Wall insulation in St. Louis

What are your walls made of?

• Balloon framing. A stud bay can run open from the basement to the attic. DOE's Building America guide says those bays need blocking at both ends before dense-packing, or the fill drops through.
• Platform framing. Plates close the top and bottom of each story's bays. The easiest wall to fill.
• Solid brick. Several layers of brick carry the house, plastered directly or over wood furring strips. No stud cavity. DOE's masonry guideline puts such a wall, uninsulated, at roughly R-3.2 to R-6.8, about R-5 on average.
• Brick veneer. One layer of brick in front of a stud wall, whose bays can usually be filled from inside.

We sort out which you have by viewing a cavity at an outlet with the power off or through a small test hole, and with an infrared camera.

Dense-pack cellulose or injection foam?

For an empty frame cavity, dense-pack is the usual answer and injection foam the alternative. On federal figures where they exist:

• R per inch: dense-pack cellulose about R-3.2 to R-3.5; injection foam, whatever the product's data sheet states.
• Fill: cellulose is blown to 3.5 to 4.5 pounds per cubic foot, tight enough not to settle; foam-in-place insulation is blown into the wall and fills even small voids.
• Air: dense-pack slows air through the bay; foam reduces air leakage as it fills.
• Water: cellulose tolerates a little moisture but breaks down if soaked; foam depends on the product.
• Material: cellulose is recycled newspaper and boxes treated against fire; injection foams are branded products with their own limits.

Dense-pack fiberglass is a third choice, about R-4.2 per inch at 1.8 to 2.6 pounds per cubic foot and not ruined by a soaking. Cellulose is what DOE-funded low-income weatherization programs favor for dense-packing. If injection foam is proposed, the quote should name the product and its published R-value.

From inside or outside: where do the holes go?

• Inside. One hole per stud bay, one or two inches across, about six inches below the ceiling, plus extra holes under blocking and in the short bays over doors, around windows and behind cabinets. The siding and the weather barrier behind it are not touched.
• Outside. Holes go through the siding or sheathing. DOE's guide calls re-siding the ideal moment, and DOE and ENERGY STAR both advise that whenever siding comes off an uninsulated frame wall, the empty cavities get drilled and blown full and insulating sheathing goes on before the new siding. Any weather barrier that is opened must be repaired.

Slumped old batts can block the fill; DOE's guide pulls them through a strip cut near the floor or confirms with infrared that the new fill went around them. Thermal imaging checks the bays before the holes close, while a void is still easy to fix.

What does wall insulation cost in St. Louis?

A wall job is priced from the house itself, not from a sheet. The drivers:

• Square feet of exterior wall and the number of stories.
• Wall type: platform frame is simplest, balloon frame needs blocking, solid brick is a renovation.
• Access side: plaster and lath inside, or siding outside.
• The count of short bays around windows, doors, stairs and cabinets.
• Work that must come first, such as an electrician retiring knob-and-tube wiring.

The free assessment covers the framing, the cavities, an infrared scan and photographs, in a report you keep either way, and the proposal lists each wall, material and drill side on its own line.

In Illinois, the wall line on Ameren Illinois' 2026 table is $1.10 a square foot for filling empty exterior wall cavities, applied by a registered Program Ally as a cut in the price. In Missouri, Ameren's 2026 Pay As You Save sheet carries no wall measure at all; its weatherization lines are ceiling and attic insulation, air sealing and duct sealing, the same trio Spire's on-bill program names. Households with qualifying incomes can apply for weatherization through their county's designated agency on either side of the river. The federal 25C credit is no help for 2026 work; it closed to anything put in service after December 31, 2025.

How long does it take, and what does the visit look like?

Plan on about an hour for the assessment. For walls it means an outlet cover off, an infrared pass around each floor and a look at the attic and basement ends of the bays. The install runs longer with more stories, plaster and lath instead of drywall, balloon framing that needs blocking, many short bays around windows, or an old finish to match. Furniture comes away from the outside walls, floors are covered, and holes are plugged only after the infrared check shows full bays.

