Attic insulation, air sealing and crawl space work across Jefferson County. We cover 3 jurisdictions here, each with its own page: the energy code that applies, the attic R-value it requires, the permit position and the building department's number. Of the county's 93,955 homes, 3% were built before 1940, and 58% of occupied homes heat with electricity.
Click a city for its full code, permit and rebate detail.
| City | Energy code | Attic R required | Permit to insulate | Building dept. |
|---|---|---|---|---|
| Arnold | 2021 IECC | — | Not published | 636-282-2378 |
| Festus | Not published | — | Not published | 636-937-6646 |
| Imperial | 2015 IECC | R-49 | Not published | 636-797-5555 |
2 of the 3 publish an energy code edition we could name and 1 of the 3 a required R-value we could read; a blank in this table means the jurisdiction publishes nothing, not that we guessed.
Missouri sets no statewide residential energy code, so across Jefferson County the code is whatever each jurisdiction adopted on its own: the 2021 IECC in Arnold; the 2015 IECC in Imperial; no published edition in Festus.
The attic figures that follow from those editions, for new work: R-49 in Imperial. A specification that was right one town over is not automatically right here, which is why each place has its own page.
The 3 places here with their own Census row hold 16,481 of Jefferson County's 93,955 homes (18%); the rest are in other municipalities or unincorporated areas.
One detail worth knowing before a job in each of them:
Jefferson County has 93,955 homes in the Census count, with a median year built of 1987. 41% were built before 1980 and 29% in 2000 or later; the single biggest decade was the 2000s, with 16,786 homes (18%). Of 88,309 occupied homes, 32% heat with utility gas and 58% with electricity.
Across the 3 places we cover here, Festus has the oldest housing (9% before 1940) and Imperial the newest (35% built in 2000 or later). Arnold is the largest, at 8,982 homes, and Imperial has the most electric heat (62%).
| Place | Homes | Before 1940 | Median built | Electric heat | Owner-occupied |
|---|---|---|---|---|---|
| Arnold | 8,982 | 2% | 1977 | 31% | 80% |
| Festus | 5,539 | 9% | 1983 | 49% | 58% |
| Imperial | 1,960 | 4% | 1990 | 62% | 93% |
Against the eight-county metro on this site (1,177,290 homes), Jefferson County's pre-1940 share of 3% compares with 16%, and its electric-heat share of 58% with 32%. 6,314 occupied homes (7%) burn propane or other tank gas and 1,697 (2%) heat with wood, which matters because neither fuel comes with a gas utility's program attached. 82% of occupied homes are owner-occupied and 80% of all homes are single-family detached houses.
In Jefferson County that adds up to 32,497 homes from the 1950s to the 1970s, the usual candidates for an attic top-up; 27,444 built since 2000, where air sealing tends to matter more than extra depth.
| Built | Homes | Share | |
|---|---|---|---|
| Before 1940 | 3,256 | 3% | |
| 1940s | 2,348 | 2% | |
| 1950s | 8,670 | 9% | |
| 1960s | 9,880 | 11% | |
| 1970s | 13,947 | 15% | |
| 1980s | 12,712 | 14% | |
| 1990s | 15,698 | 17% | |
| 2000s | 16,786 | 18% | |
| 2010s | 8,627 | 9% | |
| 2020 or later | 2,031 | 2% |
Figures: U.S. Census Bureau, American Community Survey 2020–2024 5-year estimates (tables B25001, B25003, B25024, B25034, B25035, B25040). Survey estimates carry margins of error, widest in the smallest places. Census table.
Most Jefferson County addresses are Ameren Missouri electric customers, and Ameren Missouri pays toward insulation through Pay As You Save: $0.20 per square foot on the attic and $0.06 per square foot on air sealing in the 2026 program year, with the rest of the cost recovered through the electric bill. The conditions: an attic going from R-20 or below to at least R-38, air sealing that cuts measured leakage by 20 percent, and twelve months in the home. CommunitySavers can include attic insulation at no charge for income-eligible households. Income-qualified households can apply to Jefferson-Franklin Community Action Corp. (JFCAC) (636-789-2686) for free weatherization instead. The rebate guide carries the full rules.
Nothing published settles it. None of the 3 jurisdictions we cover in Jefferson County lists insulation as permit work or as exempt, so the answer comes from a call to the building department before the job starts. Each town page gives that department's number.
For new work, the published attic figures across Jefferson County are R-49 in Imperial. 2 of the 3 jurisdictions publish no figure we could read. The Department of Energy recommends R60 for an uninsulated attic in this climate zone.
The Census Bureau's 2020–2024 estimates put 3% of Jefferson County's 93,955 homes before 1940 and 41% before 1980, with a median year built of 1987.
For most addresses across Jefferson County the electric utility is Ameren Missouri, whose Pay As You Save program publishes $0.20 per square foot on ceiling and attic insulation and $0.06 per square foot on air sealing for the 2026 program year, with the rest of the cost repaid through the bill, and only where the attic starts at R-20 or below. For income-eligible households, CommunitySavers can include attic insulation at no charge.
Yes, through the Missouri low-income weatherization program, which Jefferson-Franklin Community Action Corp. (JFCAC) runs for Jefferson County (636-789-2686). If the household income qualifies, the work can be free rather than discounted.
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