Attic insulation, air sealing, crawl spaces and walls for homes in St. Charles — starting with a free assessment that measures the R-value you actually have. St. Charles enforces the 2015 IECC, which sets R-49 for a new attic.
St. Charles runs to about 26 square miles and roughly 72,458 people. It sits about 20 miles northwest of downtown St. Louis. Around 32,305 housing units sit inside those boundaries. The community dates back to 1809. We cover ZIP codes 63301, 63302, 63303 and 63304.
No completed job in St. Charles is logged in our records yet, and this page will say so until one is.
The typical home in St. Charles dates to around the mid-1980s. Houses of this vintage usually got batts or blown fiber at whatever the standard of the day was, which is well short of what is recommended now. Most are one top-up away from being right.
Historic riverfront/Main Street core (St. Charles Historic District, Frenchtown Historic District) has buildings mostly from the 1830s-1940s in Greek Revival, Italianate and Late Victorian styles.
That includes Frenchtown and New Town. Housing age and construction shift across St. Charles, sometimes by decades within a few streets, which is why we look in the attic before quoting rather than after.
St. Charles was Missouri's first state capital (1821-1826); its historic districts hold over a hundred structures spanning the state's early statehood period, while New Town is a modern New Urbanist-style planned development.
The Census Bureau estimates 32,305 homes in St. Charles. 2,192 of them (7%) went up before 1940 — 19th of 44 places on this site for pre-1940 housing. The 1980s were the busiest decade, adding 5,831 of today's homes (18%); 38% predate 1980 and 28% were built in 2000 or later. For St. Charles County as a whole the pre-1940 share is 2%, so St. Charles sits above it.
Of 30,362 occupied homes, 63% heat with utility gas and 35% with electricity. Electric heat here is more common than across the county (30%), and ranks 19th of 44 on this site. That is why the assessment asks how the house is heated: the fuel and the name on the utility bill decide which program, if any, can pay toward the work.
68% of occupied homes are owner-occupied and 59% of all homes are single-family detached houses, with 1,674 mobile homes in the count. On a housing mix like this, the likely starting points are an energy assessment before deciding what to fix first.
| Built | Homes | Share | |
|---|---|---|---|
| Before 1940 | 2,192 | 7% | |
| 1940s | 628 | 2% | |
| 1950s | 2,575 | 8% | |
| 1960s | 3,216 | 10% | |
| 1970s | 3,788 | 12% | |
| 1980s | 5,831 | 18% | |
| 1990s | 5,112 | 16% | |
| 2000s | 4,051 | 13% | |
| 2010s | 3,896 | 12% | |
| 2020 or later | 1,016 | 3% |
32,305 homes, Census ACS 2020–2024 (B25034, B25040, B25003); 30,362 occupied.
10,943 of St. Charles' 32,305 homes (34%) were built in the 1980s and 1990s. The gaps in houses of that age are the parts nobody sealed: batts stuffed into the rim joist, bare spots over cathedral and tray ceilings, soffit vents buried with no baffles, can lights punched through the ceiling plane. A top-up plus a day of sealing usually covers it.
St. Charles enforces the 2015 IECC. Chapter 500, Article V of the City of Saint Charles code adopts by reference the 2015 Edition of the International Energy Conservation Code. The current adopting language comes from Ord. No. 15-102 Section 3, dated 5-19-2015, replacing the original adoption in Ord. No. 05-153 of 5-27-2005. The city's own Adopted Building Codes page lists the 2021 IBC, 2021 IRC, 2021 IEBC, 2021 IPC, 2021 IMC, 2021 IFGC, 2021 ISPSC, 2020 NEC and the 2015 IECC, so the energy code is one cycle behind the rest of the code set.
For new work, the attic number under that edition is R-49, with walls at R-20 or R-13 + R-5 continuous. Set that against the Department of Energy, which recommends R60 for an uninsulated attic in this climate zone and R49 for one that already has a few inches.
Table R402.1.2 of the 2015 IECC, climate zone 4 except Marine, as reprinted in the U.S. Department of Energy Building Energy Codes Program summary of 2015 IECC residential requirements. The city adopts this table without amendment.
Nothing St. Charles publishes settles this. Its permit lists name the work types it cares about, and insulation is not among them in either direction. The city's permit fee schedule has no insulation, weatherization, air sealing or energy line; residential work is billed under a single 'Integrated permit - residential' fee of the greater of $50.00 or estimated construction cost times the permit fee multiplier. The building code's permit exemption list in Section 500.050(A)(3) names detached accessory structures under 144 square feet and fences under 6 feet, and does not mention insulation either way. So we ask the department directly before the first day on site, and whatever comes back, pulling it is our job rather than yours.
Not published for insulation contractors. St. Charles County issues business licenses for plumbing, electrical and mechanical contractors under County Code Chapters 631, 632 and 633; neither code library shows a city or county registration for insulation contractors.
The published number is 636-949-3200. The department page is here.
Permitting is on us, not on you.
St. Charles 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. For every condition attached, see the St. Charles County page or the rebate guide.
Every layer of an insulated attic, explained
Elsewhere in St. Charles County we also cover:
Missouri sets none of this at state level. Across the 6 places in this table there are 3 different adopted editions (2015 IECC, 2021 IECC and 2021 IRC ch. 11), and none of the 6 publishes a permit rule for insulation.
| City | Energy code | Attic R required | Permit to insulate | Building dept. |
|---|---|---|---|---|
| St. Charles | 2015 IECC | R-49 | Not published | 636-949-3200 |
| 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. Peters | 2021 IRC ch. 11 | R-38 | Not published | 636-477-6600 ext. 1670 |
| Wentzville | Not published | — | Not published | 636-327-5101 |
All 6 St. Charles County jurisdictions side by side →
St. Charles enforces the 2015 IECC, which sets R-49 for an attic in new work. That code also reaches work on existing houses, not only new ones.
Not on paper: St. Charles names neither a permit nor an exemption for insulation, so one call to the department at 636-949-3200 settles it first.
Ameren Missouri's Pay As You Save: $0.20 per square foot for an attic starting at R-20 or below and $0.06 per square foot for air sealing in 2026, with the balance on the electric bill. The federal 25C credit ended for work placed in service after December 31, 2025.
The typical home in St. Charles dates to around the mid-1980s; the Census Bureau's 2020-2024 median year built is 1986. Of its 32,305 homes, 7% went up before 1940 and 28% in 2000 or later. It is a median for the place, not a survey of individual houses.
Code and permit facts checked September 10, 2026, rebates October 24, 2026; housing: Census ACS 2020–2024. Sources: ecode360.com (2, 3, 4) · stcharlescitymo.gov (2, 3) · energycodes.gov · en.wikipedia.org (2, 3) · censusreporter.org · city-data.com · ameren.com (2, 3, 4) · energystar.gov · data.census.gov. These change; confirm with the building department at 636-949-3200 or your electric utility first.
Free assessment, a measured R-value, and photos you keep either way.
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