Air sealing for St. Louis homes, done before insulation: top plates, chases, the attic hatch and rim joists. For climate zone 4, EPA estimates sealing and insulating a typical home cuts heating and cooling costs about 17 percent.
Air sealing closes the holes between the living space and the attic, crawl space and basement: top plates where walls meet the attic floor, wire and pipe holes, chases, dropped soffits, the attic hatch, and the rim joist where the frame sits on the foundation. EPA's ENERGY STAR program sets the order plainly, sealing first and insulation second, and its sealing guide says even a well-insulated attic performs better once the leaks under it are closed.
We seal before any insulation goes in, and where the job calls for one, a blower door goes on the house before and after so the reduction is measured. Below: what moves the price, what each Ameren utility pays for in 2026 and on what terms, where St. Louis houses leak, and what to know before you make a house tighter.
There is no flat price, because two houses of the same size can have very different numbers of openings. The proposal lists each area to be sealed, and the price moves with how many top plates, penetrations, chases and soffits are open, how much insulation has to be pulled back and replaced to reach them, how easy the attic and rim joist are to get at, and whether a blower door test is needed at both ends.
What the utilities pay toward it in 2026:
Leave the federal 25C credit out of any 2026 math; it covers nothing placed in service after 2025.
Because the biggest leaks are usually not at the windows. EPA's sealing guide says that in most homes the most significant air leaks are hidden in the attic and basement. In cold weather warm air rises through the house the way smoke rises in a chimney, escapes through gaps at the top, and pulls cold air in low down to replace it, so the draft you feel along a window or the floor is often driven from the attic. ENERGY STAR adds that the leaks in a typical home's envelope, added together, equal a window left open every day of the year.
St. Louis supplies the cold to drive it: Lambert's 1991–2020 NOAA normals show 4,433 heating degree days and 84.9 nights a year that reach 32°F or colder. Other signs on ENERGY STAR's list for attic sealing: hot and cold rooms, high bills, ice dams, dry indoor air in winter, and dust, especially in rooms right under the attic.
Sealing, every time, because the two do different jobs. ENERGY STAR defines air sealing as using materials such as caulk or foam to stop air flow, while bulky insulation like fiberglass or cellulose mainly resists heat conducted through it and, to a lesser degree, heat carried by moving air. Lay insulation over open holes and house air keeps filtering through it; the dark, dirty patches EPA's guide tells you to look for are exactly that, and in cold weather the same spots can show frost.
The material follows the size of the gap, per ENERGY STAR: caulk for cracks of 1/4 inch or less, expanding foam from 1/4 inch to about 3 inches, rigid foam board, foil or drywall over open soffits and larger holes, and metal flashing with high-temperature caulk around flues, where building codes usually require 1 inch of clearance from metal flues and 2 inches from masonry chimneys. Then the insulation goes back on top.
At the attic floor and along the foundation, the two ends of that chimney effect. ENERGY STAR's guide lists where to look, line by line:
Ameren Missouri's 2026 sheet names similar ground for its measure: attic penetrations and top plates, crawl space penetrations, openings under sinks, interior equipment closets, doors and windows, and switch and outlet covers.
How leaky the whole house is, as a number, and where the leaks are. In ENERGY STAR's description, a blower door is a strong fan fitted into an exterior doorway that pushes or pulls air to change the pressure inside and exaggerate every leak. DOE's consumer guide adds that a calibrated blower door, read on a pressure gauge called a manometer, measures how much air is leaking; one without that gauge can find leaks but not size them. Run alongside an infrared camera, leaks show up as black streaks in the image.
That number is what the utility money rests on. Ameren Missouri's incentive needs sealing that can cut leakage by 20 percent, and Ameren Illinois pays per CFM removed, so both need a measured before and after. It is a code instrument for new houses as well: under Cottleville's amended code, a new home may leak no more than 5.0 air changes an hour, or alternatively 0.28 cfm per square foot, at a test pressure of 0.2 inch of water. We run it before and after the work wherever the job calls for one.
For many houses it is a day's work rather than a renovation, after an assessment of about an hour, and ENERGY STAR estimates one to two days for a contractor sealing an attic. What adds time: insulation that has to be pulled back from the top plates and put back, a finished attic with kneewalls, dropped soffits that need rigid covers, flues that need metal dams, rim joists hidden behind finished basement walls, and a blower door test at each end. On the Illinois side the schedule also waits on Ameren Illinois, since its approval has to come through before the work starts.
