We cover 3 jurisdictions in Franklin County. Each one below has its own page with the energy code that applies there, the attic R-value it requires, the permit position and the building department's number.
Click a city for its full code, permit and rebate detail.
| City | Energy code | Attic R required | Permit to insulate | Building dept. |
|---|---|---|---|---|
| Pacific | None adopted | — | Not published | 636-271-0500 |
| Union | Not published | — | Not published | 636-583-1805 |
| Washington | Not published | — | Not for an attic top-up | 636-390-1000 |
We name an energy code edition only where the jurisdiction or the state publishes one — 0 of 3 here do. We print a required R-value only where the adopted edition and its local amendments are readable — 0 of 3 here. Everything else is left blank on purpose, and no page on this site fills a blank with a guess.
Missouri has no statewide residential building or energy code. What insulation a house here has to have is decided entirely by whatever code the city, village or county has adopted by local ordinance, and by whether that jurisdiction runs a permit and inspection programme at all. In unincorporated areas the county's code applies; inside a city the municipal ordinance does, and a municipality may contract its permitting back to the county. There is no state floor and no state pre-emption.
That is the whole reason these pages exist. The adopted edition, the R-value behind it and the permit route are all local, and a specification that was correct in the next town over is not automatically correct here.
Franklin County 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.
If the household income qualifies, the work can be free rather than discounted. Franklin County is served by Jefferson-Franklin Community Action Corp. (JFCAC) under the Missouri low-income weatherization program — 636-789-2686, details here. That is a different queue from ours, and we will point you at it rather than sell you something you could get for nothing.
| Figure | Number | What it drives |
|---|---|---|
| Climate zone | All eight counties are IECC 2021 Climate Zone 4 | Every R-value in the code table, on both sides of the river |
| Heating degree days | 4,433 | How hard the furnace works. Base 65°F, 1991–2020 normals at St. Louis Lambert International Airport |
| Cooling degree days | 1,713 | Why an under-insulated attic costs you in July as well as January |
| Nights at or below freezing | 84.9 | Condensation on the cold side of the insulation |
| Days that never rise above freezing | 19.3 | Most St. Louis freezes thaw the same day — the cycling is the problem, not the cold |
The full explanation is in our St. Louis energy code and rebate guide.
Free assessment, a measured R-value, and photos you keep either way.