St. Louis County, MO Building Safety: Building Permits (2026)

1 casts a wide net: any owner or authorized agent who intends to construct, enlarge, alter, repair, move, demolish, or change the occupancy of a building or structure needs a permit before starting, and the same rule reaches paved parking lots other than those serving a single-family dwelling, new or relocated lot lines that affect an existing structure, and any electrical, gas, mechanical or plumbing system regulated by the code. 3 lets the official authorize an early start at the applicant's own risk. 2 lists the work that does not need a permit, though the exemption is narrow.

A one-story detached shed, playhouse or similar accessory structure is exempt only if its floor area stays at 120 square feet or under; movable cases, counters and similar fixtures are exempt only below 5 feet 9 inches in height; and ordinary finish work like painting, papering or installing cabinets and countertops never needed a permit in the first place. Every other item on the exemption list, covering fences, retaining walls, small pools and window awnings, carries its own separate size or height ceiling that this general permit section does not replace.

5 gives the work 180 days to start and requires it to stay active, with an automatic lapse if work is suspended for 180 days after it begins; the building official can grant one or more 180-day extensions on written request with justifiable cause. 2, and the county gives 14 days' written notice before destroying the plans on file.