Spray foam insulation in St. Louis, MO: get up to 3 quotes from vetted local installers
Request free quotes from up to three vetted spray foam installers serving St. Louis and nearby St. Louis city. Below: what your climate zone means for open vs closed cell, how much insulation to ask for, Missouri's energy code, and the rebates we could verify.
- Climate zone: 4A (2021 IECC)
- Attic target: R-60 (ENERGY STAR, uninsulated attic)
- State code: No mandatory statewide residential energy code
- Utility rebates we verified: Ameren Missouri Pay As You Save (PAYS)
- Federal 25C credit: ended for 2026 installs
Facts last checked October 16, 2026. Sources are linked in each section.
Where we match quotes from this page
Requests from St. Louis and ZIP codes whose center is within about 20 miles of it go to our St. Louis, MO partner installers (95 ZIP codes): 62024, 62026, 62034, 62040, 62048, 62059, 62060, 62062, 62084, 62087, 62090, 62095, 62201, 62203, 62204, 62205, 62206, 62207, 62208, 62220, 62223, 62226, 62232, 62234, 62236, 62239, 62240, 62260, 62269, 63010, 63011, 63017, 63021, 63026, 63031, 63033, 63034, 63042, 63043, 63044, 63045, 63049, 63052, 63053, 63074, 63088, 63101, 63102, 63103, 63104, 63105, 63106, 63107, 63108, 63109, 63110, 63111, 63112, 63113, 63114, 63115, 63116, 63117, 63118, 63119, 63120, 63121, 63122, 63123, 63124, 63125, 63126, 63127, 63128, 63129, 63130, 63131, 63132, 63133, 63134, 63135, 63136, 63137, 63138, 63139, 63140, 63141, 63143, 63144, 63146, 63147, 63155, 63301, 63303, 63386. Outside these? Send the form anyway and we'll tell you if we can't match you.
Climate zone 4A: what it means for spray foam
St. Louis's central point is in St. Louis city, which the 2021 IECC county map assigns to climate zone 4A (mixed-humid in DOE's Building America terms). Zone 4A is a moist ("A") zone, which drives the vapor and R-value rules below.
Other counties within our St. Louis service radius: Jefferson County (4A), Madison County (4A), Monroe County (4A), St. Charles County (4A), St. Clair County (4A), St. Louis County (4A). All are zone 4A too.
Source: PNNL-33270, Guide to Determining Climate Zone by County (IECC 2021).
Open cell vs closed cell in St. Louis, MO
Attic roofline: both foams are used. The IRC (R806.5) does not require a vapor-retarder coating on open-cell foam under the roof deck in zone 4A (that requirement starts in zone 5), but for hybrid assemblies the foam layer at the deck must be at least R-15 to control condensation. Ask the installer how they manage winter moisture at the roof sheathing.
Closed cell is the usual choice for rim joists, basement and crawlspace walls, where its vapor resistance (about 1.5–2" makes it a Class II vapor retarder) matters most.
How much insulation to ask for
| Where | ENERGY STAR recommendation for zone 4A |
|---|---|
| Attic, uninsulated | R-60 |
| Attic with 3–4" of existing insulation | add R-49 |
| Floor over unconditioned crawlspace/basement | R-19 |
| Basement or crawlspace walls | R-10 continuous or R-13 cavity |
| Exterior walls (when re-siding) | add R-5 to R-10 insulative wall sheathing beneath new siding |
To reach R-60 with foam alone you'd need roughly 16.2–17.1" of open cell (about R-3.5 to R-3.7 per inch) or 8.6–12.0" of closed cell (about R-5 to R-7 per inch). Many roofline spray foam jobs are installed thinner than that and justified through the code's performance path or the unvented-attic rules, so ask every installer to write the foam type, thickness and resulting R-value on the quote and explain how it meets your local code.
Source: ENERGY STAR, Recommended Home Insulation R-Values (based on 2021 IECC). ENERGY STAR's figures are recommendations for existing homes; your local code sets the legal minimum for new work.
Missouri energy code
No mandatory statewide residential energy code. Missouri jurisdictions adopt their own energy codes; NAHB lists St. Louis among the major municipalities that have done so.
Source: NAHB, "Residential Provisions of the IECC: State Adoption Status" (current as of May 2026); official state status at DOE Building Energy Codes Program.
Homes in St. Louis, MO
Census figures for St. Louis city (ACS 2020–2024 5-year estimates): about 174,111 housing units, a median year built of 1938, 86% built before 1980 and 4% built in 2010 or later. 43% are single-family detached homes and 1% are mobile/manufactured homes. 45% of occupied homes are owner-occupied, with a median owner-reported home value of $197,500.
