Manufactured & Mobile Home Insulation: R-Values and Retrofit Tips
Manufactured homes aren't built to local residential energy code — they're built to the federal HUD Code, which uses its own thermal zone map and R-value standards. Here's how that works, and what to know if you're retrofitting an older unit.
HUD's three thermal zones
Unlike the IECC's climate zones used for site-built homes, HUD Code manufactured housing (24 CFR Part 3280) is designed to one of three thermal zones based on latitude:
| HUD Zone | General Region | Description |
|---|---|---|
| Zone I | Southern U.S. — Florida, Gulf Coast, Southern California, etc. | Warmest, lowest insulation requirement |
| Zone II | Mid-latitude states — much of the central and mid-Atlantic U.S. | Moderate |
| Zone III | Northern U.S. — northern tier states, mountain regions | Coldest, highest insulation requirement |
Typical factory-installed R-values by zone
| Assembly | Zone I | Zone II | Zone III |
|---|---|---|---|
| Ceiling/roof | R-14 | R-19 | R-22 to R-33 |
| Walls | R-11 | R-11 | R-14 to R-19 |
| Floor (belly) | R-11 | R-14 | R-22 |
These are the standards the home was originally built to at the factory. If you're insulating a manufactured home yourself — for a repair, an addition, or a retrofit — match or exceed the value for your zone rather than assuming a one-size answer.
Retrofit: skirting and underbelly insulation
The most common insulation project on an existing manufactured home isn't the walls or roof — it's the underside. A few things worth knowing:
- Skirting alone isn't insulation. Skirting blocks wind and pests around the home's perimeter, but it doesn't add meaningful R-value on its own. Insulated skirting panels or adding batt insulation to the belly above the skirting is what actually improves floor performance.
- The belly board matters. The factory-installed underbelly is a fabric or board barrier holding floor insulation in place and keeping out moisture and pests. If it's torn or sagging, floor insulation underneath is often wet, compressed, or missing — that's usually the real cause of cold floors, not an underlying lack of R-value.
- Batt width often differs from stick-built framing. Manufactured home wall and floor framing can use narrower or non-standard spacing than a site-built house — confirm actual cavity width before ordering rather than assuming standard 16" o.c. batt width.
Product notes for manufactured home jobs
Unfaced or kraft-faced fiberglass batts are the standard product for both new manufactured home construction and retrofit work, sized to the specific cavity being filled. For belly/floor retrofits where the space is being accessed from underneath, easier-to-handle faced batts or rolls are typically preferred over rigid materials.
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