Insulation and air sealing for Affton homes: attics, crawl spaces, rim joists and walls, starting with a free assessment of the R-value you actually have. Affton enforces the 2015 IECC, which sets R-49 for a new attic.
Affton runs to about 4.6 square miles and roughly 19,052 people. It sits about 8 miles south of downtown St. Louis. That is roughly 9,092 housing units. We cover ZIP codes 63123 and 63125.
Our job history shows nothing in Affton so far. Plenty of sites will show you a number here anyway.
The typical home in Affton dates to around the late-1950s. Postwar building here often meant three or four inches of fiberglass and no attempt at air sealing. If nobody has touched it since, that is what is still up there.
Largely postwar, with the single largest decade of construction in the 1950s (about 31% of homes).
Affton is an unincorporated CDP named for postmaster Johann Aff; its median housing construction year is 1958, reflecting a classic postwar St. Louis County inner suburb.
The Census Bureau estimates 9,092 homes in Affton. 776 of them (9%) went up before 1940 — 15th of 44 places on this site for pre-1940 housing. The 1950s were the busiest decade, adding 2,820 of today's homes (31%); 83% predate 1980 and 5% were built in 2000 or later. For St. Louis County as a whole the pre-1940 share is 10%, so Affton sits below it.
Of 8,695 occupied homes, 81% heat with utility gas and 16% with electricity; another 2% burn propane or other tank gas. Electric heat here is less common than across the county (23%), and ranks 41st 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.
81% of occupied homes are owner-occupied and 83% of all homes are single-family detached houses. Read together, those numbers point toward an attic top-up over postwar fiberglass.
| Built | Homes | Share | |
|---|---|---|---|
| Before 1940 | 776 | 9% | |
| 1940s | 1,377 | 15% | |
| 1950s | 2,820 | 31% | |
| 1960s | 1,863 | 20% | |
| 1970s | 733 | 8% | |
| 1980s | 439 | 5% | |
| 1990s | 588 | 6% | |
| 2000s | 218 | 2% | |
| 2010s | 251 | 3% | |
| 2020 or later | 27 | 0% |
9,092 homes, Census ACS 2020–2024 (B25034, B25040, B25003); 8,695 occupied.
5,416 of Affton's 9,092 homes (60%) date from 1950 through 1979. The leaks in houses of that era repeat: nothing over the top plates, wire and pipe holes left open, an unsealed hatch, a bath fan venting into the attic, and in ranches and split-levels, heat lost at the garage ceiling and over cantilevered floors. Sealing the plates, holes and fans comes before any more fiber, and it is usually a day's work, not a renovation.
Affton enforces the 2015 IECC. Affton is unincorporated St. Louis County, so permitting and code enforcement are the county's, not a city's. The Missouri state building code database published at data.mo.gov lists Affton with a 2015 IECC energy code, the 2015 IRC and the 2015 IBC.
That edition sets R-49 for the attic in new work, and R-20, or R-13 plus R-5 continuous for walls. The Department of Energy's recommendation for this climate zone runs higher: R60 for an attic with nothing in it, R49 where a few inches are already down.
Table R402.1.2 of the 2015 IECC, climate zone 4 except marine, per the U.S. Department of Energy's 'Residential Provisions of the 2015 International Energy Conservation Code' (ceiling 49; wood frame wall 20 or 13+5).
This is unincorporated St. Louis County, so the county's Division of Code Enforcement is the permit desk here. Item 35 of its no-permit list exempts increasing attic insulation and adding exterior wall insulation under new siding, but insulating the room side of an exterior wall needs a building permit.
The county's full no-permit list, and what it says about walls and basements, is set out on the unincorporated St. Louis County page.
The published number is 314-615-5184. The department page is here.
Permitting is on us, not on you.
Affton 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. 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 Community Action Agency of St. Louis County (CAASTLC) (314-863-0015) for free weatherization instead. The St. Louis County page and the rebate guide carry the full rules.
Every layer of an insulated attic, explained
Elsewhere in St. Louis County we also cover:
Missouri sets none of this at state level. Across the 7 places in this table there are 4 different adopted editions (2015 IECC, 2018 IRC ch. 11, 2021 IECC and 2024 IECC), and 1 of the 7 publishes a permit rule for insulation.
| City | Energy code | Attic R required | Permit to insulate | Building dept. |
|---|---|---|---|---|
| Affton | 2015 IECC | R-49 | Not for an attic top-up | 314-615-5184 |
| Ballwin | Not published | — | Not published | 636-227-2129 |
| Brentwood | 2024 IECC | R-49 | Not published | 314-963-8602 |
| Chesterfield | Not published | — | Not published | 636-537-4000 |
| Clayton | 2021 IECC | R-60 | Not published | 314-290-8463 |
| Creve Coeur | 2015 IECC | R-49 | Not published | 314-872-2500 |
| Des Peres | 2018 IRC ch. 11 | R-49 | Not published | 314-835-6130 |
All 21 St. Louis County jurisdictions side by side →
Affton enforces the 2015 IECC, which sets R-49 for an attic in new work. Whether it reaches a retrofit of an existing house is not published.
This is unincorporated St. Louis County, so the county's Division of Code Enforcement is the permit desk here. Item 35 of its no-permit list exempts increasing attic insulation and adding exterior wall insulation under new siding, but insulating the room side of an exterior wall needs a building permit.
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 Affton dates to around the late-1950s; the Census Bureau's 2020-2024 median year built is 1958. Of its 9,092 homes, 9% went up before 1940 and 5% 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: data.mo.gov (2) · library.municode.com · manchestermo.gov · energycodes.gov · dnr.mo.gov · onestl.org · cityofwildwood.com · ecode360.com (2, 3) · basc.pnnl.gov · stlouiscountymo.gov · en.wikipedia.org · censusreporter.org · point2homes.com · ameren.com (2, 3, 4) · energystar.gov · data.census.gov. These change; confirm with the building department at 314-615-5184 or your electric utility first.
Free assessment, measured at the hatch, with the photographs and the number in writing.
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