# Garage Conversion & ADU in Spicewood, TX: 2026 Costs

By the Home Remodel Pro team · published 2026-11-10 · Garage Conversion & ADU, Spicewood

In Spicewood, converting an existing attached garage into finished living space with a bathroom typically runs $75k–$130k, and a detached ADU of 500–800 square feet typically runs $175k–$350k once site work, utilities and finishes are counted. The spread comes down to three things: whether you are adding a bathroom or a full kitchen, how far water, sewer or septic and power have to travel, and what your lot does to the foundation and the driveway. Below is what the money buys, what the county and other reviewing offices look at out here, and how long the whole thing takes from first visit to final walkthrough.

## What a Spicewood garage conversion or ADU costs

Every number below is a typical range we work within. You get one fixed price in writing before demolition starts, and that price is built from a drawing set and a finish schedule — not a square-foot guess over the phone.

Attached garage conversions are the lower-cost path because the slab, walls and roof already exist. The cost lives in insulation, conditioned air, electrical, a new exterior wall where the garage door was, flooring over a slab that was never meant to be finished, and plumbing if you want a bathroom. Detached ADUs are a small house: foundation, framing, roof, exterior cladding, a utility run from the main house or a new connection, and a full kitchen and bath.

What moves a project up the range: a full kitchen instead of a kitchenette, a second plumbing fixture group far from existing lines, a slab that needs leveling or a new trench cut for drain lines, long utility runs across a wooded or sloped lot, standing-seam metal roofing to match a hill country main house, and higher-end windows for west-facing glass. What moves it down: keeping the plumbing to one wall, a kitchenette with a sink and undercounter appliances instead of a range and hood, stock or semi-custom cabinetry, and leaving the exterior envelope where it is.

- Garage conversion, office or flex room, no plumbing: $45k–$75k
- Garage conversion with a full bathroom and kitchenette: $75k–$130k
- Detached ADU, 400–600 sq ft, one bedroom: $175k–$260k
- Detached ADU, 600–900 sq ft, one to two bedrooms: $250k–$350k+
- Septic design and new or expanded system, when the reviewing office requires one: $12k–$30k
- Utility trenching, service upgrade and site work on a sloped Spicewood lot: $8k–$35k
- Permit, review and inspection fees: typically $1,500–$6,000 depending on the reviewing jurisdiction and scope

## What is different about this work in Spicewood

Spicewood sits west of Austin along the Colorado River and Lake Travis, and most of it is outside Austin city limits in unincorporated Travis or Burnet County. That changes the review path, and it changes what the site costs. We confirm which office reviews your project before we price it, and we handle the submittals either way.

Wastewater is the first question we ask on a Spicewood ADU. Many properties out here are on an on-site septic system rather than a sewer main, and adding a bedroom or a second dwelling can affect how that system is sized. A licensed site evaluator or engineer designs the system and the county environmental office decides what is approved — we are not the ones who make that call. We build the schedule and the fixed price around their determination, and we have that answer before you sign a construction contract, not after.

Water is the second. Some Spicewood homes are on a well, some on a water supply corporation line. A new dwelling unit may need its own meter or service, and that coordination takes lead time, so we start it during design rather than during framing.

The third is the lot itself. Spicewood lots are often sloped, rocky and tree-heavy. Rock excavation for footings and utility trenches is a real line item here, and driveway or parking access for a detached unit sometimes needs grading. Projects near the Highland Lakes may fall under additional watershed review — if yours does, we prepare and submit that package with the rest of the permit set.

Climate drives the specification. Full summers of west sun mean we spec Low-E glazing on west and south elevations, properly detailed insulation at the former garage ceiling and at any slab-on-grade perimeter, and a correctly sized HVAC system for the added load. An underinsulated converted garage in Spicewood is an uncomfortable room eleven months a year, and that is the single most common thing we are called to fix on somebody else's conversion.

## Permits, reviews and inspections

Permitting is our job, not yours. We prepare the drawings, the energy compliance documents and the septic or utility paperwork, submit them to the reviewing jurisdiction, answer their comments, and schedule every inspection through final.

Whether your Spicewood property is reviewed by Travis County, Burnet County, the City of Austin's extraterritorial processes, or a water quality authority depends on your exact address and the scope of work. We verify that in writing during design. The reviewing office decides what permits and approvals apply to your project and under what conditions a second dwelling unit can be occupied. If your HOA or deed restrictions have something to say about accessory buildings, rentals or exterior materials, we ask for those documents up front so the design does not have to be redrawn.

Anything involving framing changes, removing a wall, adding a large opening or supporting a new roof is reviewed by a licensed engineer, and the engineer's sealed detail plus the permit office's approval control what gets built. We do not make those judgements on site, and you should be wary of any contractor who does.

Inspections typically include foundation or slab preparation on a detached unit, rough framing, rough electrical, plumbing and mechanical, insulation, and a final. On septic work there are separate inspections tied to the approved design. We coordinate all of them and keep the trades sequenced so nobody is waiting on a sign-off that was never called in.

## A realistic timeline, in weeks

Design and permitting happen before demolition. That is why the construction calendar we hand you is the one we build to — the drawings are done, the fixtures are selected and ordered, and the approvals are in hand before a tool comes out of the truck.

