In the City of St. Louis you do not need a building permit to replace windows in the same opening, unless the house is in a historic district, where the Cultural Resources Office must approve first. In unincorporated St. Charles County you do need a permit once the job is four or more windows, even at the same size. Enlarging or adding an opening is a structural change and needs a permit under any adopted residential code. And in St. Louis County — one county, roughly ninety municipalities — the answer depends on which city you are in.
The verified rules
| Jurisdiction | Same-size replacement | Enlarge / add opening | Building code | Fees | Status |
|---|---|---|---|---|---|
| City of St. Louis (Building Division) | No permit. The City's residential permit criteria list, under work that "usually does not require a permit," "replacement or repair of existing windows and frames, whenever no modification is made to the opening," and separately "installation of storm windows and doors, glazing and glass replacement." | Permit required: "any structural change or major alteration" and any work "cutting … structural beams." | 2018 IRC, IBC, IEBC and IECC, adopted August 1, 2018 (Ordinances 70794–70802 cover the 2018 code set); 2021 UPC. | $25 application fee; permit fee $19 up to $1,000 of work, $23 to $2,000, $30 to $3,000, then $10 per $1,000 above that. | ✔ |
| City of St. Louis — City Historic District or City Landmark | CRO approval required before any permit. The same criteria page: a permit "is usually required by the Cultural Resources Office even though it is not required by the Building Code." The CRO: "No permit may be issued without the Cultural Resources Office or the Preservation Board's approval." | Same, and most districts prohibit altering street-façade openings. | — | CRO review itself has no separate published fee on the page read; permit fees as above. | ✔ |
| St. Charles County (unincorporated) | No permit for three or fewer windows in the same opening: County Code §500.150, R105.2, exempts "Replacement of three (3) or less doors and/or windows where the opening size is not increased or decreased." Four or more: permit required. | Permit required. | 2021 St. Charles County Residential Code (2021 IRC with amendments). | Set by the governing authority; schedule not in the code document. Confirm. | ✔ rule / confirm fee |
St. Louis County and its municipalities
St. Louis County's Department of Public Works issues permits for unincorporated areas and for the municipalities that contract with it; the larger cities run their own desks. We could not verify the County's same-size replacement rule from its published code on this update, and each municipality's rule has to be read from its own code. The table is what to confirm, with what we know:
| Jurisdiction | What we know | Status |
|---|---|---|
| St. Louis County (unincorporated and contracting munis) | Permit rule for same-size replacement not verified. Ballwin requires an "active St. Louis County License in their respective field" to pull a permit, so a County trade-licence class exists; which class covers window installation is unverified. | confirm |
| Ballwin | Every contractor working in the city needs a Ballwin contractor's licence before pulling permits, with workers' comp (or exemption affidavit) and an active St. Louis County licence; applications through the MyGov permit portal since November 1, 2025. Window permit rule, fee and code edition not verified. | ✔ licence / confirm rule |
| Chesterfield, Kirkwood, Webster Groves, University City, Florissant, Clayton, Maplewood, Richmond Heights, Creve Coeur, Des Peres, Manchester, Hazelwood, Ferguson, Bridgeton, Maryland Heights | Each runs its own building department; rules for same-size replacement, fees and code edition not verified on this update. Kirkwood, Webster Groves and University City also have local landmark or historic-preservation provisions that may apply to street-facing windows on designated properties. | confirm |
| St. Charles, St. Peters, O'Fallon, Wentzville, Lake St. Louis, Cottleville (St. Charles County municipalities) | Each issues its own permits; the County's three-window exemption applies only in unincorporated areas. Not verified. | confirm |
| Arnold and Jefferson County | Not verified. | confirm |
| Edwardsville, Belleville, Collinsville, Granite City, Alton (Illinois) | Illinois municipalities register or license contractors locally and run their own permit desks; same-size replacement rules not verified. Illinois has no statewide general-contractor licence (roofing is state-licensed). | confirm |
We update this table as we verify rows. If you want the rule for your city before you order, say so on the quote form and we confirm it at the measure.
Why the historic district line matters more than the permit line
In the City, the building code's exemption for same-size window replacement is real, and it lulls people. But eighteen City neighborhoods sit inside ordinance-designated historic districts, and there the question is not "do I need a building permit" but "will CRO approve the window." The approved list contains no vinyl product, and every district standard we have read requires wood, clad wood, composite or color-finished aluminum on street-facing façades, replicating the original. The whole rulebook is in the historic district window rules guide.
Egress: the rule that applies without a permit
Whether or not a permit is pulled, a bedroom window has to work as an emergency escape and rescue opening. The residential code's minimums are a net clear opening of 5.7 square feet (5.0 at grade), at least 24 inches high and 20 inches wide, with the sill no more than 44 inches above the floor. The code's replacement-window provision exempts a replacement from the sill-height and opening-area minimums where the new unit is the manufacturer's largest standard size that fits the existing frame and there is no change of occupancy — which is why a same-size replacement in an old bedroom is lawful even if the original opening was undersized. Converting a basement into a bedroom is different: that is a new egress opening, a cut, a well, and a permit everywhere.
Contractor licensing in the region
- City of St. Louis: contractors need a Construction Industry Contractor Graduated Business License from the License Collector, and general contractors must furnish a list of subcontractors on a job.
- Missouri: no statewide general-contractor licence; licensing is municipal and county. (This Old House's St. Louis page notes the same.)
- Illinois: no statewide general-contractor licence; roofing contractors are state-licensed; municipalities register contractors.
- Lead: separately from any of the above, a firm replacing windows in a pre-1978 house must be an EPA Lead-Safe Certified Firm, in both states. See lead-safe window replacement.
Frequently asked questions
If no permit is needed, does anyone inspect the work? No. That is why the written quote matters — it is the only document that says what was supposed to be done.
Does an HOA count? An HOA's architectural review is a private covenant, not a permit, but in St. Charles County's subdivision belt it is often the stricter of the two for exterior color and grid style. Check it before ordering.
What happens if a contractor skips a required permit? The owner can be made to obtain one after the fact, and a sale can be held up by unpermitted work. In St. Charles County unincorporated, at four windows, it is required.
Who pulls the permit, me or you? We do, where one is required, as part of the job.
Next step
Window replacement includes permit and CRO handling where they apply. Related: the complete St. Louis guide · the St. Charles County page · the City page.