Insulation and air sealing for Mehlville homes: attics, crawl spaces, rim joists and walls, starting with a free assessment of the R-value you actually have. The typical home here dates to the late-1960s, and 1% of its 13,994 homes went up before 1940.
Mehlville runs to about 7.6 square miles and roughly 28,955 people. It sits about 12 miles south of downtown St. Louis. That is roughly 13,994 housing units. We cover ZIP codes 63125, 63128 and 63129.
Our job history shows nothing in Mehlville so far. Plenty of sites will show you a number here anyway.
The typical home in Mehlville dates to around the late-1960s. 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.
, consistent with Mehlville's description in census data as a fully urbanized, inner-ring St. Louis County suburb.
Mehlville is an unincorporated census-designated place -- never a city -- and is 100% urban per census data, encompassing areas also associated with the Lemay, Tesson Ferry, and Oakville townships.
The Census Bureau estimates 13,994 homes in Mehlville. 186 of them (1%) went up before 1940 — 36th of 44 places on this site for pre-1940 housing. The 1960s were the busiest decade, adding 4,236 of today's homes (30%); 71% predate 1980 and 8% were built in 2000 or later. For St. Louis County as a whole the pre-1940 share is 10%, so Mehlville sits below it.
Of 13,507 occupied homes, 60% heat with utility gas and 37% with electricity; another 2% burn propane or other tank gas. Electric heat here is more common than across the county (23%), and ranks 14th 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.
66% of occupied homes are owner-occupied and 59% of all homes are single-family detached houses. With houses like these, the conversations we expect most are about an attic top-up over postwar fiberglass and an energy assessment before deciding what to fix first.
| Built | Homes | Share | |
|---|---|---|---|
| Before 1940 | 186 | 1% | |
| 1940s | 630 | 5% | |
| 1950s | 2,278 | 16% | |
| 1960s | 4,236 | 30% | |
| 1970s | 2,569 | 18% | |
| 1980s | 1,786 | 13% | |
| 1990s | 1,166 | 8% | |
| 2000s | 552 | 4% | |
| 2010s | 580 | 4% | |
| 2020 or later | 11 | 0% |
13,994 homes, Census ACS 2020–2024 (B25034, B25040, B25003); 13,507 occupied.
9,083 of Mehlville's 13,994 homes (65%) 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.
Mehlville does not publish the energy code edition it enforces, so this page does not name one. Mehlville is unincorporated St. Louis County, so permitting and code enforcement are the county's, not a city's. The Missouri state building code database at data.mo.gov has a Mehlville row but no energy, residential or commercial code entry in it; the same database lists the 2015 IECC, 2015 IRC and 2015 IBC for the neighboring unincorporated communities of Affton and Oakville, which are governed by the same county code. Across this metro the adopted editions run from the 2015 IECC to the 2024 IECC, and several jurisdictions have no energy code at all, which is a wide spread. Ask which one your contractor is building to.
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.
Most Mehlville 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 Community Action Agency of St. Louis County (CAASTLC) (314-863-0015) for free weatherization instead. The full program rules are on the St. Louis County page and in the rebate guide.
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 3 different adopted editions (2015 IECC, 2021 IECC and 2024 IECC), and 2 of the 7 publish a permit rule for insulation.
| City | Energy code | Attic R required | Permit to insulate | Building dept. |
|---|---|---|---|---|
| Mehlville | Not published | — | Not for an attic top-up | 314-615-5184 |
| 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 |
All 21 St. Louis County jurisdictions side by side →
Mehlville does not publish the energy code edition it enforces, so we do not state a required figure here. The Department of Energy recommends R60 for an uninsulated attic in this climate zone and R49 where there are already a few inches.
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.
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 Mehlville dates to around the late-1960s; the Census Bureau's 2020-2024 median year built is 1969. Of its 13,994 homes, 1% went up before 1940 and 8% in 2000 or later. That is a median across the whole place, so your own house may be older or newer.
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 · dnr.mo.gov · onestl.org · cityofwildwood.com · ecode360.com (2, 3) · basc.pnnl.gov · stlouiscountymo.gov · mehlvillefire.com · en.wikipedia.org · bestplaces.net · 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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