🏠 Accessory Dwelling Unit (ADU) in Washtenaw County, Michigan
A secondary, self-contained living unit on a single-family lot — detached, attached, or conversion of existing space (garage/basement). Here is the Washtenaw County, Michigan picture: who issues the permit (county vs. city), the Michigan rule at a glance, a modeled local cost estimate, and the official sources to verify before you build.
Accessory Dwelling Unit (ADU) permit in Washtenaw County, Michigan
The Michigan rule for a accessory dwelling unit (adu), with fee range, timeline, go / no-go, and the official source. Whether the county or your city issues it depends on incorporation status.
Michigan
🏠 Accessory Dwelling Unit (ADU)
Exact permit fees are set by the local building department. WikEst shows the published or code-based range where one exists, linked to its official source — verify the final amount at the source before budgeting.
🏠 Accessory Dwelling Unit (ADU) permit fee in Michigan
Permit requiredGenerally allowedcity authority
Permit fee range
Building permit based on project valuation; verify with the city. Detroit issues residential permits in about 5 days.
Typical timeline
Typically 5–15 business days; Detroit ~5 days, Grand Rapids 5–10 days for simple projects.
Setback
Follow local zoning setbacks and lot-coverage limits; confirm with the city planning department.
Exempt if
No state size exemption for an ADU (it is habitable space).
Exempt criteria: None — ADUs always require a building permit and zoning approval.
ADUs are allowed in Michigan subject to local zoning. A building permit and zoning approval are required; some cities cap size and occupant/rental rules. Confirm with Detroit or Grand Rapids planning.
Official sources: Michigan LARA — Bureau of Construction Codes (2015 Michigan Residential Code) · City of Detroit — Do I Need a Building or Trade Permit? · City of Grand Rapids — Apply for a Residential Building Permit
Representative cities for Michigan: Detroit, Grand Rapids.
All 20 project fee ranges in Michigan
Official-source ranges where published; “By local jurisdiction” means no flat fee is published and the amount is set case by case.
| Project | Permit? | Authority | Fee range | Go / no-go |
|---|---|---|---|---|
| 🏠 Accessory Dwelling Unit (ADU) | yes | city | Building permit based on project valuation; verify with the city. Detroit issues residential permits in about 5 days. | allowed |
| 🪵 Deck / Porch | conditional | city | Valuation-based building permit; verify with the city. | allowed |
| 🧱 Fence / Wall | conditional | city | Typically a zoning/building permit fee; verify with the city. | allowed |
| 🛖 Shed / Outbuilding | conditional | city | Valuation-based where required; structures <200 sq ft often use a lower-compliance permit. | allowed |
| 🪜 Basement Finish | yes | city | Valuation-based building permit; verify with the city. | allowed |
| 🚗 Garage / Carport | yes | city | Valuation-based building permit; verify with the city. | allowed |
| ☀️ Rooftop Solar PV | yes | city | Electrical (and structural) permit per city schedule; verify locally. | allowed |
| 🌡️ HVAC Replacement | yes | city | Mechanical permit fee per city schedule; verify locally. | allowed |
| 🍳 Kitchen Remodel | yes | city | Building + trade permits based on valuation; verify with the city. | allowed |
| 🛁 Bathroom Remodel | yes | city | Building + trade permits based on valuation; verify with the city. | allowed |
| 🏗️ Room Addition | yes | city | Building permit based on valuation plus trade permits; verify with the city. | allowed |
| 🪟 Window / Door Replacement | conditional | city | Building permit (alteration) where required; verify with the city. | allowed |
| 🏘️ Roof Replacement | yes | city | Building permit (re-roof) per city schedule; verify locally. | allowed |
| 🅿️ Driveway / Parking Pad | conditional | city | Permit fee where required; verify locally. | allowed |
| 🏊 Swimming Pool / Spa | conditional | city | Building + electrical permit per city schedule; verify locally. | allowed |
| 🧱 Retaining Wall | conditional | city | Building permit where required; verify with the city. | allowed |
| 💥 Demolition / Teardown | yes | city | Demolition permit fee set by the city/county building department; verify locally. | allowed |
| 🚰 Septic System | yes | county | Septic permit fees set by the local health department; verify locally. | allowed |
| 🔌 EV Charger | conditional | city | Electrical permit fee set by the municipality; verify locally. | allowed |
| ⚡ Standby Generator | yes | city | Electrical (and often mechanical/gas) permit fee set by the municipality; verify locally. | allowed |
Michigan rule at a glance
Needs permit
yes
Issuing authority
city
Typical fee
Building permit based on project valuation; verify with the city. Detroit issues residential permits in about 5 days.
