Insulation and air sealing for Florissant homes: attics, crawl spaces, rim joists and walls, starting with a free assessment of the R-value you actually have. Florissant enforces the 2021 IECC, which sets R-60 for a new attic.
Florissant runs to about 13 square miles and roughly 52,533 people. It sits about 14 miles north of downtown St. Louis. That is roughly 23,064 housing units. The community dates back to 1785. We cover ZIP codes 63031, 63032, 63033 and 63034.
Our job history shows nothing in Florissant so far. Plenty of sites will show you a number here anyway.
The typical home in Florissant dates to around the early-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.
Around 18,000 houses were built in Florissant between 1947 and 1980 as the city's population surged toward a mid-1970s peak near 76,000 -- making its housing stock overwhelmingly postwar/mid-century, aside from the older Old Town core.
That includes Old Town. Housing age and construction shift across Florissant, sometimes by decades within a few streets, which is why we look in the attic before quoting rather than after.
Florissant has a city Landmarks and Historic Districts Commission and a large historic core (Old Town / St. Ferdinand) with properties dating to the 1790s, surrounded by a huge ring of 1947-1980 postwar housing.
The Census Bureau estimates 23,064 homes in Florissant. 403 of them (2%) went up before 1940 — 29th of 44 places on this site for pre-1940 housing. The 1960s were the busiest decade, adding 8,874 of today's homes (38%); 90% predate 1980 and 3% were built in 2000 or later. For St. Louis County as a whole the pre-1940 share is 10%, so Florissant sits below it.
Of 21,229 occupied homes, 83% heat with utility gas and 15% with electricity. Electric heat here is less common than across the county (23%), and ranks 42nd of 44 on this site. 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.
67% of occupied homes are owner-occupied and 79% 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.
| Built | Homes | Share | |
|---|---|---|---|
| Before 1940 | 403 | 2% | |
| 1940s | 908 | 4% | |
| 1950s | 7,443 | 32% | |
| 1960s | 8,874 | 38% | |
| 1970s | 3,024 | 13% | |
| 1980s | 1,411 | 6% | |
| 1990s | 413 | 2% | |
| 2000s | 468 | 2% | |
| 2010s | 99 | 0% | |
| 2020 or later | 21 | 0% |
23,064 homes, Census ACS 2020–2024 (B25034, B25040, B25003); 21,229 occupied.
19,341 of Florissant's 23,064 homes (84%) 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.
Florissant enforces the 2021 IECC. Chapter 500, Article IX, Section 500.220 of the Florissant city code adopts the International Energy Conservation Code, 2021 Edition, as published by the International Code Council, by Ordinance No. 8748 dated November 22, 2021, which repealed and replaced the city's former Chapter 500. The same ordinance adopted the rest of the 2021 code family, including the building, residential, mechanical, plumbing, fire, fuel gas, swimming pool and spa, private sewage disposal, property maintenance and existing building codes. The listed local amendments name the Planning and Zoning Commission as the board of appeals, set penalties under Section 100.080, delete Sections C106 and R106 (Notice of Approval), and add electric-vehicle-ready parking requirements for commercial and multi-family projects.
That edition sets R-60 for the attic in new work, and R-30, or R-20 cavity plus R-5 continuous, or R-13 cavity plus R-10 continuous, or R-20 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.
2021 IECC Table R402.1.3, 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.
There is no published answer for Florissant. Neither the permit-required list nor the exemption list mentions insulation or air sealing at all. The city's permits page lists construction permits for plumbing, electrical, mechanical and building work, container permits, occupancy inspections and certificates, rental licenses, excavation permits, contractor bonding and insurance filings and business licenses. Insulation, air sealing and weatherization are not named, and the city publishes no exemption list. That silence is not permission and it is not a prohibition. We settle it with a phone call before the crew is scheduled.
The permits page shows contractor bonding and insurance filings handled by the Engineering Department and business licenses handled by the Finance Department, but it does not state that a contractor, or an insulation contractor specifically, must register with the city before doing work.
The published number is 314-839-7648. The department page is here.
Permitting is on us, not on you.
Florissant is on the Missouri side, where most addresses buy their electricity from Ameren Missouri. Its Pay As You Save program publishes $0.20 per square foot on ceiling and attic insulation and $0.06 per square foot on air sealing for the 2026 program year; the incentive comes off the cost and the rest is repaid through a monthly charge on the 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 St. Louis County page and the rebate guide carry the full rules.
Every layer of an insulated attic, explained
Florissant borders Hazelwood, Ferguson, Black Jack and Old Jamestown.
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 1 of the 7 publishes a permit rule for insulation.
| City | Energy code | Attic R required | Permit to insulate | Building dept. |
|---|---|---|---|---|
| Florissant | 2021 IECC | R-60 | Not published | 314-839-7648 |
| 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 →
Florissant enforces the 2021 IECC, which sets R-60 for an attic in new work. Whether it reaches a retrofit of an existing house is not published.
Florissant has not published a rule for it; the building department at 314-839-7648 is called before the job starts.
Ameren Missouri's Pay As You Save: $0.20 per square foot for an attic starting at R-20 or below and $0.06 per square foot for air sealing in 2026, with the balance on the electric bill. The federal 25C credit ended for work placed in service after December 31, 2025.
The typical home in Florissant dates to around the early-1960s; the Census Bureau's 2020-2024 median year built is 1963. Of its 23,064 homes, 2% went up before 1940 and 3% 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: ecode360.com (2, 3) · florissantmo.com (2, 3) · basc.pnnl.gov · en.wikipedia.org · bestplaces.net · ameren.com (2, 3, 4) · energystar.gov · data.census.gov. These change; confirm with the building department at 314-839-7648 or your electric utility first.
Free assessment, measured at the hatch, with the photographs and the number in writing.
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