What is included in a wall insulation job?

• Framing identified and a cavity viewed, so the plan fits your wall.
• A check for live knob-and-tube and for vermiculite poured into the walls. The National Electrical Code forbids concealed knob-and-tube inside hollow walls once loose or foamed-in-place insulation surrounds the wires, so an electrician rewires or retires those circuits first. Vermiculite we refer out and leave in place, as EPA advises.
• Blocking at the top and bottom of balloon-framed bays.
• Each bay packed to the maker's dense-pack density.
• An infrared scan for voids before any hole closes.
• Holes plugged and patched, floors covered throughout.
• Your photo report, and any permit your town requires, handled by us.

Do you need a permit to insulate existing walls?

Rarely in writing: 42 of the 45 jurisdictions this site covers publish nothing we could find about insulation permits. The exceptions:

• Unincorporated St. Louis County needs no permit to insulate exterior walls beneath new or replacement siding, but does for insulation, furring and drywall added on the inside of an exterior wall. Insulating a solid brick wall from inside, with new framing and drywall, falls on the permit side.
• Wildwood follows the county's list.
• Washington exempts residential remodeling that changes no structure, wiring or plumbing, or costs under $1,000.

New walls in additions do face an energy-code R-value, which varies by town. We check with the building department before scheduling, and permits are ours to pull.

A second rule applies to older houses whatever the city says. In housing built before 1978, paid work that disturbs painted surfaces, such as drilling plaster inside or lifting painted siding outside, falls under EPA's Renovation, Repair and Painting rule unless testing shows the paint is lead-free. EPA requires the firm doing covered work to hold its own EPA firm certification, sole proprietors included, so ask to see it; inside, work that disturbs six square feet of paint or less per room is exempt as minor repair. Neither Missouri nor Illinois runs its own version; EPA administers the rule directly on both sides of the river, and before the work starts the homeowner receives EPA's Renovate Right pamphlet.

Why do the outside walls feel cold?

In an old frame house, look for empty walls with bays open at both ends. Air can rise from the basement up an open balloon-framed bay and out into the attic; DOE's guide has each end blocked before the bay is filled, which closes that path as well. Plaster on furring strips leaves a gap behind it that DOE's masonry guideline names as a leakage path. On a cold day an infrared scan shows empty bays and moving air as cold patches. Filling those bays and sealing the attic floor above them changes how the rooms feel; the attic insulation and air sealing pages cover the top of the wall.

St. Louis walls by the numbers

Old housing is concentrated in the city and the inner ring. Homes built in 1939 or earlier, from the Census Bureau's American Community Survey five-year estimates for 2020-2024:

• St. Louis city: 57.9%, an estimated 100,811 of 174,111.
• Missouri counties: St. Louis County 9.7%, Franklin 9.9%, Jefferson 3.5%, St. Charles 2.2%.
• Illinois counties: Madison 14.6%, St. Clair 13.5%, Monroe 9.8%.

By those estimates the city has more pre-1940 homes than the other seven counties put together, 100,811 against 89,262. In the inner ring the share reaches 42.6% in Richmond Heights, 38.1% in University City and 35.1% in Webster Groves; across the river Alton sits at 27.6%.

Freezing matters to old brick. At Lambert, NOAA's 1991-2020 normals average 84.9 freezing nights a year against 19.3 days whose high stays at or below 32°F. DOE's masonry guideline treats climate zone 4 and colder as the higher-risk group for insulating brick from inside, and all of this metro is zone 4A. For new walls the code spread is wide: R-13 in St. Peters and Cottleville; R-20 in the cavity, or R-13 with R-5 of continuous insulation, under the 2015 and 2018 editions; R-30 or a mix with continuous insulation in Kirkwood, Clayton and Florissant; and, statewide in Illinois, a cavity of R-20 or R-13 paired with R-5 or R-10 of continuous insulation, respectively.

Common questions about wall insulation in St. Louis

Where we work

Wall 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: