St. Louis City enforces its own energy code edition, which sets its own attic number. Here is that number, whether the work needs a permit, which utility programme pays toward it, and what a house of this vintage usually turns up.
St. Louis City runs to about 62 square miles and roughly 278,144 people. That is roughly 174,694 housing units, and the attic above almost all of them is the cheapest thing in the house left to fix. 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.
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.
Housing of this age in St. Louis City was built before insulation was a line item. The walls are typically empty — brick with a furred-out plaster interior, or balloon-framed timber with cavities that run uninterrupted from the sill all the way to the attic, which is why the top floor of an old house here is cold in a way that no amount of attic fibre fixes on its own. Whatever is in the attic went in later, often over the tops of the joists and often over the top of everything else that had been up there first. We expect open chases behind knee walls, plaster-and-lath ceilings that leak air at every fixture, and balloon cavities that need blocking before anything is blown. Two things we look for before quoting a house this old: loose grey-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.
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.
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. That is the normal state of affairs across this metro — only a handful of the 45 jurisdictions on this site say anything about it 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.
St. Louis City 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.
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.
St. Louis City 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.
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:
Free assessment. We check for vermiculite and knob-and-tube before anything else, and tell you either way.
The code edition St. Louis City 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.
St. Louis City has not published a rule for it. In practice that means one call to the building department before the job starts, which is on us rather than on you.
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 St. Louis City, 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 St. Louis City 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: stlouis-mo.gov · stlouis-mo.gov · stlouis-mo.gov · stlouis-mo.gov · stlouis-mo.gov · insulationinstitute.org · basc.pnnl.gov · stlouis-mo.gov · en.wikipedia.org · censusreporter.org · en.wikipedia.org · stlouis-mo.gov · city-data.com · zip-codes.com · 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.