Insulation and air sealing for Festus homes: attics, crawl spaces, rim joists and walls, starting with a free assessment of the R-value you actually have. The typical home here dates to the early-1980s, and 9% of its 5,539 homes went up before 1940.
Festus runs to about 5.9 square miles and roughly 12,706 people. It sits about 30 miles south of downtown St. Louis. Around 5,539 housing units sit inside those boundaries. The community dates back to 1887. We cover ZIP code 63028.
No completed job in Festus is logged in our records yet, and this page will say so until one is.
The typical home in Festus dates to around the early-1980s. Houses of this vintage usually got batts or blown fiber at whatever the standard of the day was, which is well short of what is recommended now. Most are one top-up away from being right.
, pointing to a housing stock built mostly from the 1980s-90s, with an older minority predating 1950.
Festus grew as an outgrowth of neighboring Crystal City and was originally called "Tanglefoot," then "Limitville," before taking the name Festus; it was established in 1878 and incorporated in 1887.
The Census Bureau estimates 5,539 homes in Festus. 471 of them (9%) went up before 1940 — 16th of 44 places on this site for pre-1940 housing. The 2000s were the busiest decade, adding 1,018 of today's homes (18%); 47% predate 1980 and 31% were built in 2000 or later. For Jefferson County as a whole the pre-1940 share is 3%, so Festus sits above it.
Of 5,091 occupied homes, 50% heat with utility gas and 49% with electricity. Electric heat here is less common than across the county (58%), and ranks 6th of 44 on this site. That is why the assessment asks how the house is heated: the fuel and the name on the utility bill decide which program, if any, can pay toward the work.
58% of occupied homes are owner-occupied and 73% of all homes are single-family detached houses, with 265 mobile homes in the count. Read together, those numbers point toward air sealing on newer houses that already have depth and an energy assessment before deciding what to fix first.
| Built | Homes | Share | |
|---|---|---|---|
| Before 1940 | 471 | 9% | |
| 1940s | 374 | 7% | |
| 1950s | 871 | 16% | |
| 1960s | 556 | 10% | |
| 1970s | 355 | 6% | |
| 1980s | 455 | 8% | |
| 1990s | 756 | 14% | |
| 2000s | 1,018 | 18% | |
| 2010s | 467 | 8% | |
| 2020 or later | 216 | 4% |
5,539 homes, Census ACS 2020–2024 (B25034, B25040, B25003); 5,091 occupied.
1,211 of Festus' 5,539 homes (22%) were built in the 1980s and 1990s. The gaps in houses of that age are the parts nobody sealed: batts stuffed into the rim joist, bare spots over cathedral and tray ceilings, soffit vents buried with no baffles, can lights punched through the ceiling plane. A top-up plus a day of sealing usually covers it.
Festus does not publish the energy code edition it enforces, so this page does not name one. Section 500.010(A) of the Festus code, Ord. No. 4785 of 8-26-2024, adopts the 2021 International Building Code, 2021 International Residential Code, 2021 International Fire Code, 2021 International Fuel Gas Code, 2021 International Mechanical Code, 2021 International Plumbing Code, 2020 National Electrical Code, 2021 International Property Maintenance Code, 2021 International Swimming Pool and Spa Code and 2021 International Private Sewage Disposal Code. The ordinance does not name the International Energy Conservation Code. The article makes no mention of energy, Chapter 11, N1101, N1102, insulation or the IECC, so nothing in the ordinance either adopts an IECC edition or deletes Chapter 11 of the adopted 2021 IRC. 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 wide spread. Ask which one your contractor is building to.
Nothing Festus publishes settles this. Its permit lists name the work types it cares about, and insulation is not among them in either direction. The residential building permit page states that any project involving the replacement or installation of framing, plumbing or electrical requires a permit. Insulation, weatherization and air sealing are not listed as permit work types, and the code's permit exemption in Section 500.015 names only fencing not over 7 feet in height. So we ask the department directly before the first day on site, and whatever comes back, pulling it is our job rather than yours.
The published number is 636-937-6646. The department page is here.
Permitting is on us, not on you.
Most Festus 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. 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 Jefferson-Franklin Community Action Corp. (JFCAC) (636-789-2686) for free weatherization instead. The full program rules are on the Jefferson County page and in the rebate guide.
Every layer of an insulated attic, explained
Elsewhere in Jefferson County we also cover:
Also on this site, in neighboring St. Louis County:
Missouri sets none of this at state level. Across the 3 places in this table there are 2 different adopted editions (2015 IECC and 2021 IECC), and none of the 3 publishes a permit rule for insulation.
| City | Energy code | Attic R required | Permit to insulate | Building dept. |
|---|---|---|---|---|
| Festus | Not published | — | Not published | 636-937-6646 |
| Arnold | 2021 IECC | — | Not published | 636-282-2378 |
| Imperial | 2015 IECC | R-49 | Not published | 636-797-5555 |
All 3 Jefferson County jurisdictions side by side →
Festus 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.
Not on paper: Festus names neither a permit nor an exemption for insulation, so one call to the department at 636-937-6646 settles it first.
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 Festus dates to around the early-1980s; the Census Bureau's 2020-2024 median year built is 1983. Of its 5,539 homes, 9% went up before 1940 and 31% 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 · festusmo.gov (2, 3, 4) · en.wikipedia.org · bestplaces.net · ameren.com (2, 3, 4) · energystar.gov · data.census.gov. These change; confirm with the building department at 636-937-6646 or your electric utility first.
Free assessment, a measured R-value, and photos you keep either way.
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