Garage Conversion to ADU in Austin: Cost, Rules & Process (2026)

Why Garage Conversions Are the Fastest Path to an ADU

If you already have a garage, converting it into a livable ADU is typically the cheapest and fastest way to add a rental unit to your property. The structure already exists — you're mainly adding insulation, plumbing, and finishes.

Garage Conversion vs. New Build: Cost Comparison

Here's how the numbers stack up for a typical 400 sq ft unit:

• Garage conversion: $80,000 - $150,000 ($200-$375/sqft)
• New detached ADU: $125,000 - $200,000 ($250-$400/sqft)

Garage conversions save on foundation, framing, and roofing since those already exist. The savings range from 30-50% compared to a ground-up build.

Austin-Specific Rules for Garage Conversions

Parking Requirements: Gone

The biggest barrier to garage conversions used to be parking. If you converted your garage, you had to build a replacement parking space. Under the HOME Initiative, parking requirements for ADUs have been eliminated. You can convert your entire garage without replacing any parking.

Building Coverage Still Applies

Since your garage already exists as a structure, converting it to livable space doesn't change your building coverage calculation. This is a major advantage — you're working within your existing footprint.

Permits Required

You absolutely need permits for a garage conversion. This isn't a DIY weekend project. You're changing the occupancy type from "storage" to "residential," which triggers building code requirements for:

• Egress windows (minimum size for emergency exit)
• Ceiling height (minimum 7 feet for habitable rooms)
• Insulation (must meet current energy code)
• Plumbing (bathroom and kitchen rough-ins)
• Electrical (upgraded panel, GFCI outlets, smoke/CO detectors)
• HVAC (heating and cooling for the living space)

The Conversion Process Step by Step

1. Assess Your Garage

Not every garage is a good candidate. Check these deal-breakers first:

• Ceiling height: Need at least 7 feet (ideally 8+). Many older garages have low ceilings, and raising the roof adds significant cost.
• Foundation: Garage slabs are often thinner than house foundations and slope toward the door for drainage. You may need to level or pour a new slab.
• Sewer access: Is there a sewer line nearby? Running a new sewer lateral across your yard can cost $5,000-$15,000.

2. Design & Permit

Hire an architect or designer familiar with Austin garage conversions. They'll produce plans showing the new layout, electrical, plumbing, and HVAC. Submit to DSD for review (typically 4-8 weeks).

3. Construction (2-4 months)

• Frame interior walls and close the garage door opening (or replace with a wall and windows)
• Run plumbing for bathroom and kitchen
• Upgrade electrical panel and add circuits
• Install insulation, drywall, and flooring
• Add HVAC (mini-split systems are popular for conversions)
• Finish with kitchen, bathroom fixtures, and final touches

4. Final Inspection & CO

The city inspects the finished unit. Once it passes, you get a certificate of occupancy and can legally rent it out.

Common Mistakes to Avoid

• Skipping permits: Unpermitted conversions can't be legally rented, reduce your home's value, and create liability issues.
• Ignoring the slab: Garage floors aren't designed for living spaces. Address moisture, leveling, and insulation before finishing.
• Underestimating plumbing cost: If your garage is far from the main sewer line, plumbing can eat a large portion of your budget.
• Forgetting about the garage door: Replacing the garage door opening with a proper wall, window, and entry door costs $3,000-$8,000 but is essential for insulation and security.

Is a Garage Conversion Right for You?

If you have a detached garage with good ceiling height and sewer access nearby, a conversion is almost always the best first ADU project. It's lower cost, lower risk, and faster than a new build. Use our eligibility checker to verify your property's zoning and lot size first.