Garage-to-ADU Conversion Cost
Converting a garage into an ADU is more than enclosing a parking space. It creates an independent dwelling function, usually with a kitchen, bathroom, sleeping area, entrance, utilities, and a local approval path. Angi reports a 2026 US average of about $110,000 for this project and a broad conversion range, but the figure is a specialist market observation, not a legal or Canadian price.
What the existing shell saves—and does not
The garage may already provide walls and a roof, but those assemblies may not meet the intended living-space performance. Check slab elevation and condition, moisture, insulation, windows, roof, structure, fire or sound separation, and the relationship to the main home. A detached garage may need new underground water, sewer, and electrical routes; Angi reports a directional 20–30% increase for detached conversions in its source’s market observation.
The cost layers
- Plans and approvals: Design, structural review, zoning, permits, inspections, and any utility or address work.
- Shell: Garage-door infill, new windows or exits, insulation, air sealing, drywall, roof or exterior repairs, and floor work.
- Independent living: Kitchen cabinets and appliances, bathroom, hot water, heating and cooling, ventilation, lighting, and electrical distribution.
- Site and services: Trenching, meters or service work, sewer or septic capacity, drainage, parking, walkways, and restoration.
- Access and protection: Construction access, storage, temporary protection, demolition, disposal, and cleanup.
Attached versus detached
An attached garage may share services and a wall but can require careful separation, privacy, noise control, and entrance design. A detached garage may offer independence but often needs longer utility routes and more site restoration. Neither is automatically cheaper.
The legal boundary
An ADU is not a universal legal category. The 2024 IRC appendix gives a model-code example of internal, attached, or detached units with entrance, utilities, and scale conditions. CMHC and British Columbia guidance show Canadian terminology and frameworks vary. Confirm local zoning, parking, fire, egress, accessibility, dwelling classification, and rental rules before treating a conversion as permissible.
Quote comparison
Ask whether the proposal includes the kitchen, bathroom, HVAC, electrical, utility extensions, slab work, windows, entrance, separation, permits, design, parking, demolition, and restoration. Have the bidder identify what is assumed about the garage’s existing foundation, floor elevation, moisture, and capacity.
Compare the conversion with a detached ADU and ordinary garage-to-living-space conversion only after defining the intended independence. The garage creates a potential shortcut, not a guaranteed saving.
Existing conditions to verify
Check whether the garage floor is below the house, whether it has moisture or drainage issues, how the walls and roof are insulated, where services enter, and whether the shell can support the proposed use. A detached garage may need new underground services; an attached garage may need more separation and privacy work. A small shell correction can expose a larger building problem.
Independence changes every trade
The kitchen affects cabinets, appliances, plumbing, ventilation, electrical, and hot water. The bathroom affects drainage, waterproofing, ventilation, and finishes. A separate entrance affects doors, steps, weather protection, security, and sitework. Independent heating, metering, or services can add equipment and access requirements. Price these as visible layers.
Parking and use
Confirm what parking the property must retain and how vehicles, storage, tools, and deliveries will be handled after conversion. Local authorities may treat parking and dwelling status differently. A legal conversion in one place is not evidence of permission in another.
Compare conversion with new construction
Angi reports about $180,000 for new ADU construction in the same broad US market context as its garage-conversion observation. That is not a national or Canadian comparison. A detached new unit may cost more in foundation and sitework but avoid some garage-shell compromises. Price both scopes using the same independence and finish assumptions.
Do not approve a garage conversion until the owner knows what the existing shell saves, what it requires, and what the property loses.
Make the independence decision explicit
List the functions the occupant needs: sleeping, bathing, cooking, laundry, storage, entrance, parking, heating and cooling, and utility control. A shared family suite may need less independence than a separate dwelling. The difference affects the kitchen, entrance, services, separation, privacy, and approval work.
What happens after conversion
Ask who maintains the roof, exterior, heating and cooling, water heater, electrical equipment, drainage, and shared access. If systems are shared, decide how service and replacement costs are allocated. If systems are independent, include equipment, meters or controls where permitted, and service access.