Add it up and a Spicewood garage conversion usually runs 5 to 7 months from first visit to finished room. A detached ADU with new septic or utility work usually runs 9 to 14 months. We do not promise a start date at the first meeting; we give you one when the permit is issued and long-lead items are confirmed.

- Week 1: on-site visit, scope conversation, measurements, photos of the garage or the proposed ADU site
- Weeks 2–4: design agreement, floor plans, elevations, structural engineering where the design calls for it, and selections for cabinets, tile, fixtures and windows
- Weeks 4–8: septic evaluation and design where required, utility coordination, HOA submittal if applicable, and your fixed price in writing
- Weeks 8–20: permit submittal, review comments and issuance — timing depends entirely on the reviewing office's queue and on septic approval
- Construction, garage conversion: 8–14 weeks
- Construction, detached ADU: 16–28 weeks
- Final week: punch list walkthrough, final inspection sign-offs, warranty documents and appliance and fixture manuals handed over

## How our fixed-price design-build process works

One contract, one team. We do the design, the engineering coordination, the permitting and the construction, with our own in-house carpenters doing the framing, trim and cabinetry installation. That matters on a small building where the framing, the millwork and the finish all have to land within a quarter inch of each other.

You get a fixed price in writing before any work starts. It lists the scope, the allowances, the fixtures by model where they are selected, and the construction schedule. The price changes only if you change the scope, or if an approval condition from the reviewing office changes what has to be built — and either way you see the revised number and sign it before we proceed.

Our workmanship warranty runs five years. Financing is available if you would rather not pull the full amount from cash or an equity line, and we can walk you through what that looks like alongside the fixed price.

A note on ADUs built for rental income: build the kitchen and bath to the same standard as the main house. The difference between a kitchenette with a plastic sink and one with a proper counter, a disposal and real cabinetry shows up in every tenant conversation for the next ten years, and it is a few thousand dollars at build time.

## What to ask any contractor, and what to do next

Before you sign anything with anyone, get straight answers to these. The answers tell you more than the number at the bottom of the page.

When you are ready, have these ready for the first visit: your plat or survey, your septic records if you have them, any HOA or deed restriction documents, photos of the garage or the ADU site, and a rough idea of how the space will be used — guest suite, long-term rental, office, or housing for family. We will walk the site in Spicewood, tell you what the real constraints are, and put a design agreement in front of you before we put a price in front of you.

- Is the price fixed in writing before demolition, and what specifically would change it?
- Who prepares and submits the permit package, and who schedules the inspections?
- Who determines the septic requirement, and is that answer in hand before the construction contract is signed?
- Are the carpenters employees or day labor sourced per job?
- What is the workmanship warranty, in years, and what does it exclude?
- Which allowances are in the contract, and what fixtures and finishes do those allowances actually buy?
- What does the construction schedule look like week by week, and what long-lead items could move it?

## Spicewood homeowners also ask

### Can I turn my Spicewood garage into a rentable apartment?

Often yes, but it depends on your address. Whether a second dwelling unit can be permitted and occupied on your lot is decided by the reviewing jurisdiction — Travis County, Burnet County, or another authority depending on where you sit — along with your septic capacity and any deed restrictions or HOA rules on your property. We verify all of that during design, before you sign a construction contract, and we handle the permit submittals either way. Budget $75k–$130k for a conversion with a full bathroom and kitchenette.

### Is a detached ADU worth it compared with converting the garage?

It depends on what you are giving up. A garage conversion is $75k–$130k with a bath and kitchenette, but you lose covered parking and storage, which matters in hill country weather. A detached ADU at $175k–$350k keeps the garage, gives the occupant real separation, and is usually the better answer for long-term rental or multi-generational use. If you want both, some homeowners convert the garage and add a carport or detached garage later.

### How much does septic work add to a Spicewood ADU?

When the reviewing office requires a new or expanded on-site system, expect $12k–$30k including the licensed design, the evaluation and the installation. Some properties have existing capacity and need only a review; others need a full new system with a designated drain field area, which also affects where the ADU can sit on the lot. This is the first item we chase, because it affects both the price and the site plan.

### How long until I can actually move someone in?

Plan on 5 to 7 months total for a garage conversion and 9 to 14 months for a detached ADU with new septic or utility work, measured from the first site visit. Roughly half of that is design, engineering and permit review, which happen before demolition. Construction itself is 8 to 14 weeks on a conversion and 16 to 28 weeks on a detached unit. We give you a start date once the permit is issued, not before.

## Check it with Spicewood's own pages

Permit rules and fees change, and the office that issues the permit is the authority on them, not this guide.

- [Burnet County Development Services — OSSF and development permits](https://www.burnetcountytexas.org/1239/On-Site-Sewage-Facilities-OSSF-Developme)
- [Travis County Development Services — apply for a permit](https://www.traviscountytx.gov/tnr/development-services/apply-for-a-permit)

What a garage conversion or ADU in Austin involves: https://www.homeremodelpro.com/austin/garage-conversion-adu

## Get a free estimate

- Call (512) 601-5666 (Monday to Friday 8am–6pm and Saturday 9am–2pm); a project consultant calls back within one business hour.
- Request an estimate online: https://www.homeremodelpro.com/austin#quote
- 5-year workmanship warranty · one fixed price in writing · in-house carpenters · permits and inspections included

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Source: https://www.homeremodelpro.com/austin/blog/garage-conversion-and-adu-spicewood-guide · Home Remodel Pro Austin, TX