed HUD-accepted fire tests.

Insulated skirting is on DOE's retrofit list, and HomeGuide prices insulated vinyl at $1,500–$3,000 on a single-wide. It still needs vents: HUD requires 1 sq ft per 150 sq ft of floor, or 1 per 1,500 with a full 6-mil ground vapor retarder, on at least two opposite sides.

The federal Weatherization Assistance Program covers mobile homes. Households at or below 200% of the poverty level qualify, as do those with a member who received SSI or Title IV cash assistance in the past 12 months. DOE says weatherized households save an average of $372 or more a year. Some states add rebates.

Start where weatherization crews do: seal air leaks and ducts and fix the belly. Then consider floor and roof insulation, insulated skirting with proper vents, and storm windows. In an ORNL field study of 86 weatherized mobile homes, space-heating use dropped about 20%. Keep a 6-mil ground cover under the home.