Window and siding replacement in Unincorporated St. Louis County

Siding replacement Conditional

St. Louis County lists re-siding among the “ordinary repairs or minor work for which a building permit will not be required.” The published item reads: “Siding: new or replaced exterior siding (vinyl, metal, wood, hardboard, etc.) including replacing with a different type of siding.” Adding exterior wall insulation under the new siding is exempt too — but insulating the inside face of the same wall is not. The exemption does not reach damage repair: a permit is required to repair a building damaged by termites, fire, wind, flood or earthquake, no matter how small the damage.

Window replacement, same opening Conditional   Enlarging or cutting an opening Permit required

Replacing windows inside the existing rough openings is exempt from permit only if the new windows clear three published conditions: they are “the manufacturer’s largest standard size window that will fit within the existing opening” and match the old operating style or give an equal or greater opening area; they have “a maximum U-Factor of 0.34”; and they meet safety glazing where it applies. Glass-only replacement in an existing sash, and storm windows and storm doors, are exempt outright. A permit is required to enlarge or modify a rough opening — and also, unusually, to replace a window with a style that gives a smaller opening area than the one it replaces.

A replacement window here has to be U-0.34 or lower

St. Louis County adopted the 2015 I-codes by Ordinance 27,654, passed 18 December 2019 and effective 1 July 2020 (moved from 1 April 2020 because of Covid). It adopted no standalone energy code: one- and two-family dwellings are permitted to comply through Sections N1101 and N1102 of the International Residential Code instead. The number the County actually enforces on a replacement window is the one written into its own permit-exemption text — U-0.34.

0.34 is the County’s own published figure, taken from the condition it attaches to the window permit exemption rather than from an IECC table.

For comparison, ENERGY STAR asks for U-0.25 or lower with an SHGC of 0.40 or lower everywhere in this metro, which is stricter than every code edition in force here. And the code only bites when the sash and the glazing are replaced together — replace the glass alone in an existing sash, or add a storm window over the top, and it does not apply.

Contractor registration No

St. Louis County licenses mechanical, electrical and plumbing contractors and nothing else. There is no general contractor category and no siding or window category, so a siding or window company can pull a County permit with no County trade licence at all. Individual municipalities may still require their own business licence.