Attic insulation, air sealing, crawl spaces and walls for homes in St. Peters — starting with a free assessment that measures the R-value you actually have. St. Peters enforces the 2021 IRC ch. 11, which sets R-38 for a new attic.
St. Peters runs to about 22 square miles and roughly 61,398 people. It sits about 30 miles northwest of downtown St. Louis. There are around 25,557 housing units here. The community dates back to 1910. We cover ZIP codes 63376, 63304, 63303 and 63366.
We have not logged a completed job in St. Peters yet. We would rather say so than put a number on this page that is not real.
The typical home in St. Peters dates to around the late-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.
St. Peters had under 500 residents as late as 1970 and grew to over 60,000 by the mid-2020s, meaning the overwhelming majority of the housing stock is 1970s-onward suburban construction with essentially no pre-suburban core.
St. Peters grew from 486 residents in 1970 to 15,700 by 1980 as St. Charles County suburbanized rapidly; it did not reach city status until 1959 after being a town since 1910.
The Census Bureau estimates 25,557 homes in St. Peters. 252 of them (1%) went up before 1940 — 38th of 44 places on this site for pre-1940 housing. The 1980s were the busiest decade, adding 7,831 of today's homes (31%); 25% predate 1980 and 25% were built in 2000 or later. For St. Charles County as a whole the pre-1940 share is 2%, so St. Peters sits below it.
Of 24,591 occupied homes, 69% heat with utility gas and 29% with electricity; another 2% burn propane or other tank gas. Electric heat here is less common than across the county (30%), and ranks 28th 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.
79% of occupied homes are owner-occupied and 68% of all homes are single-family detached houses, with 520 mobile homes in the count. With houses like these, the conversations we expect most are about an energy assessment before deciding what to fix first.
| Built | Homes | Share | |
|---|---|---|---|
| Before 1940 | 252 | 1% | |
| 1940s | 160 | 1% | |
| 1950s | 285 | 1% | |
| 1960s | 492 | 2% | |
| 1970s | 5,274 | 21% | |
| 1980s | 7,831 | 31% | |
| 1990s | 4,956 | 19% | |
| 2000s | 3,348 | 13% | |
| 2010s | 2,595 | 10% | |
| 2020 or later | 364 | 1% |
25,557 homes, Census ACS 2020–2024 (B25034, B25040, B25003); 24,591 occupied.
12,787 of St. Peters' 25,557 homes (50%) 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. Peters enforces the 2021 IRC Chapter 11 (Energy Efficiency), as amended; the 2021 IECC is adopted but its residential chapters are deleted. City Code Chapter 513 adopts the International Energy Conservation Code, 2021 Edition, by Ordinance No. 7912 of 12-21-2023. That same chapter then deletes every residential chapter of the IECC: item 11 deletes Chapter 1 (RE), item 12 Chapter 2 (RE), item 13 Chapter 3 (RE), item 14 Chapter 4 (RE) Residential Energy Efficiency, and item 15 Chapter 5 (RE) Existing Buildings. Residential energy requirements come instead from Chapter 11 of the 2021 International Residential Code, adopted in City Code Chapter 504 by the same Ordinance No. 7912 and amended in Section 504.040.
Under that edition the required attic value for new work here is R-38, and walls R-13. For comparison, the Department of Energy recommends R60 for an uninsulated attic in climate zone 4A, where St. Peters sits, and R49 where there are already a few inches up there.
Table N1102.1.3 as amended by City Code Section 504.040(A)(98), climate zone 4A. The amended row reads fenestration U-factor.35, ceiling 38, wood frame wall 13, basement wall 10ci or 13f, slab 10 at 2 ft, crawl space wall 10/13.
St. Peters publishes no answer either way. Insulation and air sealing appear on neither the permit-required list nor the exempt list. The city's licenses and permits page describes building permits for new construction, additions, remodels and repairs to electrical, mechanical and plumbing systems. Insulation, weatherization and air sealing are not listed. The IRC Section R105.2 exemption list adopted in Section 504.040 covers accessory structures under 120 square feet, fences under 6 feet, retaining walls under 4 feet, water tanks under 5,000 gallons, sidewalks, patios and driveways, finish work, shallow pools, playground equipment and window awnings, and does not mention insulation. We confirm it with the department before we start and pull whatever is needed. We would rather write that here than guess on your behalf.
Not published for insulation contractors. The adopted mechanical code Section M1201.2.90 points to City Code Section 515.050 for mechanical contractor licensing. The city code shows no registration or licensing provision covering insulation work.
The published number is 636-477-6600 ext. 1670. The department page is here.
Permitting is on us, not on you.
Most St. Peters 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. It counts only when the attic is at R-20 or below beforehand and R-38 or more afterward, when air sealing cuts measured leakage by 20 percent, and when the household has lived there for the past year; for income-eligible households, CommunitySavers can include attic insulation at no charge. 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. Peters | 2021 IRC ch. 11 | R-38 | Not published | 636-477-6600 ext. 1670 |
| 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 |
| Wentzville | Not published | — | Not published | 636-327-5101 |
All 6 St. Charles County jurisdictions side by side →
St. Peters enforces the 2021 IRC ch. 11, which sets R-38 for an attic in new work. Whether it reaches a retrofit of an existing house is not published.
St. Peters publishes no rule either way, so we ask its building department at 636-477-6600 ext. 1670 before the job is scheduled.
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. Peters dates to around the late-1980s; the Census Bureau's 2020-2024 median year built is 1988. Of its 25,557 homes, 1% went up before 1940 and 25% in 2000 or later. Half the homes here are older than that and half newer; yours may sit at either end.
Code and permit facts checked September 10, 2026, rebates October 24, 2026; housing: Census ACS 2020–2024. Sources: stpetersmo.net (2, 3, 4) · ecode360.com (2) · en.wikipedia.org · city-data.com · ameren.com (2, 3, 4) · energystar.gov · data.census.gov. These change; confirm with the building department at 636-477-6600 ext. 1670 or your electric utility first.
Free assessment, a measured R-value, and photos you keep either way.
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