It can be, with the checks EPA's ENERGY STAR program spells out. Sealing can trap indoor pollutants such as carbon monoxide, radon and volatile organic compounds, so a tighter house may need added ventilation; Ameren Illinois' 2026 table carries $225 per home, through a Program Ally, toward ENERGY STAR exhaust ventilation, its ASHRAE line. After reducing air leaks, EPA recommends testing for radon. And where a furnace, boiler or water heater burns gas or oil, ENERGY STAR advises having it tested before and after sealing to confirm it still drafts properly, since sealing can cause a naturally venting appliance to back-draft exhaust into the house. A combustion safety test, in ENERGY STAR's definition, checks for fuel leaks and carbon monoxide and confirms that waste gases leave through the chimney or vent.
No published rule in the metro asks for one. Across the 45 jurisdictions we cover, no permit list names air sealing. St. Louis County's list of work that needs no permit leaves caulking, weatherstripping and air sealing unmentioned, and Washington's code exempts residential remodel work with no structural, electrical or plumbing change. Silence is not an exemption, so we check with the building department and pull a permit wherever one is required.
On the Illinois side the state energy code reaches remodeling: Illinois law applies it to the portion of a building being altered, and Edwardsville's remodel handout sets minimum insulation levels for remodel work. Missouri codes change from city to city; St. Louis City, for one, enforces the 2018 IECC. The energy code guide has the table.
It depends on the meter, the heating fuel and the side of the river. Ameren Missouri counts only electric bill savings when it works out a PAYS copay, and it says homes heated by electricity see higher year-round savings and so a lower copay. That matters most in Jefferson and Franklin counties, where most occupied homes heat with electricity by the Census Bureau's count. Kirkwood is one exception on the Missouri side, with a city-owned electric utility that publishes no air sealing rebate, and homes in parts of St. Charles County served by the Cuivre River Electric cooperative find none on its rebate list either. Spire, the gas utility, co-delivers Pay As You Save with Ameren Missouri and names air sealing among its measures.
In Illinois the discount is paid per CFM, so the blower door number decides it. And the heat counts too: Lambert also logs 47.1 days a year that reach 90°F, plus 1,713 cooling degree days, so a leaky house pays for it in summer as well.
A test that shows how airtight a house is and helps locate its leaks. A fan set into an exterior doorway changes the pressure inside so every gap leaks harder, and a calibrated gauge turns the result into a leakage figure. Run before and after sealing, it shows how much the work achieved.
ENERGY STAR rates attic air sealing a challenging do-it-yourself job. It recommends a professional when access is difficult, the insulation is wet, rafters show mold or rot, a kitchen, bath or dryer vent empties into the attic, ventilation is poor, or there is knob-and-tube wiring. If you find vermiculite, EPA says not to disturb it.
Inside Pay As You Save, yes: the 2026 sheet lists $0.06 per square foot, as long as the work can cut leakage by 20 percent. You need to be in tier 4 of the program with 12 months in the home, and the remaining cost is repaid through a fixed charge on the Ameren Missouri electric bill.
Yes. Its 2026 discount table pays $0.70 per CFM of leakage removed, applied by a registered Program Ally. The order is Ameren's own: an eligibility check, then the Program Ally's home energy assessment, then a project application showing the estimated discount, all before the work.
A tighter house holds onto more of what is in its air, which is why ENERGY STAR says added ventilation may be needed and EPA suggests a radon test once the leaks are reduced. Gas or oil appliances that vent naturally should be checked for proper drafting before and after the work.
Usually, yes. EPA's guide says that even with enough insulation in the attic, sealing the leaks beneath it improves how that insulation performs and makes the house more comfortable. Dark, dirty patches in the existing insulation are the clue that air is still moving through it.
Air sealing across greater St. Louis, from the city and St. Louis County out to St. Charles, Jefferson and Franklin Counties and across the river into the Metro East. Each city has its own page with the permit rule and code edition that apply there:
Sources: ENERGY STAR attic air sealing project · EPA / ENERGY STAR do-it-yourself guide to sealing and insulating (2016) · ENERGY STAR savings methodology (climate zone table) · ENERGY STAR: why seal and insulate · ENERGY STAR home performance glossary · DOE consumer guide to home energy assessments · Ameren Missouri Pay As You Save 2026 incentive sheet · Ameren Missouri Pay As You Save · Ameren Illinois insulation and air sealing discounts, 2026 · Spire Pay As You Save · IRS: Energy Efficient Home Improvement Credit · NOAA 1991-2020 U.S. Climate Normals · U.S. Census Bureau ACS 2020-2024, table B25040 · St. Louis County: work that does not require a permit · City of Washington, MO building code · Cottleville, MO residential code amendments · Edwardsville remodel requirements · City of St. Louis adopted building codes · Illinois Energy Conservation Code (Capital Development Board) · Kirkwood Electric energy efficiency · Cuivre River Electric Cooperative rebates. Codes, programs and prices change; confirm the current rule with your city before you rely on it.
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