Insulation and air sealing for Lake St. Louis homes: attics, crawl spaces, rim joists and walls, starting with a free assessment of the R-value you actually have. Lake St. Louis enforces the 2015 IECC, which sets R-49 for a new attic.
Lake St. Louis runs to about 9.3 square miles and roughly 16,707 people. It sits about 34 miles northwest of downtown St. Louis. Around 7,657 housing units sit inside those boundaries. The community dates back to 1975. We cover ZIP code 63367.
No completed job in Lake St. Louis is logged in our records yet, and this page will say so until one is.
The typical home in Lake St. Louis dates to around the early-2000s. 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.
A planned lake community developed from initial 1961 planning and 1975/1977 incorporation onward; the city had very little commercial development until growth accelerated after 2004, so its housing skews newer within the metro.
That includes Harbor Town and The Meadows at Lake St. Louis. Housing age and construction shift across Lake St. Louis, sometimes by decades within a few streets, which is why we look in the attic before quoting rather than after.
The community is built around two private lakes owned by the Lake St. Louis Community Association; not all residents have lake-access membership. It faced annexation pressure from O'Fallon (east) and Wentzville (west) before incorporating.
The Census Bureau estimates 7,657 homes in Lake St. Louis. 0 of them (0%) went up before 1940 — one of the five lowest pre-1940 shares among the 44 places on this site. The 2000s were the busiest decade, adding 1,944 of today's homes (25%); 19% predate 1980 and 50% were built in 2000 or later. For St. Charles County as a whole the pre-1940 share is 2%, so Lake St. Louis sits below it.
Of 7,351 occupied homes, 63% heat with utility gas and 35% with electricity. Electric heat here is more common than across the county (30%), and ranks 20th of 44 on this site. Whoever comes out will ask about the furnace or heat pump first, since the heating fuel and the utility named on the bill settle which program money is on the table.
76% of occupied homes are owner-occupied and 67% of all homes are single-family detached houses. With houses like these, the conversations we expect most are about air sealing on newer houses that already have depth and an energy assessment before deciding what to fix first.
| Built | Homes | Share | |
|---|---|---|---|
| Before 1940 | 0 | 0% | |
| 1940s | 0 | 0% | |
| 1950s | 4 | 0% | |
| 1960s | 332 | 4% | |
| 1970s | 1,151 | 15% | |
| 1980s | 1,169 | 15% | |
| 1990s | 1,177 | 15% | |
| 2000s | 1,944 | 25% | |
| 2010s | 1,133 | 15% | |
| 2020 or later | 747 | 10% |
7,657 homes, Census ACS 2020–2024 (B25034, B25040, B25003); 7,351 occupied.
3,824 of Lake St. Louis' 7,657 homes (50%) were built in 2000 or later. Depth is rarely what is missing in houses this new; air paths are: attached garages, bonus rooms over them, the chase around a high-efficiency flue, and the thin edge where blown fiber meets the wall plate. They usually earn their money back on sealing rather than on more fiber.
Lake St. Louis enforces the 2015 IECC. Section 500.010(A)(1) adopts the 2021 editions of the International Building Code, International Residential Code, International Fire Code and the rest of the I-Code family, plus the 2020 National Electrical Code, by Ordinance No. 4726 effective 1-21-2025. Section 500.010(A)(3)(a)(2) then states that all references to the 2021 International Energy Conservation Code are replaced with reference to the 2015 International Energy Conservation Code. Section 500.010(A)(3)(b)(46) deletes all sections of Chapter 11 of the 2021 International Residential Code, so the 2015 IECC is the operative energy code for houses.
Under that edition the required attic value for new work here is R-49, and walls R-20 or R-13 + R-5 continuous. For comparison, the Department of Energy recommends R60 for an uninsulated attic in climate zone 4A, where Lake St. Louis sits, and R49 where there are already a few inches up there.
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. Lake Saint Louis substitutes the 2015 IECC for the 2021 edition without amending this table.
Nothing Lake St. Louis publishes settles this. Its permit lists name the work types it cares about, and insulation is not among them in either direction. The building permits page routes applications through the Citizenserve portal and does not list permit types or exemptions. The code's permit exemptions in Section 500.010(A)(3)(a)(7) cover retaining walls under 4 feet, sidewalks and driveways under 30 inches, painting, non-fixed fixtures under 5 feet 9 inches, and certain portable electrical, gas and mechanical appliances. Insulation is not named on either side. So we ask the department directly before the first day on site, and whatever comes back, pulling it is our job rather than yours.
The published number is 636-625-1200. The department page is here.
Permitting is on us, not on you.
Most Lake St. Louis 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 North East Community Action Corp. (NECAC) (573-324-2231) for free weatherization instead. The full program rules are on the St. Charles County page and in the rebate guide.
Every layer of an insulated attic, explained
Lake St. Louis borders O'Fallon, MO and Wentzville. These are the ones we also cover, each with its own energy code and permit rule:
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. |
|---|---|---|---|---|
| Lake St. Louis | 2015 IECC | R-49 | Not published | 636-625-1200 |
| Wentzville | Not published | — | Not published | 636-327-5101 |
| Cottleville | 2021 IRC ch. 11 | R-38 | Not published | 636-498-6565 |
| 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 |
All 6 St. Charles County jurisdictions side by side →
Lake St. Louis 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: Lake St. Louis names neither a permit nor an exemption for insulation, so one call to the department at 636-625-1200 settles it first.
For most Ameren Missouri customers, Pay As You Save: $0.20 per square foot on an attic starting at R-20 or lower and $0.06 per square foot on air sealing in 2026, the rest repaid on the bill. The federal 25C credit ended for work placed in service after December 31, 2025.
The typical home in Lake St. Louis dates to around the early-2000s; the Census Bureau's 2020-2024 median year built is 2000. Of its 7,657 homes, 0% went up before 1940 and 50% 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 · lakesaintlouis.com (2, 3) · energycodes.gov · en.wikipedia.org · bestplaces.net · ameren.com (2, 3, 4) · energystar.gov · data.census.gov. These change; confirm with the building department at 636-625-1200 or your electric utility first.
Free assessment: what depth you have now, what it has settled to, and what the sealing is worth.
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