Insulation and air sealing for St. Louis City homes: attics, crawl spaces, rim joists and walls, starting with a free assessment of the R-value you actually have. St. Louis City enforces the 2018 IECC, which sets R-49 for a new attic.
St. Louis City runs to about 62 square miles and roughly 278,144 people. That is roughly 174,111 housing units. The community dates back to 1764. We cover the 631xx ZIP codes across the city.
Our job history shows nothing in St. Louis City so far. Plenty of sites will show you a number here anyway.
The typical home in St. Louis City dates to around the 1930s or earlier. Houses built before the war generally went up with nothing in the walls at all and whatever went into the attic afterwards. Anything up there was added later, usually in a hurry.
More than half of the city's housing was built 1939 or earlier — St. Louis's housing stock is dominated by early-20th-century brick two- and four-family flats and rowhouses, not a later suburban build-out.
We work across St. Louis City rather than one corner of it — Downtown, Midtown, The Hill, Soulard, Tower Grove South, Central West End, Lafayette Square, Forest Park Southeast, Shaw and Lindenwood Park included. Construction and vintage change between them, sometimes by thirty years and a whole different framing method, which decides whether a wall can be dense-packed at all.
The city has a Cultural Resources Office/Preservation Board that administers 18 local historic districts (10 regular, 8 certified); population decline since the 1950 peak has left a significant stock of abandoned residential buildings and vacant lots.
The Census Bureau estimates 174,111 homes in St. Louis City. 100,811 of them (58%) went up before 1940 — the highest share of pre-1940 housing among the 44 places on this site. More of today's homes date from before 1940 than from any single decade since, and 86% predate 1980.
Of 144,891 occupied homes, 67% heat with utility gas and 31% with electricity. Whoever comes out will ask about the furnace or heat pump first, since the heating fuel and the utility named on the bill settle which program money is on the table.
45% of occupied homes are owner-occupied and 43% of all homes are single-family detached houses, with 840 mobile homes in the count. Read together, those numbers point toward wall insulation for walls built empty, a vermiculite check before anything is disturbed and an energy assessment before deciding what to fix first.
| Built | Homes | Share | |
|---|---|---|---|
| Before 1940 | 100,811 | 58% | |
| 1940s | 12,735 | 7% | |
| 1950s | 17,877 | 10% | |
| 1960s | 11,137 | 6% | |
| 1970s | 7,526 | 4% | |
| 1980s | 5,851 | 3% | |
| 1990s | 4,730 | 3% | |
| 2000s | 7,004 | 4% | |
| 2010s | 5,690 | 3% | |
| 2020 or later | 750 | 0% |
174,111 homes, Census ACS 2020–2024 (B25034, B25040, B25003); 144,891 occupied.
113,546 of St. Louis City's 174,111 homes (65%) went up before 1950. In houses that old the air leaves before any insulation can slow it: balloon-framed bays open from the sill to the attic, open chases behind knee walls, plaster-and-lath ceilings leaking at every fixture. Those get blocked and sealed first. Two checks come before any quote on a house this old: loose gray-brown flakes in the attic, and cloth-covered wiring on ceramic knobs.
St. Louis City enforces the 2018 IECC. The Building Division's table of adopted codes lists the 2018 International Energy Conservation Code, adopted by Ordinance 70799, effective August 1, 2018. The same table shows the 2018 International Building Code (Ordinance 70794), the 2018 International Residential Code (Ordinance 70795) and the 2018 International Existing Building Code (Ordinance 70797), all effective the same day.
That edition sets R-49 for the attic in new work, and R-20, or R-13 cavity 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.
2018 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. The North American Insulation Manufacturers Association's Missouri energy code sheet states the same values for St. Louis: ceiling R-49 or U-0.026, walls R-20 or R-13+5 continuous or U-0.057.
There is no published answer for St. Louis City. Neither the permit-required list nor the exemption list mentions insulation or air sealing at all. The city's page 'When a Residential Building Permit is Needed' gives both a list of work that requires a permit and a list of work that does not. Insulation, attic insulation, air sealing and weatherization appear in neither list. The exempt list includes 'ordinary repairs to residential buildings and structures up to four (4) units,' tuckpointing, plaster patching, painting, floor sanding and window and door replacement in existing openings. That silence is not permission and it is not a prohibition. We settle it with a phone call before the crew is scheduled.
The published number is 314-622-3313. The department page is here.
Permitting is on us, not on you.
Most St. Louis City 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. The conditions: an attic going from R-20 or below to at least R-38, air sealing that cuts measured leakage by 20 percent, and twelve months in the home. CommunitySavers can include attic insulation at no charge for income-eligible households. The full program rules are in the rebate guide.
Every layer of an insulated attic, explained
St. Louis City borders St. Louis County and East St. Louis, Illinois (across the Mississippi River). These are the ones we also cover, each with its own energy code and permit rule:
Also on this site, in neighboring St. Louis County:
Missouri sets none of this at state level. Across the 2 places in this table there are 2 different adopted editions (2015 IECC and 2018 IECC), and one of the two publishes a permit rule for insulation.
| City | Energy code | Attic R required | Permit to insulate | Building dept. |
|---|---|---|---|---|
| St. Louis City | 2018 IECC | R-49 | Not published | 314-622-3313 |
| Unincorporated St. Louis County | 2015 IECC | R-49 | Not for an attic top-up | 314-615-5184 |
St. Louis City enforces the 2018 IECC, which sets R-49 for an attic in new work. Whether it reaches a retrofit of an existing house is not published.
St. Louis City has not published a rule for it; the building department at 314-622-3313 is called before the job starts.
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 St. Louis City dates to around the 1930s or earlier; the Census Bureau's 2020-2024 median year built is 1939 or earlier. Of its 174,111 homes, 58% went up before 1940 and 8% 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: stlouis-mo.gov (2, 3, 4, 5, 6, 7) · insulationinstitute.org · basc.pnnl.gov · en.wikipedia.org (2) · censusreporter.org · city-data.com · zip-codes.com · ameren.com (2, 3, 4) · energystar.gov · data.census.gov. These change; confirm with the building department at 314-622-3313 or your electric utility first.
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