Window Replacement in St. Louis

Full-frame or insert: let the opening decide

An insert is a complete new window, frame included, set inside the old frame. The old jambs, sill and interior casing stay put, so plaster and trim are left alone. A full-frame job strips the opening back to the rough framing or masonry and rebuilds it with a new unit, new flashing and new trim.

It comes down to condition, and you can check most of it yourself:

• Push a screwdriver into the sill and the bottoms of the side jambs. Wood that gives is rot, and an insert would be fastened into it.
• Look for stains on the wall below the window and at the ends of the inside sill. Water that got past the old window will get past an insert sitting in the same frame.
• Measure corner to corner both ways. When the two diagonals disagree, the frame has racked, and a square new unit will not seal in it.
• Changing the size of an opening always means full-frame.

On a sided house, full-frame work opens the siding around the window, which is the one chance to fit a sill pan and lap the head flashing correctly. In a brick wall, an insert can keep the outside brick mold and the inside plaster returns intact. One house can need some of each.

Vinyl, fiberglass, wood or clad wood

The National Fenestration Rating Council notes that sash and frame make up 10 to 30 percent of a window's area, which is why the label's U-factor covers the whole unit, not just the glass. Past that, frame material is mostly a choice about upkeep, looks and budget:

• Vinyl windows never need paint and cost less than wood. They are not white-only anymore; the regional cost figure below is for vinyl with a custom exterior color.
• Fiberglass windows cost more than vinyl; the buying guide covers how each frame ages.
• Wood suits an older house and asks the most of you. The National Park Service names moisture as the main cause of decay in wood windows, so paint and glazing upkeep come with them.
• Clad wood wears a factory-finished skin outside and shows wood inside. The 2025 Cost vs Value wood window is this type: stained hardwood in, custom-color aluminum out.

Then check whether the choice is yours. Inside a City of St. Louis historic district, the ordinance can set the material: Shaw allows wood or color-finished aluminum frames, and Lafayette Square wants wood on public-facing windows (historic district rules). Kirkwood's design guidelines ask for one window type, style, material and color across every facade. In Clayton, a visible window change goes through architectural review, $135 before the full board or $85 on the administrative track, on top of the permit.

Double-hung, casement or slider

• Double-hung windows keep the traditional look, and tilt-in sashes let you wash the outside glass from indoors. They never open more than about half the frame.
• Casement windows swing the whole sash out, so the same frame size gives a bigger opening. The hinge hardware eats some of the clear width, so the exact model matters when the window has to be an escape route.
• Sliders suit wide, short openings such as basement and over-counter windows. Like a double-hung, they open half.

Switching styles is allowed, but it can change your permit. Unincorporated St. Louis County, and the cities that use its rules, exempt a same-opening swap only if the new window keeps the old operating style or opens at least as much (county rules). Unincorporated Jefferson County drops the exemption the moment the operation changes at all (Imperial). Upstairs, a low sill brings in the code's fall rule, R312.2: where an operable opening starts less than 24 inches above the floor and more than 72 inches above the ground outside, it must stop a 4-inch sphere or carry a fall prevention or opening control device that meets ASTM F2090.

What the new glass must meet in your city

Once a new sash and glass go in, the energy code (IECC R503.1.1.1) treats the unit as new, and it has to meet the U-factor and solar heat gain limits your city adopted. Swapping only the glass in an old sash does not set that off. Missouri leaves the number to each city, so it changes at city lines:

• Brentwood, on the 2024 code: U-0.28.
• Kirkwood, on the 2021 code: U-0.30.
• The City of St. Louis, on the 2018 code: U-0.32.
• Unincorporated St. Louis County writes U-0.34 into its window permit exemption.
• Wentzville set its own U-0.40, and Ballwin deleted its energy chapter.

On the Illinois side, one statewide code applies in every town. The easy way through all of it: every county we cover sits in ENERGY STAR's North-Central zone, where a qualifying window must rate at or below U-0.25, with solar heat gain at or under 0.40, and that beats every code in force here. The city-by-city list is on the window energy code page.

Safety glass where the code calls for it

The residential code names the places where glass must be safety glazing (R308.4); the full list is in the buying guide. On replacement work, four of them come up again and again:

• Bathroom windows with glass under 60 inches up from the floor you stand on and within 60 inches sideways of the tub or shower.
• Stair and landing windows whose glass starts lower than 36 inches above the steps.
• Windows within 24 inches of a door, in line with it when it is shut, with glass that reaches below 60 inches.
• Big, low picture windows: a single pane over 9 square feet that starts under 18 inches off the floor and ends above 36, with somewhere to walk within 36 inches.

Each pane in those spots needs a permanent mark, etched, sandblasted, ceramic-fired, laser etched or embossed, that names who applied it, the glass type and the safety standard it meets (R308.1). That mark is what an inspector, and later a buyer's inspector, looks for. Enlarging a window can move it into one of these groups; Town and Country requires a permit when a bigger window ends up needing tempered glass. We check every opening against this list before anything is ordered.

On a pre-1978 house, the lead rule comes with every window

EPA's lead rule has a small-job exemption, and window replacement is excluded from it at any size (40 CFR 745.83). So on a house built before 1978, every window that comes out comes out under the Renovation, Repair and Painting rule. That reaches a lot of this metro: more than half the homes in the City of St. Louis were built before 1940. At a window, EPA's work practice standard (40 CFR 745.85) looks like this:

• Inside: furniture and window coverings moved out or covered, ducts in the area sealed, and plastic taped to the floor at least six feet out from the work.
• Outside: the ground covered at least ten feet out, and doors and windows within 20 feet kept shut.
• Banned methods: open-flame burning, power sanding or planing without a shroud and HEPA vacuum, and heat guns at 1,100 degrees Fahrenheit or hotter.
• Before you get the room back: each windowsill in the work area wiped with a damp cloth and checked against EPA's cleaning verification card.

You are also owed EPA's Renovate Right pamphlet before work begins. A bid for a pre-1978 house that never mentions any of this has left out real labor. What the firm itself must hold is on our lead paint rule page.

What window replacement costs here

The most useful public yardstick is Zonda's 2025 Cost vs Value Report. It costs out one fixed project for the West North Central division, which takes in Missouri, and has no St. Louis line of its own.

Read the project before holding a quote up to it. Both jobs replace ten 3-by-5-foot double-hungs with insulated low-E glass and simulated divided lights; the vinyl one has a custom exterior color, and the wood one is stained hardwood inside with custom-color aluminum cladding outside. Exterior trim is matched to the old, and interior trim is not touched. That is about $2,278 a window in vinyl and $2,615 in wood, for that scope only.

What moves a real quote off those lines: full-frame work that opens plaster or siding, sizes past 3 by 5, tempered glass where the code requires it, an egress change, lead-safe containment, permit fees, and rot in a sill, which gets priced against what is actually found, agreed before work starts.

How a window job runs

At the free estimate we measure every opening and check three things before quoting: the escape rule on bedroom and basement windows, safety glazing wherever the code calls for it, and the year the house was built, which decides whether the lead rule applies. Then we look up your city's permit rule and energy code. The written scope lists each opening as full-frame or insert, names the glass, and says how rot will be priced if the old sill hides some.

On install day, the house is set up lead-safe first if it predates 1978. Each old unit comes out, the opening is checked and repaired where needed, and the new window is set level and square, sealed and flashed, with the trim put back. At the final walk every window is opened, closed and locked, and on a pre-1978 house you get the lead-safe compliance summary within 30 days of finishing.

Common questions about window replacement in St. Louis

Where we work

Window replacement 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: