Fast, Reliable Garage Conversion ADU Across San Antonio
A garage conversion ADU in San Antonio typically runs $140,000 to $230,000 all-in, drawings through final inspection, depending on whether you’re legalizing an existing casita or building from a bare slab. The schedule is driven by lead times on millwork, glass, and post-tension foundation engineering, not by how many crews show up. That’s why we put the price in writing before anything gets ordered. If you’re weighing a garage conversion in San Antonio, call Ellery ADU Studio at (971) 497-2402 and we’ll walk you through what your specific lot and structure actually allow.
We work inside Loop 410 and out to the north-side HOA belt. We know the difference between a 1950s masonry garage in Harlandale and a post-2000 tract-home garage in Alamo Ranch, because the permit path is entirely different. The Edwards Aquifer overlay changes what you can build. The owner-occupancy rule changes who you can rent to. We’ll tell you both before you spend a dollar on drawings.
Why Ellery ADU Studio Is San Antonio’s Preferred Garage Conversion ADU Company
Ellery ADU Studio has designed, permitted, and built 900+ ADUs since 2015, every one with a written price before work started and a documented photo record when work was complete. That includes garage conversions across San Antonio, from Prospect Hill to Highland Hills. Nadia Ellery founded the studio the year California’s ADU permitting landscape shifted, and the same discipline she built there applies here: the permit set is the product. Not an afterthought.
The one-contract design-build model matters in San Antonio because the designer-versus-builder blame gap is how garage conversions die in this city. A designer draws a detached garage conversion with a bathroom addition. The builder says the plumbing rough-in wasn’t in the drawings. The homeowner is stuck holding two contracts and no finished casita. We close that gap. One contract. One written price. Per Haven Standard Clause 1, the price is written before any work begins, and per Clause 5, the scope is locked at signing. No door-side upsells.
Our San Antonio clients also get the 365-Day Done Right Promise: if the finished ADU is not built to the permitted drawings, we make it right. In writing, before the project starts. Most of our San Antonio work comes from referrals inside the same neighborhoods: someone near Fort Sam Houston sees a permitted casita go up, asks who did it, and calls us. That’s the reputation we want.
Our Garage Conversion ADU Services in San Antonio
Detached Garage Conversion
Detached garage conversions are the core of our San Antonio work because the city’s older housing stock, particularly around Harlandale and Prospect Hill, has detached masonry garages sitting on generous lots. These are prime legalization candidates. The catch is the foundation. San Antonio’s shrink-swell clay and caliche soils respond aggressively to boom-bust rain cycles, and a garage slab poured in 1965 without post-tension engineering will crack and separate within a few seasons. We don’t build on hope. We assess the slab, and if it’s within range, we document it. If it isn’t, we re-pour with deep piers and post-tension design before any finish work begins.
Garage Partition & Bathroom Add
Sometimes you don’t want to convert the whole garage. You want a bathroom and a partition so the back half becomes a rentable casita and the front half stays storage or workshop. This is common in San Antonio’s West and South Sides, where the casita tradition runs deep and families are looking for a legal way to house parents or adult children. Partition work requires careful plumbing and HVAC planning, especially with the summer heat load. A 400 square foot ADU in San Antonio needs a properly sized dedicated mini-split. Tapping the main house’s HVAC almost always results in a comfort complaint by the first August.
Attached Garage Conversion
Attached garage conversions are the more constrained option because you’re working within the main structure’s roofline and foundation. In San Antonio’s post-2000 tract communities like Stone Oak and Alamo Ranch, the garage is often the only viable ADU candidate on the lot, but HOA covenants frequently prohibit ADUs outright. Before you spend money on drawings, we check the HOA rules and the Edwards Aquifer overlay. If you’re inside the Recharge or Contributing Zone, an attached conversion that adds a bathroom can push you over your impervious cover cap. That’s not a surprise we want you to find at permitting.
Carport Conversion
Carport conversions sit in a gray zone in San Antonio. If the carport was built with the house and appears on the original permit, converting it to a conditioned living space is often faster than a detached garage build. If it was added later without permits, you’re starting from zero. We see both cases regularly, especially near Fort Sam Houston where post-war housing went up fast and carports were common. The foundation is usually the weak point: carport slabs were rarely engineered for living space. We’ll tell you what the slab can carry before we draw a single wall.
Every garage conversion in San Antonio also carries the same underlying requirement: the permit set is what gets you through the City of San Antonio’s building review. Our studio handles that in-house as part of the single contract. You get the permit set, the written price, the photo record on every visit, and the written warranty. It’s all part of what we do under our Garage Conversion ADU service line.
What happens when you call
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A real person answersNo phone trees - you reach a local pro.
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You get an upfront price rangeHonest numbers before anyone is dispatched.
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A background-checked tech heads outLicensed & insured, dispatched right away.
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You approve before work beginsNothing starts until you say go.
