Attic insulation, air sealing, crawl spaces and walls for homes in Union — starting with a free assessment that measures the R-value you actually have. The typical home here dates to the mid-1990s, and 8% of its 5,399 homes went up before 1940.
Union runs to about 9.0 square miles and roughly 12,348 people. It sits about 50 miles southwest of downtown St. Louis. That is roughly 5,399 housing units. The community dates back to 1826. We cover ZIP code 63084.
Our job history shows nothing in Union so far. Plenty of sites will show you a number here anyway.
The typical home in Union dates to around the mid-1990s. 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.
, consistent with the city's fastest population-growth period of 2000-2010 — housing skews toward 1990s-2000s suburban construction.
Union is the Franklin County seat (designated 1827), sited on the Bourbeuse River; population grew from 402 in 1880 to 12,348 by 2020.
The Census Bureau estimates 5,399 homes in Union. 432 of them (8%) went up before 1940 — 17th of 44 places on this site for pre-1940 housing. The 2000s were the busiest decade, adding 1,379 of today's homes (26%); 31% predate 1980 and 44% were built in 2000 or later. For Franklin County as a whole the pre-1940 share is 10%, so Union sits below it.
Of 4,990 occupied homes, 10% heat with utility gas and 85% with electricity; another 2% burn propane or other tank gas. Electric heat here is more common than across the county (68%), and ranks 1st of 44 on this site. Which utility program can contribute depends on the heating fuel and on who sends the bill, so that is the first thing an assessment pins down.
61% of occupied homes are owner-occupied and 64% of all homes are single-family detached houses, with 414 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 | 432 | 8% | |
| 1940s | 185 | 3% | |
| 1950s | 318 | 6% | |
| 1960s | 401 | 7% | |
| 1970s | 314 | 6% | |
| 1980s | 517 | 10% | |
| 1990s | 848 | 16% | |
| 2000s | 1,379 | 26% | |
| 2010s | 888 | 16% | |
| 2020 or later | 117 | 2% |
5,399 homes, Census ACS 2020–2024 (B25034, B25040, B25003); 4,990 occupied.
1,365 of Union's 5,399 homes (25%) 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.
Union does not publish the energy code edition it enforces, so this page does not name one. Chapter 500, Article I of the City of Union code adopts the 2021 International Building Code in Section 500.010(A) by Ordinance No. 4630 of 11-13-2023, the 2021 International Existing Building Code in Section 500.055(A) by Ordinance No. 4631 of 11-13-2023, and the 2021 International Residential Code in Section 500.060(A) by Ordinance No. 4636 of 11-13-2023, along with the 2020 NEC and 2021 plumbing, mechanical and fuel gas codes. Section 500.065(A)(49) deletes Chapter 11 Energy Efficiency from the adopted IRC, and the city also deletes IBC Section 101.4.6 Energy. No article adopting any edition of the International Energy Conservation Code exists in the codified chapter. The city's own Building Codes web page does list an International Energy Conservation Code among its 2021 codes, which the codified ordinance does not show; this page follows the ordinance, and the difference is worth one call to the building and engineering counter before a job is priced. 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.
There is no published answer for Union. Neither the permit-required list nor the exemption list mentions insulation or air sealing at all. Union deleted items 1 and 2 of the IBC Section 105.2 permit exemption list, and the permits page says only that the department reviews plans and issues building permits for all residential and commercial construction and remodeling projects. Insulation, weatherization and air sealing are not named on either the permit list or the 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.
No contractor licensing or registration provision appears in Chapter 500 Article I, and the city's permits page does not mention one.
The published number is 636-583-1805. The department page is here.
Permitting is on us, not on you.
Most Union 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 Franklin County page and in the rebate guide.
Every layer of an insulated attic, explained
Elsewhere in Franklin 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 none of them publishes an energy code edition, and 1 of the 3 publishes a permit rule for insulation.
| City | Energy code | Attic R required | Permit to insulate | Building dept. |
|---|---|---|---|---|
| Union | Not published | — | Not published | 636-583-1805 |
| Pacific | None adopted | — | Not published | 636-271-0500 |
| Washington | Not published | — | Not for an attic top-up | 636-390-1000 |
All 3 Franklin County jurisdictions side by side →
Union 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.
Union has not published a rule for it; the building department at 636-583-1805 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 Union dates to around the mid-1990s; the Census Bureau's 2020-2024 median year built is 1996. Of its 5,399 homes, 8% went up before 1940 and 44% in 2000 or later. Half the homes here are older than that and half newer; yours may sit at either end.
Code and permit facts checked September 10, 2026, rebates October 24, 2026; housing: Census ACS 2020–2024. Sources: ecode360.com · unionmissouri.gov (2) · cms4files.revize.com · en.wikipedia.org · city-data.com · ameren.com (2, 3, 4) · energystar.gov · data.census.gov. These change; confirm with the building department at 636-583-1805 or your electric utility first.
Free assessment, a measured R-value, and photos you keep either way.
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