Attic insulation in St. Louis

What does attic insulation cost in St. Louis?

We publish no price list, because two attics with the same floor area can be very different jobs. You get a measured R-value and one line-itemed proposal before anything is booked. The price moves with the square footage, the R-value now and the target; how many top plates, holes, chases and dropped soffits need sealing; access, headroom and the number of soffit bays to baffle; old material that is wet or rodent-fouled and has to come out; and fixes that must come first, such as live knob-and-tube wiring or a bath fan venting into the attic.

• Ameren Missouri: its Pay As You Save sheet for January 1 to December 31, 2026 lists $0.20 per square foot of ceiling or attic insulation, for an attic that starts at R-20 or less and ends at R-38 or more, in tier 4 of the program, after at least 12 months in the home. A program partner installs it after Ameren's free assessment, and the balance comes back as a fixed monthly line on the electric bill, held to no more than 80 percent of the estimated savings. CommunitySavers insulates attics at no cost for households that meet its income tests, through December 31, 2026 while funds last.
• Ameren Illinois: $1.10 per square foot of attic insulation on its 2026 discount table, deducted from the contractor's price; only its registered Program Allies can offer it.

There is no federal credit to add: 25C stopped with work placed in service by the end of 2025.

How much insulation does a St. Louis attic need?

R-60 for a bare attic floor and R-49 for one already holding 3 to 4 inches, by ENERGY STAR's zone 4A table. Depth depends on the material. To estimate what is already up there, ENERGY STAR multiplies inches by about 2.5 for loose fiberglass, 3.7 for cellulose and 3.2 for fiberglass batts. On those factors (our arithmetic, not a bag label), R-49 is roughly 20 inches of loose fiberglass or 13 of cellulose, and R-60 about 24 or 16.

Check yours from the hatch. If the insulation is level with or below the tops of the joists, ENERGY STAR says you probably need more; if the joists are buried out of sight, more may not pay. Look at the eaves too, since some attics are deep in the middle and thin at the edges. Three to four inches of batts comes to about R-10 to R-13, under the R-20 line in Ameren Missouri's attic condition.

Blown-in fiberglass or cellulose: which suits your attic?

Either works once it reaches the target R-value; the differences are depth, program rules and what is already there.

• Depth: at ENERGY STAR's factors, cellulose gives about R-3.7 an inch and loose fiberglass about R-2.5, so cellulose reaches a target in fewer inches. That counts most at the eaves of a shallow roof, where there is little height above the wall plate.
• Looks: ENERGY STAR describes loose fiberglass as light yellow, pink or white fibers, and cellulose as small gray flakes made from newsprint.
• Program rules: Ameren Missouri's 2026 sheet describes its attic measure as blown-in cellulose to R-38 or more, marked with depth gauges it calls R-sticks. Ameren Illinois' table pays per square foot and names no material.
• Mixing: new insulation need not match the old, says ENERGY STAR; loose fill can cover batts, and batts laid over loose fill must be unfaced.

We blow both, and the proposal names the material, the R-value and the depth it takes.

What should an attic insulation quote include?

Every step, in order. Ours is one line-itemed proposal; whoever you hire, look for these lines:

• Existing insulation measured and photographed: type, depth, condition, R-value.
• Air sealing first: top plates, wire and plumbing holes, chases, dropped soffits, and the flue gap, which ENERGY STAR says takes metal flashing and high-temperature caulk, never spray foam.
• Baffles at every soffit bay. ENERGY STAR calls them rafter vents; they keep the soffit vents open so insulation can reach the outer edge of the attic floor.
• Dams around recessed lights not rated IC, since ENERGY STAR keeps insulation 3 inches from them.
• The hatch or pull-down stairs weatherstripped and insulated, the way ENERGY STAR's guide would treat an exterior door.
• Material, target R-value and finished depth, with the depth on a ruler at the hatch.
• A blower door test before and after where the job calls for one, photographs of the finished work, and the permit if the city requires one.

How long does an attic insulation job take?

The assessment takes about an hour, and for many houses the installation is a day's work rather than a renovation; ENERGY STAR puts a contractor-installed attic project at one to two days. Floors are protected, the ceiling is sealed while it can still be seen, then come the baffles, the hatch and the insulation, and the finished depth is photographed. Jobs run longer when old insulation has to come out first, when a finished attic has kneewalls and open floor cavities, when the attic floor is crowded with penetrations or flues that need metal dams, or when a roof leak, a misrouted vent or live knob-and-tube wiring has to be fixed first.

What has to be checked before insulation is blown in?

Two findings stop an attic job outright, and ENERGY STAR names others to fix first.

• Vermiculite: pebble-like, poured-in granules, usually gray-brown or silver-gold, per EPA. Most vermiculite sold in the U.S. from 1919 to 1990, over 70 percent, came from one mine near Libby, Montana, and it was contaminated with asbestos. EPA says to assume yours contains asbestos and leave it alone; anyone remodeling around it should bring in a professional asbestos contractor. We neither blow over it nor remove it; it is referred out.
• Knob-and-tube wiring: ENERGY STAR dates it to before 1930 and calls it a fire hazard in contact with insulation, and NEC section 394.12 bars it from spaces where loose, rolled or foamed-in-place insulation would envelop the wires. Live circuits get rewired or shut off first.
• Other warning signs: wet insulation from a roof leak, moldy or rotted framing, a kitchen, bath or dryer vent exhausting into the attic, or little to no ventilation.

Do you need a permit to insulate an attic in St. Louis?

Where a rule is published, it says no permit; most of the metro publishes nothing either way. Six of the 45 jurisdictions we cover fall under a published rule that reaches an attic top-up. St. Louis County's list of work exempt from a building permit includes increasing attic insulation, and the county desk applies it in unincorporated St. Louis County, Affton, Oakville and Mehlville among them; Wildwood uses the same list. Washington exempts residential remodeling with no structural, electrical or plumbing change. The other 39 publish no permit rule for insulation either way, so we call the building department first and pull a permit wherever one is needed.

New-house codes are a separate matter. Thirty-two of the 45 carry an attic figure: R-49 in 27, R-60 in Kirkwood, Florissant and Clayton on the 2021 IECC, and R-38 in St. Peters and Cottleville, which amended the table down. Retrofits vary: Illinois law applies its code to the part of a house being altered; Jefferson County deleted the existing-buildings chapter, so its code does not reach an attic in Imperial; and Pacific and Union cut the energy chapter from their residential codes. The code and rebate guide has the full table.

Why is the upstairs hot in July and cold in January?

A thin or leaky attic floor is the first suspect. ENERGY STAR's symptoms for an attic project read like the complaint: hot or cold ceilings and rooms, uneven temperatures, high bills, ice dams. St. Louis loads an attic both ways; Lambert's 1991–2020 NOAA normals average 47.1 days a year at 90°F or above and 84.9 nights at 32°F or below.

Two cautions before buying a fix. A powered attic fan over an attic with blocked soffit vents and no seal from the house pulls cooled air out of the rooms below, ENERGY STAR's guide warns. And the same guide counts ice dams, snow melted by a warm attic that refreezes at the gutter, as a sign of serious air leaks, which is why sealing comes before depth.

What makes a St. Louis attic different?

The housing, the climate and a state line. The eight counties we cover hold about 1.18 million homes, 59 percent of them built before 1980, in the Census Bureau's 2020–2024 American Community Survey. Median build years run from 1939 or earlier in the city of St. Louis and 1969 in St. Louis County to 1994 in St. Charles County, with Madison County at 1971 and St. Clair at 1975. ENERGY STAR dates knob-and-tube to before 1930; the Census does not split out the 1930s, but the city alone counts 100,811 homes built in 1939 or earlier.

Missouri has no statewide residential code, so local editions on this side range from the 2015 IECC to the 2024; Illinois enforces one statewide code, now the 2024 IECC with Illinois amendments, in effect since November 30, 2025. And not every Missouri address is an Ameren Missouri customer: Kirkwood has its own electric utility, which publishes no attic rebate, and the Cuivre River cooperative serves parts of St. Charles County without a standalone insulation rebate.

Common questions about attic insulation in St. Louis

Where we work

Attic insulation 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: