Residential permit rules in Wisconsin
Representative cities: Milwaukee, Madison. Covers 16 common home projects.
| Project | Permit? | Authority | Typical fee | Timeline | Go / No-Go | Key notes |
|---|---|---|---|---|---|---|
| 🏠 Accessory Dwelling Unit (ADU) | Permit required | city | Permit fees set by each municipality — verify with the local building inspection department (Milwaukee DNS or Madison Building Inspection). | Varies by municipality — simple permits often same-day to ~2 weeks; full plan-review permits several weeks. | Case by case | ADUs require a building permit plus zoning/use approval. Wisconsin’s UDC (SPS 320-325) governs one- and two-family dwellings; local zoning controls whether an ADU is allowed on your lot. Verify with your municipal building inspection department. |
| 🪵 Deck / Porch | Conditional | city | Permit fees set by each municipality — verify with the local building inspection department. | Varies by municipality — over-the-counter/simple permits often same-day to ~2 weeks. | Generally allowed | Milwaukee and Madison require a permit for decks attached to the dwelling or over 30 in above grade; footings are inspected for frost depth. Exempt: Freestanding decks low to grade and not attached are generally exempt under the UDC; attached decks and decks over 30 in require a permit. |
| 🧱 Fence / Wall | Conditional | city | Usually no building permit under the height threshold; zoning setback/height rules apply. Verify locally. | Varies by municipality. | Generally allowed | Verify with your municipal building inspection department; historic/district design review may apply in some cities. |
| 🛖 Shed / Outbuilding | Conditional | city | No fee under the exemption; a permit fee applies if over the local threshold. | Varies by municipality. | Generally allowed | Because the UDC does not cover detached garages/accessory buildings, permit requirements are set locally. Verify with your municipal building inspection department. Exempt: Detached accessory buildings are NOT covered by the UDC, but municipalities may require a permit by ordinance; small sheds are often exempt. |
| 🪜 Basement Finish | Permit required | city | Building permit fee set by the municipality; trade permits billed separately. | Varies by municipality — typically several weeks for full plan review. | Generally allowed | Finishing a basement into habitable space requires permits for egress, framing, electrical, plumbing and mechanical work. The UDC covers alterations to dwellings built since June 1, 1980; state plumbing/electrical codes apply to all homes. A sleeping room needs an egress window. |
| 🚗 Garage / Carport | Conditional | city | Building permit fee set by the municipality if required by local ordinance. | Varies by municipality — typically several weeks for full plan review. | Generally allowed | Detached garages are NOT covered by the UDC (the state does not regulate them), but municipalities commonly require a building permit by ordinance. An attached garage is an addition to the dwelling and is covered by the UDC. Verify with your local building inspection department. |
| ☀️ Rooftop Solar PV | Permit required | city | Electrical/structural permit fee set by the municipality. | Varies by municipality — often expedited for residential PV. | Generally allowed | Rooftop solar PV requires an electrical and (if the structure is modified) building permit under the UDC. Some municipalities (e.g., Milwaukee) exempt residential solar PV that does not modify the structure — verify locally. |
| 🌡️ HVAC Replacement | Permit required | city | Mechanical permit fee set by the municipality. | Varies by municipality — often same-day to ~2 weeks. | Generally allowed | Furnace, AC or heat-pump replacement requires a mechanical permit (UDC SPS 323 / state HVAC code). |
| 🍳 Kitchen Remodel | Permit required | city | Building permit fee; trade permits (plumbing/electrical) billed separately. | Varies by municipality — typically several weeks for full plan review. | Generally allowed | A permit is required when relocating plumbing/electrical, moving walls, or changing fixtures. Cosmetic-only work (cabinets, counters, paint) may be exempt. |
| 🛁 Bathroom Remodel | Permit required | city | Building permit fee; trade permits (plumbing/electrical) billed separately. | Varies by municipality — typically several weeks for full plan review. | Generally allowed | A permit is required when relocating plumbing/electrical, moving walls, or changing fixtures. Cosmetic-only updates may be exempt. |
| 🏗️ Room Addition | Permit required | city | Building permit fee based on valuation; zoning and plan review apply. | Varies by municipality — typically several weeks for full plan review. | Generally allowed | Room additions change the footprint and require a full UDC building permit, zoning approval and usually a site plan. |
| 🪟 Window / Door Replacement | Conditional | city | Permit fee if changing the opening; in-kind swap is often exempt. | Varies by municipality — in-kind swaps often same-day. | Generally allowed | Swapping windows or exterior doors in the same opening is generally exempt; enlarging or adding openings requires a permit. |
| 🏘️ Roof Replacement | Conditional | city | Roof-covering permit fee set by the municipality; in-kind re-roof may be exempt. | Varies by municipality — in-kind re-roofs often same-day. | Generally allowed | Roof covering replacement is typically permitted; structural deck replacement triggers a full building permit. |
| 🅿️ Driveway / Parking Pad | Conditional | city | No building permit for private flatwork; a right-of-way/curb cut needs a separate permit. | Varies by municipality. | Generally allowed | A permit may be required for right-of-way/curb-cut work; verify with your municipal building inspection department. |
| 🏊 Swimming Pool / Spa | Permit required | city | Building permit fee; barrier fencing required by code. | Varies by municipality — typically several weeks. | Generally allowed | Pools need a permit and barrier fencing under the UDC. |
| 🧱 Retaining Wall | Conditional | city | No fee under the exemption; a permit applies if over the threshold. | Varies by municipality — if required, typically several weeks. | Generally allowed | Walls over 4 ft or supporting a surcharge require design and a permit. Verify with your municipal building inspection department. Exempt: Retaining walls ≤4 ft (not supporting a surcharge) are exempt (UDC references IRC R105.2). |