St. Louis City is independent from St. Louis County (since 1876). Building Division, 1200 Market St, Room 426. Missouri has no statewide building code. 70% of permits issued same-day; Hot Spot Desk Mon & Wed 9am–3pm. Online portal launched March 2026.
St. Louis window replacement permit rules
The 2018 IRC egress triggers apply: bedroom windows need permits for egress compliance (5.7 sq ft clear area, 44-inch sill max, 20-inch width min, 24-inch height min). Same-opening non-bedroom replacements are typically permit-exempt. IECC Zone 4A requires U-factor ≤ 0.32 and SHGC ≤ 0.40 for all replacement windows — identical U-factor requirement to Madison, the same heating-climate logic. Verify the NFRC label on every window before purchase.
St. Louis's brick housing stock creates a distinctive window installation requirement: windows set in masonry openings (not stud-frame openings) require careful flashing into the brick — a different technical requirement than standard stud-frame window replacement. In historic districts, the Cultural Resources Office (314-657-3865) reviews visible window changes. Original wood double-hung windows in St. Louis's Victorian architecture are character-defining features; replacement with vinyl sliders of different profile may not receive Cultural Resources approval.
Three St. Louis window replacement scenarios
| Window Situation | Permit? | Zone 4A Spec | St. Louis Note |
|---|---|---|---|
| Bedroom, same opening | Yes — egress | U ≤ 0.32; SHGC ≤ 0.40 | Brick masonry flashing critical |
| Living/dining, same opening | No permit | U ≤ 0.32; SHGC ≤ 0.40 | No inspection but specs still apply |
| Enlargement in brick wall | Yes — structural | Lintel engineering required | Steel lintel for new masonry span |
| Historic district window | Yes + Cultural Resources | Period-compatible profile | Contact 314-657-3865 before ordering |
Zone 4A window specifications — U-factor priority
St. Louis's IECC Zone 4A requires U-factor ≤ 0.32 — identical to Madison's Zone 6 in U-factor specification, though for different thermal reasons. In St. Louis's mixed climate, winter heat loss prevention (U-factor) is the primary concern, while some solar gain (SHGC ≤ 0.40, more permissive than Chandler's desert ≤ 0.25) can be beneficial in winter for passive solar heating. For older St. Louis homes with original single-pane wood windows (U-factor approximately 0.90–1.10), upgrading to modern double-pane low-e (U-0.27) delivers a 70–75% reduction in window heat loss — the highest-impact single envelope improvement available in most older St. Louis homes.
What the inspector checks
Bedroom egress: sill ≤ 44 inches, clear width ≥ 20 inches, clear height ≥ 24 inches, total ≥ 5.7 sq ft. NFRC label verification. For rough openings in brick: lintel adequacy. Call 314-622-3315.
What window replacement costs in St. Louis
Standard vinyl double-pane low-e: $270–$520/window installed. Fiberglass: $420–$850. Period-compatible historic: $550–$1,400. Whole-house (12): $6,500–$14,500. Permit fees: ~$150–$250 for bedroom windows.
Do bedroom windows require a permit in St. Louis?
Yes — 2018 IRC sleeping room window replacements require permits: 44-inch max sill, 20-inch min clear width, 24-inch min clear height, 5.7 sq ft min total clear opening. Hot Spot Desk (Mon & Wed 9am–3pm, 314-622-3315) can process same-day.
What window specs are required in St. Louis?
Zone 4A: U-factor ≤ 0.32 and SHGC ≤ 0.40. U-factor identical to Madison — heat loss prevention is the primary concern in the heating-significant climate. SHGC ≤ 0.40 more permissive than Chandler's desert ≤ 0.25. Verify NFRC-labeled values before purchasing any window.
How are windows replaced in a brick St. Louis home?
Replacement in masonry openings requires removing the existing window, cleaning the masonry opening, installing flashing (critical for waterproofing at brick-window interface), setting new window unit, shimming level and plumb, securing with masonry fasteners, and sealing with masonry-compatible sealant. Brick openings are typically fixed size — windows must fit existing masonry dimensions or the opening must be enlarged with a steel lintel.
What is a lintel and why does it matter for window enlargement?
A lintel is the horizontal structural element spanning a masonry opening carrying the weight of brick above. Enlarging a window opening in a brick St. Louis home requires a properly sized steel lintel for the new span. The lintel must be engineered for the load, properly supported during installation, with brick shored above. Plan reviewer verifies lintel design at permit submission.
Do historic district homes have special window requirements?
Yes — Cultural Resources Office (314-657-3865) reviews visible window changes in 14 historic districts and 112 City Landmarks. Original wood double-hung windows are character-defining features. Period-compatible wood or fiberglass replacements, or interior storm inserts, are typical approved alternatives. Contact Cultural Resources before ordering.
Are Ameren Missouri rebates available for window replacements?
Ameren Missouri has historically offered energy efficiency incentives for qualifying window replacements. Verify current program availability at ameren.com before purchasing. Federal IRA home improvement energy credits may also apply. Consult a tax professional.
General guidance based on publicly available municipal sources as of April 2026. City of St. Louis uses 2018 IRC. Historic districts: Cultural Resources at 314-657-3865. Verify at 314-622-3315. For a personalized report, use our permit research tool.
Phone: 314-622-3315 (Hot Spot Desk: Mon–Wed 9am–3pm)
Hours: M–Th 8am–4:30pm, F 8am–4pm
Online: stlouis-mo.gov/building/permits
Codes: 2018 IRC · 2017 NEC · 2021 UPC · 2018 IECC
Cultural Resources: 314-657-3865 · Spire: spire.com · Ameren MO: ameren.com
Missouri One Call: 800-344-7483