Typical timeline
Typically 5–15 business days; Detroit ~5 days, Grand Rapids 5–10 days for simple projects.
Setback
Follow local zoning setbacks and lot-coverage limits; confirm with the city planning department.
Exempt if
No state size exemption for an ADU (it is habitable space).
ADUs are allowed in Michigan subject to local zoning. A building permit and zoning approval are required; some cities cap size and occupant/rental rules. Confirm with Detroit or Grand Rapids planning.
County + cities (mixed)
Washtenaw County Building Inspection
Washtenaw County Building Inspection enforces the State Construction Code and issues building and trade permits for unincorporated areas and for participating jurisdictions (Augusta Township, City of Dexter, Lodi, Saline, Scio, Sharon, and Webster Townships). The City of Ann Arbor, City of Ypsilanti, Ypsilanti Township, Pittsfield Township, and other larger municipalities run their own building departments — check which office covers your address before applying.
Modeled cost estimate — accessory dwelling unit (adu) in Washtenaw County, Michigan
Statewide typical total: $90,000–$320,000 · ≈ $220 / sq ft
Modeled estimate. This band is the citable Michigan statewide contractor cost range (industry estimate, retrieved 2026-08-23). A per-county cost-of-living index (U.S. Census Bureau ACS) was not refreshed in this build (retrieval date 2026-08-29), so this page shows the statewide baseline rather than a county-specific figure. Local labor and material markets commonly shift a specific bid ±15–25% from the statewide median (industry observation, HomeAdvisor / Fixr). Always collect 2–3 written quotes from licensed local contractors before committing.
Frequently asked questions
Does a accessory dwelling unit (adu) need a permit in Washtenaw County, Michigan?
Washtenaw County follows Michigan state permit law. Whether the project needs a permit, and the fee, depends on size and scope — see the Michigan rule at a glance below, then confirm with Washtenaw County Building Inspection.
Who issues the accessory dwelling unit (adu) permit in Washtenaw County — the county or my city?
Permitting is split — cities issue for incorporated areas, the county for unincorporated areas. The permitting authority is Washtenaw County Building Inspection.
How much does a accessory dwelling unit (adu) cost in Washtenaw County, Michigan?
WikEst shows the citable Michigan statewide contractor cost band below (industry estimate, retrieved 2026-08-23). A per-county cost-of-living index was not refreshed in this build (retrieval 2026-08-29); local labor and material markets commonly shift a specific bid ±15–25% from the statewide median. Collect 2–3 written quotes from licensed local contractors.
How do I apply for a accessory dwelling unit (adu) permit in Washtenaw County?
Start at the official portal for Washtenaw County Building Inspection (linked above). Most offices accept online submissions; have your plans, site information, and contractor details ready before applying.
🏛️ Who issues permits in Washtenaw County?
The official Washtenaw County permit authority, portal, and county-vs-city split.
📊 Accessory Dwelling Unit (ADU) in all Michigan
The full Michigan accessory dwelling unit (adu) permit rule and fees.
