Attic insulation, air sealing and crawl space work across St. Charles County. We cover 6 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 167,163 homes, 2% were built before 1940, and 30% 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. |
|---|---|---|---|---|
| Cottleville | 2021 IRC ch. 11 | R-38 | Not published | 636-498-6565 |
| Lake St. Louis | 2015 IECC | R-49 | Not published | 636-625-1200 |
| O'Fallon | 2021 IECC | — | Not published | 636-379-5660 |
| St. Charles | 2015 IECC | R-49 | Not published | 636-949-3200 |
| St. Peters | 2021 IRC ch. 11 | R-38 | Not published | 636-477-6600 ext. 1670 |
| Wentzville | Not published | — | Not published | 636-327-5101 |
5 of the 6 publish an energy code edition we could name and 4 of the 6 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 St. Charles County the code is whatever each jurisdiction adopted on its own: the 2021 IRC ch. 11 in Cottleville and St. Peters; the 2015 IECC in Lake St. Louis and St. Charles; the 2021 IECC in O'Fallon; no published edition in Wentzville.
The attic figures that follow from those editions, for new work: R-38 in Cottleville and St. Peters; R-49 in Lake St. Louis and St. Charles. A specification that was right one town over is not automatically right here, which is why each place has its own page.
The 6 places here with their own Census row hold 120,601 of St. Charles County's 167,163 homes (72%); the rest are in other municipalities or unincorporated areas.
One detail worth knowing before a job in each of them:
St. Charles County has 167,163 homes in the Census count, with a median year built of 1994. 25% were built before 1980 and 39% in 2000 or later; the single biggest decade was the 2000s, with 35,465 homes (21%). Of 161,311 occupied homes, 66% heat with utility gas and 30% with electricity.
Across the 6 places we cover here, St. Charles has the oldest housing (7% before 1940) and Cottleville the newest (81% built in 2000 or later). O'Fallon is the largest, at 36,206 homes, and Lake St. Louis has the most electric heat (35%).
| Place | Homes | Before 1940 | Median built | Electric heat | Owner-occupied |
|---|---|---|---|---|---|
| O'Fallon | 36,206 | 1% | 2000 | 27% | 81% |
| St. Charles | 32,305 | 7% | 1986 | 35% | 68% |
| St. Peters | 25,557 | 1% | 1988 | 29% | 79% |
| Wentzville | 16,601 | 1% | 2008 | 34% | 82% |
| Lake St. Louis | 7,657 | 0% | 2000 | 35% | 76% |
| Cottleville | 2,275 | 1% | 2012 | 28% | 81% |
Against the eight-county metro on this site (1,177,290 homes), St. Charles County's pre-1940 share of 2% compares with 16%, and its electric-heat share of 30% with 32%. 5,338 occupied homes (3%) burn propane or other tank gas and 382 (0%) heat with wood, which matters because neither fuel comes with a gas utility's program attached. 81% of occupied homes are owner-occupied and 75% of all homes are single-family detached houses.
In St. Charles County that adds up to 36,364 homes from the 1950s to the 1970s, the usual candidates for an attic top-up; 64,975 built since 2000, where air sealing tends to matter more than extra depth.
| Built | Homes | Share | |
|---|---|---|---|
| Before 1940 | 3,646 | 2% | |
| 1940s | 1,373 | 1% | |
| 1950s | 6,347 | 4% | |
| 1960s | 10,291 | 6% | |
| 1970s | 19,726 | 12% | |
| 1980s | 28,267 | 17% | |
| 1990s | 32,538 | 19% | |
| 2000s | 35,465 | 21% | |
| 2010s | 24,017 | 14% | |
| 2020 or later | 5,493 | 3% |
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.
St. Charles County is on the Missouri side, where most addresses buy their electricity from Ameren Missouri. Its 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; the incentive comes off the cost and the rest is repaid through a monthly charge on the 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 North East Community Action Corp. (NECAC) (573-324-2231) for free weatherization instead. The full program rules are in the rebate guide.
Nothing published settles it. None of the 6 jurisdictions we cover in St. Charles 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 St. Charles County are R-38 in Cottleville, St. Peters; R-49 in Lake St. Louis, St. Charles. 2 of the 6 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 2% of St. Charles County's 167,163 homes before 1940 and 25% before 1980, with a median year built of 1994.
For most addresses across St. Charles 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 North East Community Action Corp. (NECAC) runs for St. Charles County (573-324-2231). If the household income qualifies, the work can be free rather than discounted.
Free assessment, a measured R-value, and photos you keep either way.
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