What it actually takes to insulate a house in Unincorporated St. Louis County — what the county publishes about energy code and permits, what it does not, the rebate your address qualifies for, and how old the housing here really is.
This page covers the parts of the county that are not inside a city — where the county, not a municipality, runs building and permits. The Census does not publish population or housing totals for that remainder on its own, so this page does not quote any: the figures you will see elsewhere for “St. Louis County” include every municipality in it as well.
We have not logged a completed job in Unincorporated St. Louis County yet. We would rather say so than put a number on this page that is not real.
The county's Historic Buildings Commission maintains a countywide National Register list, but districts are attributed to specific municipalities rather than the unincorporated area as a whole.
Unincorporated St. Louis County enforces the 2015 IECC. The State of Missouri's building-codes-by-county dataset on the Missouri Data Portal, which the Department of Natural Resources points to as the state's energy-code-by-jurisdiction source, lists St. Louis County as 2015 IECC, 2015 IRC and 2015 IBC. OneSTL, the regional plan site run by East-West Gateway Council of Governments, also states that St. Louis County adopted the 2015 IECC. The county's building code chapter is Chapter 1115 SLCRO and its residential code is Chapter 1116 SLCRO; both were most recently reissued by County Ordinance 27,654, approved December 18, 2019 and effective April 1, 2020, as confirmed by the cities of Berkeley, Breckenridge Hills and Wildwood, which adopt those county chapters by reference.
Under that edition the required attic value for new work here is R-49, and walls R-20, or R-13 cavity plus R-5 continuous. For comparison, the Department of Energy recommends R60 for an uninsulated attic in this climate zone and R49 where there are already a few inches up there.
2015 IECC Table R402.1.2, climate zone 4 (except marine), as reproduced in the U.S. Department of Energy / PNNL Building America Solution Center comparison of 2009-2021 IECC and IRC minimum insulation requirements. These values follow from the 2015 IECC edition the state dataset attributes to the county.
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.
St. Louis County licenses electrical, plumbing and mechanical contractors, and municipalities in the county require those trades to hold a current county license: Ballwin requires permit-pulling electrical, plumbing and mechanical contractors to hold an active St. Louis County license in their field, and University City issues electrical permits only to contractors licensed by St. Louis County.
The published number is 314-615-5184. The department page is here.
Permitting is on us, not on you.
Unincorporated St. Louis County 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.
Unincorporated St. Louis County sits in all eight counties are iecc 2021 climate zone 4, mixed-humid, which is the zone that has to be defended in both directions: 4,433 heating degree days and 1,713 cooling degree days a year at Lambert. That is what every R-value on this page is sized for. The energy code and rebate guide works through the rest of the figures.
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 |
| Mehlville | Not published | — | Not for an attic top-up | 314-615-5184 |
| 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 |
| 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.
The code edition Unincorporated St. Louis County enforces sets R-49 for new work. The Department of Energy separately recommends R60 for an uninsulated attic in this climate zone, and R49 where a few inches are already there.
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.
Not yet. We have no completed job logged in Unincorporated St. Louis County, 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 Unincorporated St. Louis County 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 · dnr.mo.gov · onestl.org · cityofwildwood.com · ecode360.com · ecode360.com · ecode360.com · basc.pnnl.gov · manchestermo.gov · stlouiscountymo.gov · stlouiscountymo.gov · en.wikipedia.org · censusreporter.org · stlouiscountymo.gov · 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.