A complete decision
Compare garage conversion, detached ADU, basement suite, and addition only after each has the same living function and finish quality. A shell saving is meaningful only if the resulting unit can be approved, connected, comfortable, and maintained for the intended occupant.
Attached and detached risk profiles
An attached conversion may have shorter service routes but can disturb the main home and require careful separation. A detached conversion may protect household privacy but require trenching, utility capacity, access, and site restoration. Compare the total project and the long-term service responsibility, not the garage shell alone.
Discovery before finish selection
Before selecting cabinets or flooring, confirm moisture, slab, structure, insulation, roof, entrances, utilities, parking, and classification. A finish package chosen before those gates are resolved may need to be removed or redesigned. The most useful early spend is the assessment that narrows the unknowns.
Determine whether the garage shell is reusable
Separate what the garage already provides from what an independent dwelling needs. The existing roof and walls may reduce some enclosure work, but the slab elevation, drainage, moisture history, insulation, windows, structure, and exterior openings still need review. A detached garage may need a long utility route; an attached garage may need more careful separation, privacy, sound, and service coordination with the main house.
Use a condition brief that records the garage’s form, dimensions, floor level, door openings, posts, utilities, access, and parking role. Ask a qualified professional to identify which conditions are verified and which could require correction. Do not infer that an existing garage is convertible because it is dry on one visit or because its shell looks sound.
Price independence as a bundle
An ADU conversion can require a kitchen, bathroom, sleeping area, independent entrance, heating and cooling, ventilation, electrical distribution, plumbing, windows or exits, and local life-safety or separation work. Site and utility work may include trenching, service upgrades, wastewater capacity, meters, drainage, parking, walkways, and restoration. Price these functions together when comparing an ADU with a detached unit; otherwise the garage shell can make the conversion look artificially cheap.
The model-code, provincial, and state examples in the source set show why these questions matter but do not establish local law. Confirm the intended dwelling classification, parking, entrance, egress, fire, accessibility, utilities, inspections, and rental treatment with the relevant authority. A policy or appraisal definition cannot replace that check.
Compare conversion with a new unit
Give the garage option a serviceability test after completion. Show where filters, shutoffs, panels, water heaters, and ventilation equipment can be reached without entering a private sleeping area. Confirm that deliveries, waste removal, and routine maintenance have a practical route. Independence that cannot be maintained without disturbing occupants is only partial independence.
If the new-unit option uses a different site location, include the main home’s remaining yard, parking, privacy, and service access in the comparison. A new shell may cost more while preserving a valuable garage, or it may create a longer utility route and more site work. Keep those property effects next to the building totals.
Use a matched brief for the two options. Include the same number of occupants, sleeping and living functions, kitchen and bathroom expectations, privacy, entry, storage, heating and cooling, and utility independence. Then add the work that is unique to the garage: slab or floor correction, insulation, new openings, ceiling height, fire or sound separation, and the loss of covered parking or storage.
The conversion deserves an early stop if its shell cannot support the intended result without extensive structural or moisture correction. In that case, do not continue refining cabinet or finish allowances. Compare a new unit or a different location using the evidence already gathered. A higher shell cost can be rational when it produces a cleaner service route, better access, and a result that remains adaptable.
For either path, list the boundary between building work and site work. Driveway changes, utility trenching, drainage, meters, exterior lighting, and restoration can sit outside a conversion quote while still being necessary for the ADU to operate. The winning option is the complete, permitted, serviceable property outcome.
Request a garage-conversion scenario, a detached or attached new-unit scenario, and an ordinary living-space conversion when the household’s independence needs are undecided. Use the same finished area and functional outcome. The conversion may save shell work while adding slab or envelope correction and utility constraints. New construction may cost more in building and site work while offering a cleaner plan, access route, and service layout.
Include the permanent consequences: lost parking or storage, maintenance access, shared utilities, resident privacy, and future repair routes. Proceed to detailed finishes only when the shell, independence, service path, approval path, and household use are clear.