Insulating a house in Mehlville, without the guesswork: what the county actually publishes on code and permits, what the Department of Energy recommends instead, and which utility programme pays toward the work.
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 13,854 housing units, and the attic above almost all of them is the cheapest thing in the house left to fix. 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-1970s. Postwar building here often meant three or four inches of fibreglass 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.
Housing from this stretch in Mehlville generally got a real attempt at insulation — a real layer in the attic, batts in the walls — so the argument here is rarely about starting from nothing. It is about the gap between what was standard then and what is recommended now, and about the parts nobody insulated at all. Recurring finds: batts stuffed into the rim joist rather than sealed, insulation missing entirely above a cathedral or tray ceiling, soffit vents blocked solid by insulation blown over them with no baffles, and can lights punched straight through the ceiling plane. A house from this era is usually a top-up plus a day of sealing, not a rebuild.
Mehlville does not publish the energy code edition it enforces anywhere we could verify, 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 genuinely 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 and its rules are the ones that apply. The St. Louis County Department of Public Works, Division of Code Enforcement publishes a list of 35 kinds of work that do not require a building permit. Item 35 exempts increasing attic insulation and installing exterior wall insulation under new or replacement siding. The same item states that a building permit is required to install insulation, furring strips and drywall on the room side or the interior basement side of exterior walls. Weatherstripping, caulking and air sealing are not named in the list.
No county publication on contractor licensing could be retrieved.
The published number is 314-615-5184. The department page is here.
Permitting is on us, not on you.
Mehlville is on the Missouri side, which for most addresses means Ameren Missouri — and Ameren Missouri does not hand out a straight per-square-foot insulation rebate the way its Illinois sister utility does. What it runs instead is Pay As You Save: a free home energy assessment, then the work installed by a programme partner and paid back through a fixed monthly charge on the electric bill, which cannot exceed 80% of the estimated monthly saving, so the bill still comes down while it is being repaid. No loan and no credit check.
Published incentives inside that programme for the 2026 programme year are $0.20 per square foot on ceiling and attic insulation, $0.06 per square foot on air sealing, and 50% of costs up to $250 per home on duct sealing. Each one has a condition attached, and they matter:
Ameren Missouri also runs CommunitySavers, which installs attic insulation at no charge for income-eligible households. The program operates through December 31, 2026; incentives are dependent on available funds.
Spire, the gas utility on this side, lists furnace, water heater and thermostat rebates on its Missouri rebate page rather than a standalone insulation one. Its published route to attic insulation and air sealing is the same on-bill Pay As You Save programme, which it co-delivers, plus income-based weatherization. If you are a Spire customer it is worth ringing them to ask what is open this year, because that page moves.
If the household income qualifies, the work can be free rather than discounted. St. Louis County is served by Community Action Agency of St. Louis County (CAASTLC) under the Missouri low-income weatherization program — 314-863-0015, details here.
One more, by its absence: the federal 25C credit, which covered 30% of insulation and air sealing up to $1,200 a year, ended for anything placed in service after 31 December 2025. Work finished on or before that date is still claimed on that year's return; nothing done in 2026 is. It should not be in your 2026 price, whoever tells you otherwise — the rebate guide has the detail.
Mehlville sits in all eight counties are iecc 2021 climate zone 4 on the same map the Department of Energy uses to write its recommendations, which is why the figure it recommends for an attic here is R60 rather than something borrowed from a national advert. Heating and cooling both matter at this latitude. The energy code and rebate guide sets out the numbers behind it.
Elsewhere in St. Louis County we also cover:
Missouri sets none of this at state level, so the number that was right one municipality over is not automatically right here.
| 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 |
| Ellisville | 2015 IRC ch. 11 | R-49 | Not published | 636-227-9660 |
| Eureka | 2018 IRC ch. 11 | R-49 | Not published | 636-938-5233 |
| Florissant | 2021 IECC | R-60 | Not published | 314-839-7648 |
| Kirkwood | 2021 IECC | R-60 | Not published | 314-822-5823 |
| Manchester | Not published | — | Not published | 314-615-5184 |
| Maryland Heights | 2015 IECC | R-49 | Not published | 314-291-6550 |
| Oakville | 2015 IECC | R-49 | Not for an attic top-up | 314-615-5184 |
| Richmond Heights | 2024 IECC | R-49 | Not published | 314-646-7658 |
| Unincorporated St. Louis County | 2015 IECC | R-49 | Not for an attic top-up | 314-615-5184 |
| Town and Country | 2018 IRC ch. 11 | R-49 | Not published | 314-587-2820 |
| University City | 2018 IECC | R-49 | Not published | — |
| Webster Groves | Not published | — | Not published | 314-963-5300 |
| Wildwood | Not published | — | Not for an attic top-up | 636-458-0440 |
Free assessment, a measured R-value, and photos you keep either way.
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 and its rules are the ones that apply. The St. Louis County Department of Public Works, Division of Code Enforcement publishes a list of 35 kinds of work that do not require a building permit. Item 35 exempts increasing attic insulation and installing exterior wall insulation under new or replacement siding. The same item states that a building permit is required to install insulation, furring strips and drywall on the room side or the interior basement side of exterior walls. Weatherstripping, caulking and air sealing are not named in the list.
For most addresses here the route is Ameren Missouri's Pay As You Save programme, which publishes $0.20 per square foot on ceiling and attic insulation and $0.06 per square foot on air sealing for the 2026 programme year. Both carry conditions: the attic has to start at R-20 or below and reach at least R-38, and the air sealing has to cut leakage by at least 20 percent. The incentives sit inside tier 4 of the programme and need you to have lived in the home for the past twelve months, and they are recovered through a monthly charge on the electric bill rather than paid as a cheque. Income-eligible households can get attic insulation at no charge through CommunitySavers instead. The federal 25C credit ended for work placed in service after 31 December 2025.
The typical home in Mehlville dates to around the late-1970s. Postwar building here often meant three or four inches of fibreglass and no attempt at air sealing. If nobody has touched it since, that is what is still up there. That figure is an ACS-derived median republished by housing-data services, not a survey of individual houses.
Not yet. We have no completed job logged in Mehlville, and we would rather say so than put a number on this page that is not real.
Neither state licenses insulation contractors as a trade. In Missouri there is no statewide residential code at all, and registration is imposed city by city — several metro municipalities require a contractor to be registered with them before a permit is pulled. What matters more in practice is utility programme enrolment, because that is what decides whether your rebate is real.
Energy code, permit and department details for Mehlville come from the jurisdiction's own published pages and codified ordinances. Rebate figures come from the utility's own published incentive tables and carry the programme year they were verified in. Housing-age figures are ACS-derived medians republished by housing-data services, so treat them as approximate. Sources: data.mo.gov · library.municode.com · manchestermo.gov · data.mo.gov · dnr.mo.gov · onestl.org · cityofwildwood.com · ecode360.com · ecode360.com · ecode360.com · basc.pnnl.gov · stlouiscountymo.gov · mehlvillefire.com · en.wikipedia.org · bestplaces.net · ameren.com · ameren.com · ameren.com · ameren.com · energy.gov. Adopted code editions, department phone numbers and utility rebate amounts all change — confirm with the jurisdiction or the utility before relying on anything here.