Other counties in Michigan — Accessory Dwelling Unit (ADU)
Accessory Dwelling Unit (ADU) in other states
Michigan permit cheat-sheet
| Project | Permit? | Authority | Typical fee | Timeline | Go / No-Go | Key notes |
|---|---|---|---|---|---|---|
| 🏠 Accessory Dwelling Unit (ADU) | Permit required | city | Building permit based on project valuation; verify with the city. Detroit issues residential permits in about 5 days. | Typically 5–15 business days; Detroit ~5 days, Grand Rapids 5–10 days for simple projects. | Generally allowed | ADUs are allowed in Michigan subject to local zoning. A building permit and zoning approval are required; some cities cap size and occupant/rental rules. Confirm with Detroit or Grand Rapids planning. Exempt: No state size exemption for an ADU (it is habitable space). |
| 🪵 Deck / Porch | Conditional | city | Valuation-based building permit; verify with the city. | Typically 5–15 business days; Detroit ~5 days. | Generally allowed | Footings must extend below the frost line — 42 in in the Detroit/Grand Rapids area. Guards required at 30 in+ above grade. Verify setback and lot coverage with the city. Exempt: State R105.2 exempts decks ≤200 sq ft, ≤30 in above grade, not attached, not within 36 in of the dwelling, and not serving egress. |
| 🧱 Fence / Wall | Conditional | city | Typically a zoning/building permit fee; verify with the city. | Often issued in days to 1–2 weeks. | Generally allowed | Michigan exempts fences up to 7 ft under the state code, but cities set their own height/yard limits and may require a zoning review. Always check local ordinance and HOA. Exempt: State R105.2 exempts fences 7 ft high or less (Detroit: 7 ft or less, not in a Special Review District). |
| 🛖 Shed / Outbuilding | Conditional | city | Valuation-based where required; structures <200 sq ft often use a lower-compliance permit. | Often 5–10 business days; smaller sheds may be issued faster. | Generally allowed | Small detached storage sheds are usually exempt, but adding electricity/plumbing or exceeding 200 sq ft triggers a permit. Confirm setbacks with the city. Exempt: State R105.2 exempts one-story detached accessory structures ≤200 sq ft. Grand Rapids: <200 sq ft = Planning Accessory Structure Permit; ≥200 sq ft = building permit. |
| 🪜 Basement Finish | Permit required | city | Valuation-based building permit; verify with the city. | Plan review typically 2–4 weeks plus inspections. | Generally allowed | Converting a basement to living space requires permits for framing, egress, electrical, plumbing, and mechanical. Egress windows are required for bedrooms. Exempt: n/a |
| 🚗 Garage / Carport | Permit required | city | Valuation-based building permit; verify with the city. | Plan review typically 2–4 weeks plus inspections. | Generally allowed | New detached or attached garages and carports require a building permit and zoning/setback review. Exempt: Detroit exempts detached accessory structures ≤200 sq ft; new garages over that need a permit. |
| ☀️ Rooftop Solar PV | Permit required | city | Electrical (and structural) permit per city schedule; verify locally. | Often 1–3 weeks; some jurisdictions expedite residential PV. | Generally allowed | Residential rooftop solar PV requires an electrical (and often structural/mechanical) permit plus utility interconnection approval. Exempt: Any grid-tied rooftop PV system requires a permit. |
| 🌡️ HVAC Replacement | Permit required | city | Mechanical permit fee per city schedule; verify locally. | Usually 1–2 weeks; light plan review, straightforward inspection. | Generally allowed | Replacing or upgrading HVAC equipment requires a mechanical permit and inspection before energizing. Exempt: Any furnace, AC, or heat-pump replacement/installation requires a permit. |
| 🍳 Kitchen Remodel | Permit required | city | Building + trade permits based on valuation; verify with the city. | Plan review typically 2–4 weeks plus trade inspections. | Generally allowed | Kitchen remodels moving plumbing/electrical or altering walls require building, plumbing, and electrical permits. Exempt: Any layout/plumbing/electrical change requires a permit. |
| 🛁 Bathroom Remodel | Permit required | city | Building + trade permits based on valuation; verify with the city. | Plan review typically 1–3 weeks plus trade inspections. | Generally allowed | Bathroom remodels that move fixtures, add ventilation, or alter plumbing/electrical require permits. Exempt: Any fixture relocation or new wet wall requires a permit. |
