Garage conversion
Turn an attached or detached garage into a legal, rentable ADU.
The walls, roof and slab are already there, so the work is mostly inside: closing in the garage door, insulating, and bringing in plumbing, power and heat. The guides don’t price attached and detached garages separately; HomeAdvisor notes an attached garage is usually the cheaper of the two to convert.
Typical scope
- ✓Slab check and any repairs
- ✓Garage door removed; new wall, window and entry
- ✓Insulation to code
- ✓Egress window in the bedroom
- ✓Bathroom and kitchen plumbing
- ✓Electrical and heating / cooling
- ✓Fire separation where the garage meets the house
- ✓Permits and impact fees
National cost guides
about $29,000–$67,000
This Old House 2026 price guide, $31,500–$73,200, adjusted ~8% lower for Twin Falls construction costs
Twin Falls ADU projects
$80,000–$150,000
Our published range for a legal, rentable ADU conversion
Why the gap? A legal, rentable ADU conversion typically adds fire separation, egress windows, insulation to code, separate or upgraded utilities, permits and impact fees, and design. The national guide figures often describe simpler conversions.
Timeline: 2–4 months of construction once permits are approved
Basement or interior space (junior ADU)
Convert a basement, bonus room or part of the house into a small unit of its own.
No new structure — the work is making an existing space livable and separate: a way in and out, light, dry floors and walls, and a kitchen and bathroom.
Typical scope
- ✓Egress window or door for sleeping rooms
- ✓Ceiling height check
- ✓Moisture control for floors and walls
- ✓Separate entrance
- ✓Kitchen and bathroom plumbing
- ✓Electrical, heating / cooling and ventilation
- ✓Fire and sound separation from the main house
National cost guide
about $37,000–$115,000
HomeAdvisor 2026, $40,000–$125,000 national, adjusted ~8% lower for Twin Falls
Timeline: Confirmed at your assessment
Above the garage
A new garage with an apartment on top — or living space added over a garage you have.
This is new construction: the garage has to carry a second floor, and the unit needs its own stairs, plumbing and power run up to it. A structural engineer is part of the job.
Typical scope
- ✓Structural engineering for the floor above
- ✓Exterior or interior stairs
- ✓Plumbing and electrical run to the upper floor
- ✓Insulation, heating / cooling
- ✓Roof and exterior to match the house
- ✓Permits and impact fees
National cost guide
$125–$200 per sq ft
Fixr 2025, national average
Timeline: Confirmed at your assessment
Attached addition
Build a new unit onto the side or back of your home.
A new foundation, walls and roof tied into your house, with its own entrance, kitchen and bathroom. It has to meet the setbacks for the main house and match its roof, siding and windows.
Typical scope
- ✓Foundation and framing
- ✓Tie-in to the existing roof and walls
- ✓Separate entrance
- ✓Kitchen and bathroom plumbing
- ✓Electrical, heating / cooling
- ✓Fire separation from the main house
- ✓Permits and impact fees
National cost guide
$80–$210 per sq ft
HomeAdvisor 2026, national average
Twin Falls ADU attached projects
$120,000–$250,000
Typical total, varies by size and complexity
Timeline: 3–5 months of construction once permits are approved
Shop, barn or outbuilding
Convert a detached shop, barn or other outbuilding into a home.
These vary more than anything else on this page — some have a slab and solid framing, others need nearly everything. Foundation, insulation, utilities and code upgrades all depend on what’s there.
Typical scope
- ✓Foundation and structure check
- ✓Insulation and new interior walls
- ✓Water, sewer and power brought to the building
- ✓Windows, egress and entry
- ✓Kitchen and bathroom
- ✓Permits and impact fees
Priced at your assessment
Too variable — and too little reliable cost data — to publish a range.
Timeline: Confirmed at your assessment