What is included
- Primary suite and bedroom additions
- Second story additions over existing homes
- Detached ADUs and guest houses
- Attached ADUs and garage apartments
- Sunrooms and enclosed porches
- Foundation, framing, roofing and tie in to the existing house
How much does an addition or ADU cost in Austin?
An addition or ADU in the Austin area typically costs $250–$450 per sq ft for a ground floor addition, $300–$500 per sq ft for a second story, and $175,000–$350,000 ($275–$450 per sq ft) for a detached ADU of about 550–800 sq ft, installed and before sales tax.
| Project | Typical range |
|---|---|
| Ground floor room addition | $250–$450 per sq ft |
| Second story addition | $300–$500 per sq ft |
| Detached ADU, stick built (about 550–800 sq ft) | $175,000–$350,000 ($275–$450 per sq ft) |
Ranges for full service work by Tier One Builds in the Austin metro: design help, permits, licensed trades and cleanup, installed, before sales tax. They are not quotes; your quote is free and based on your home.
What raises the price in the Austin area
- Rock excavation on Hill Country limestone for pools, footings and plumbing
- Engineered foundations on expansive clay east of I-35
- Moving plumbing in a slab, or upgrading an undersized electrical panel in an older home
- Impervious cover limits, protected trees and historic review that change the design
- Permit, utility and impact fees, which are largest for new units and new homes
Can I build an ADU in Austin?
On many residential lots, yes. The City of Austin's HOME code changes, which took effect in 2024, allow up to three housing units on most single family lots and reduced the minimum lot size. Parking minimums were removed citywide in 2023. Setbacks, impervious cover limits, height limits, trees and any deed restrictions or HOA rules still apply, so every lot needs checking. Suburban cities such as Round Rock, Pflugerville and Georgetown have their own ADU rules.
Building an addition on Austin soils
East of I-35 and across much of Pflugerville, Hutto, Manor and Taylor, the ground is expansive Blackland Prairie clay that swells when wet and shrinks in drought. A new foundation has to be engineered for it and tied to the existing slab correctly so the two parts of the house do not move differently. West of MoPac and in the Hill Country, shallow limestone can mean rock excavation for footings and utility trenches. We plan for both before pricing.
Impervious cover and the Edwards Aquifer
Parts of west Austin, Hays County and Williamson County sit over the Edwards Aquifer recharge and contributing zones, where impervious cover limits are tighter. An addition, a new driveway and a patio all count toward that limit, so we check the numbers early.
How your project runs
- Free consultationWe meet at your property, listen to what you want to change and look at the conditions that affect it: structure, soil, utilities, trees and the rules for your lot.
- Free quoteYou get a quote based on the scope we agreed, with the decisions that drive cost explained so you can adjust before anything is signed.
- Design and permitsDrawings, engineering and selections are finalized, and we submit the permits your city or county requires.
- BuildWe schedule every trade, order materials early, pass inspections and keep you updated at each phase.
- Final walkthroughWe walk the finished work with you, fix anything on the punch list and hand over the paperwork for your project.
Frequently asked questions
How much does an addition or ADU cost in Austin?
An addition or ADU in the Austin area typically costs $250–$450 per sq ft for a ground floor addition, $300–$500 per sq ft for a second story, and $175,000–$350,000 ($275–$450 per sq ft) for a detached ADU of about 550–800 sq ft, installed and before sales tax. Your quote is free.
How long does it take to build an ADU in Austin?
Plan on about 5 to 11 months for a detached ADU of about 550 to 800 sq ft, from the start of design to the final inspection: 1 to 2 months for design and engineering; 1 to 3 months for permits; and 3 to 6 months of construction. Permit comment rounds, rock or clay foundations, protected trees, floodplain, historic or HOA review, material lead times, utility work, weather and changes after construction starts can all add time. We give you a schedule with your quote.
How long does a room addition take in Austin?
Plan on about 4 to 9 months for a ground floor room addition, from the start of design to the final inspection: 1 to 2 months for design and engineering; 1 to 2 months for permits; and 2 to 5 months of construction. A second story addition takes about 7 to 13 months in total: 2 to 3 months of design and engineering, 1 to 3 months for permits and 4 to 7 months of construction. Permit comment rounds, rock or clay foundations, protected trees, floodplain, historic or HOA review, material lead times, utility work, weather and changes after construction starts can all add time. We give you a schedule with your quote.
Addition or ADU?
An addition grows the main house and is best when you want more room in daily living. A detached ADU gives separate living space, privacy and the option of rental income, and can be built with less disruption to the main house.
Do I need an architect?
Additions and ADUs need drawings for permit, and structural work needs an engineer. We can work with your architect or bring in the design and engineering help the project requires.
From our projects
A full gut renovation of a single story ranch home in north central Austin: an opened kitchen, a new primary bathroom built as an addition, a covered patio turned into a bedroom, and a new exterior. The finished home has four bedrooms and two bathrooms. Shown here as a design rendering. See the full project.
Permits
We pull the permits your project needs and schedule the inspections. To see what the city requires, read our home addition permit guide and ADU (additional dwelling unit) permit guide, with Austin review times, fees and the surrounding cities' portals.
Guides
- Do I Need a Permit to Remodel in Austin? A Plain Guide
- Clay, Limestone and Sand: How Austin Area Ground Changes Your Project
- Building an ADU in Austin Under the HOME Rules
- Adding Units to Austin Investment Property Under the HOME Rules
- Where Austin's Oldest and Most Rented Homes Are, by ZIP Code
Related services
Where we build
We offer room additions & adus across the greater Austin metro, including Austin, Round Rock, Cedar Park, Georgetown, Lakeway and Kyle. See all service areas.