| 🏗️ Room Addition | Permit required | city | Building permit based on valuation plus trade permits; verify with the city. | Plan review typically 3–6 weeks plus multiple inspections. | Generally allowed | Room additions change the footprint and require foundation, framing, egress, and trade reviews. Historic districts need a Certificate of Appropriateness. Exempt: Any new conditioned square footage requires a full permit. |
| 🪟 Window / Door Replacement | Conditional | city | Building permit (alteration) where required; verify with the city. | Often 1–2 weeks; many window jobs are issued without plan review. | Generally allowed | Replacing windows/doors in the same opening is typically exempt; enlarging an opening or cutting a new one requires a permit. Exempt: In-kind replacement in the same opening is often exempt. |
| 🏘️ Roof Replacement | Permit required | city | Building permit (re-roof) per city schedule; verify locally. | Often 1–2 weeks; inspection after decking/underlayment and after shingles. | Generally allowed | Detroit requires a permit for roof replacement. Other jurisdictions vary — verify locally before starting. Exempt: Detroit requires a permit for roof replacement (removal of substantial shingles). |
| 🅿️ Driveway / Parking Pad | Conditional | city | Permit fee where required; verify locally. | Often 1–2 weeks; right-of-way review can add time. | Generally allowed | New or widened driveways, curb cuts, and right-of-way work typically require a permit and possibly stormwater review. Exempt: State R105.2 exempts sidewalks/driveways ≤30 in above adjacent grade and not over a basement. |
| 🏊 Swimming Pool / Spa | Conditional | city | Building + electrical permit per city schedule; verify locally. | Plan review typically 2–4 weeks plus inspections. | Generally allowed | Pools require a building permit and code-compliant barrier (self-closing/self-latching gate). Electrical permit for wiring. Exempt: State R105.2 exempts prefab pools <24 in deep, ≤5,000 gal, installed entirely above ground. |
| 🧱 Retaining Wall | Conditional | city | Building permit where required; verify with the city. | 1–3 weeks; walls over threshold may need engineered drawings. | Generally allowed | Retaining walls holding more than 4 ft of fill require a permit and often professional design. Check HOA and drainage too. Exempt: State R105.2 exempts retaining walls ≤4 ft measured from bottom of footing to top (unless supporting a surcharge). |
| 💥 Demolition / Teardown | Permit required | city | Demolition permit fee set by the city/county building department; verify locally. | — | Generally allowed | A full teardown or major strip-out requires a demolition (building) permit from the city or county building department under the Michigan Residential Code. Demolition permits commonly require utility disconnects and, for older homes, asbestos/lead clearance before work begins. Detroit issues through its permits office. |
| 🚰 Septic System | Permit required | county | Septic permit fees set by the local health department; verify locally. | — | Generally allowed | New or replacement onsite wastewater (septic) systems require a construction permit from the local county health department under the Michigan Public Health Code. EGLE provides statewide oversight; engineered design and a site/soil evaluation are required. |
| 🔌 EV Charger | Conditional | city | Electrical permit fee set by the municipality; verify locally. | — | Generally allowed | A home EV charging station needs an electrical permit (dedicated 240V circuit and wall unit) issued by the municipality under the Michigan Residential Code. Michigan has no single statewide EV-permitting fast-track, so review time varies by city. Work must meet the NEC. |
| ⚡ Standby Generator | Permit required | city | Electrical (and often mechanical/gas) permit fee set by the municipality; verify locally. | — | Generally allowed | A permanently installed standby generator with a transfer switch and fuel (gas/propane) line requires electrical and often mechanical/gas permits, plus inspection. Setback, noise, and carbon-monoxide rules may apply, and HOAs may restrict installation. Verify with the municipality (e.g., Detroit or Grand Rapids). |