Trusted Brands We Service in San Antonio
We specify and coordinate prefab and modular systems within the same single contract, including James Hardie, Abodu, and Cover. That matters in San Antonio because the high-end garage conversion tier here is driven by long-lead items: custom millwork, architectural glass, specialty finishes. We stock and source locally where it makes sense, and we coordinate delivery timelines with the permit schedule so the fixed price doesn’t move while cabinets are on order. If you’re building a casita near Alamo Heights or Terrell Hills, the schedule driver is materials, not labor. We plan for that from day one.
Common Garage Conversion ADU Problems We See in San Antonio Homes
- Edwards Aquifer impervious cover cap violations. Adding a bathroom and a covered patio to a garage conversion on a north-side lot can push you over the hard limit for the Recharge or Contributing Zone. The result is a stop-work order. We check the overlay before design starts.
- Foundation cracks from expansive clay and caliche. Garage slabs in San Antonio’s older neighborhoods were rarely poured with post-tension engineering. Corners crack within two seasons, doors jam, and millwork cabinets separate from walls. We fix this with deep piers and engineered slabs, not patching.
- Owner-occupancy permit failures. San Antonio requires the owner to live on site for an ADU permit. A garage conversion built for an investor fails final inspection when the property is tenant-occupied, forcing a tear-out of noncompliant plumbing. We verify this before you commit.
- HVAC undersizing for summer heat. The sustained 100°F+ days from July through September mean a converted garage cannot coast on the main house’s AC. A dedicated mini-split is not an upsell. It’s the difference between a rentable casita and a hotbox.
Pricing for Garage Conversion ADU in San Antonio, TX
A garage conversion ADU in San Antonio typically falls into these ranges, all-in with drawings, permits, and construction:
- Garage Partition & Bathroom Add: $70,000-$110,000
- Attached Garage Conversion: $120,000-$190,000
- Detached Garage Conversion (legalization of existing structure): $140,000-$230,000
- Detached Garage Conversion (new build on slab): $180,000-$280,000
What moves the number in San Antonio is the foundation work, the millwork and glass package, and whether the property sits inside an Edwards Aquifer zone that constrains the footprint. The price we write is the price you pay. Per Haven Standard Clause 1, you get a written price before any work begins, and per Clause 5, the scope is locked at signing. If you already have a written estimate from another builder, bring it in. We’ll give you a Free Second Opinion. Call (971) 497-2402.
We Also Serve Cities Near San Antonio
Our crews serve San Antonio and the surrounding corridor: Schertz, Cibolo, San Marcos, and Kyle. The permitting rules shift once you cross city lines, particularly around the Edwards Aquifer boundaries, so it’s worth a conversation about where your property actually falls. Dispatch and scheduling are coordinated from our San Antonio office, and crews work locally throughout the metro.
Serving San Antonio, TX - Our Local Coverage Area
We’re based in the San Antonio area and know this community well. Use the map below to see our service coverage - if you’re nearby, we can almost certainly help.
FAQs - Garage Conversion ADU in San Antonio
Yes, but you’ll need to legalize the structure first, and the foundation is the deciding factor. Harlandale’s 1950s garages are typically single-wythe concrete block or brick on slabs that were never engineered for living space. If the slab has heaved along the caliche seam, as many have, you’re looking at removal, deep piers, and a re-pour with post-tension engineering before any finish work. That work is line-itemed in your written price. Call (971) 497-2402 and we’ll assess what your specific garage needs.
It can. Properties inside the Edwards Aquifer Recharge or Contributing Zones face impervious cover caps that limit how much of your lot can be covered by buildings and paving. A garage conversion that adds a bathroom and a patio can push you over the cap, triggering a stop-work order. This restriction exists in San Antonio and not in peer Texas cities like Schertz or Cibolo, which changes the design calculus entirely. We check the overlay on your specific parcel before we draw anything.
Because San Antonio’s summer heat load is brutal, with sustained 100°F+ days and high humidity from July through September. A converted garage has a different thermal envelope than the main house, and the existing HVAC was sized for the original square footage. Tapping it means the converted space will be uncomfortable by the first August. A properly sized dedicated mini-split is the standard for a rentable or livable casita. We line-item it in the plan, not as a surprise add-on.
No, it doesn’t kill it, but it shapes who builds. San Antonio’s owner-occupancy requirement means the permit requires you to live in the main house while the ADU is rented. Contractors working the southwest side near Lackland AFB regularly find homeowners motivated by the military PCS rental cycle: a permitted casita rents quickly to transient Air Force families. But if you’re an investor planning to rent both units, the permit will fail. Call (971) 497-2402 to confirm your situation before you commit.
Materials. On the high-end tier, the schedule is set by long-lead items: custom millwork and cabinetry, architectural glass, and specialty finishes. Labor can be scheduled. A steel French door system or a custom cabinet package cannot be rushed without compromising the work. We lock the price in writing before ordering, per Haven Standard Clause 1, so the number doesn’t move while the millwork is on order. Call (971) 497-2402 for a written price on your project.
Written by Nadia Ellery, Owner at Ellery ADU Studio, serving San Antonio with design-build ADU services since 2015.