- With 86% of homes built before 1980, many attics here predate modern energy codes. Older attics often need old insulation removed or air-sealed first, and knob-and-tube wiring must be checked before any insulation covers it. Ask whether removal and prep are in the price.
- 67% of homes heat with utility gas. Spray foam makes a house much tighter, which changes how gas furnaces, water heaters and fireplaces draft, so ask whether the installer (or your HVAC contractor) will do combustion safety testing after the job. Some utility rebates require it.
Rebates and incentives for St. Louis, MO
Utility programs that may apply, depending on which utility serves your address:
Ameren Missouri Pay As You Save (PAYS)
Within the PAYS program: $0.20/sq ft for attic insulation (from R-20 or below to at least R-38) and $0.06/sq ft for air sealing with a 20% leakage reduction.
Read on the program's own page October 16, 2026. Programs change; confirm before you sign.
Missouri state Home Energy Rebates
Not yet launched Inflation Reduction Act (IRA) Home Energy Rebates Program
Electrification/appliance rebates (HEAR): "Please note that details about rebate eligibility and how to apply are not finalized at this time. The department cannot provide an estimate as to when rebates will be available to the public. The rebates may not be made available until 2027 at the earliest and potentially as late as 2028."
Whole-home efficiency rebates (HOMES/HER): "Please note that details about rebate eligibility and how to apply are not finalized at this time. The department cannot provide an estimate as to when rebates will be available to the public. The rebates may not be made available until 2027 at the earliest and potentially as late as 2028."
Official source: Missouri Department of Natural Resources. Status text compiled via referencesource.org, last checked by them August 25, 2026. Full Missouri rebate page →
What spray foam costs (national published ranges)
We don't have enough local quotes for St. Louis, MO to publish local prices, and we won't make them up. These national ranges are a starting point; your installers' quotes are what count.
| Example job (typical thickness) | Estimated installed range |
|---|---|
| 1,000 sq ft attic roofline, open cell (6") | $3,600–$9,600 |
| 1,000 sq ft attic roofline, closed cell (3") | $3,900–$9,300 |
| 1,500 sq ft walls, open cell (3.5") | $3,150–$8,400 |
| 1,500 sq ft walls, closed cell (2") | $3,900–$9,300 |
| 200 sq ft rim joists, closed cell (2") | $520–$1,240 |
Board feet × Angi's 2026 installed price per board foot. Angi reports a national average spray foam project of $2,888 (typical $1,455–$4,337). Check a quote you already have →
Questions to ask each installer
- Foam type, brand, thickness and resulting R-value for each area, in writing.
- Which climate zone and code edition they're designing to.
- Whether removal of old insulation, air sealing, and any required ignition/thermal barrier coating are included.
- Whether they participate in Ameren Missouri Pay As You Save (PAYS), and who files the paperwork.
- Whether they'll do (or coordinate) combustion safety testing if you have gas appliances.
FAQ
What climate zone is St. Louis, MO in?
St. Louis city is IECC 2021 climate zone 4A, per PNNL's county list (PNNL-33270).
Should I use open-cell or closed-cell spray foam in St. Louis, MO?
Both work at the roofline in zone 4A; closed cell is the usual pick for rim joists and basement or crawlspace walls. In hybrid roof assemblies the foam layer must be at least R-15.
How much attic insulation do homes in St. Louis, MO need?
ENERGY STAR recommends R-60 for an uninsulated attic in zone 4A (or adding R-49 on top of 3–4 inches of existing insulation). Missouri's code: No mandatory statewide residential energy code.
Are there spray foam or insulation rebates in St. Louis, MO in 2026?
The federal 25C tax credit does not apply to insulation installed after December 31, 2025. Utility programs that may apply, depending on which utility serves your address: Ameren Missouri Pay As You Save (PAYS). Missouri's state Home Energy Rebate program status: Not yet launched.
How much does spray foam cost in St. Louis, MO?
We don't publish local prices until we have enough real local quotes. National published ranges are about $0.60–$1.60 per board foot for open cell and $1.30–$3.10 for closed cell, installed (Angi, 2026), and many companies have a $1,000–$2,000 minimum.
How does requesting quotes work?
Fill in the form once. We pass your request to up to three vetted partner installers who serve St. Louis, MO, and they contact you to schedule an estimate. It's free and there's no obligation.