Free written scope consultation - allowances, timeline, and change-order rules on paper before a single trade is scheduled
Boxabl Home Additions & ADU: The San Antonio Owner’s Guide
If you own a Boxabl home in San Antonio and the addition or ADU portion of your setup is failing, you need a straight answer: a full Boxabl home addition or ADU project in San Antonio typically runs $45,000 to $130,000 installed, depending on scope, site work, and finishes. We stock and install Boxabl-compatible home additions and ADU components, and we can usually get a crew out to assess your situation within a few days. Most San Antonio owners discover a problem when a door stops sealing, a wall panel shifts, or the HVAC connection to the addition stops holding temperature.
We’re Mason Remodeling Co San Antonio, and we’ve been doing general contracting and whole-home work since 2004. We’re an independent service provider, not affiliated with Boxabl, which means we give you honest assessments without a factory script. Isaac Pruett has spent two decades on projects across the Southwest, and he’s seen enough modular builds to know what holds up in Texas heat and what doesn’t.
Which Boxabl Models This Applies To
Boxabl’s Casita line, and its expansion modules, all share the same structural DNA: steel-framed panels, foam insulation, and laminated interior surfaces. The home addition and ADU work we do applies to any Boxabl unit that’s been expanded or connected to a secondary module, regardless of whether yours is the standard Casita or a custom configuration. The compatibility gotcha most San Antonio owners don’t know: Boxabl panel connection points are drilled for specific bolt patterns that vary by production year, and a 2022 wall panel won’t always mate cleanly with a 2024 addition module without an adapter plate.
To identify what you have, look for the serial label on the lower corner of the wall panel nearest the front door. It will list the manufacturing date and module code. That code matters more than the model name because Boxabl has quietly revised their panel dimensions twice since 2021. When we quote a San Antonio job, we always verify the production year before ordering parts. For most owners, a quality aftermarket panel or connector from our stock works just as well as OEM, but we’ll tell you when the factory part is genuinely the better call.
Styles & brands we work with
Signs Your Boxabl Home Additions & ADU Is Failing
- Gaps appearing at panel seams – Texas temperature swings make steel expand and contract. When the gap widens enough to see daylight, the connection bolts have loosened or the seal has failed. This is the earliest warning sign, and it’s the cheapest to fix if caught now.
- Doors or windows that drag or stick – The module has shifted on its foundation anchors. San Antonio’s clay soil moves with rain and drought cycles, and a shifted Boxabl puts pressure on openings that were square when it left the factory.
- Condensation or water staining on interior walls near the addition joint – The seam between the main unit and the addition is where water finds a way in. The flashing detail Boxabl ships is often undersized for our rainfall patterns, and we see this regularly in neighborhoods from Stone Oak to Alamo Ranch.
- HVAC can’t hold temperature in the addition room – The duct connector between modules is a known weak point. When it separates or crimps, the addition becomes a hotbox in July and a refrigerator in January.
- Floor feels springy or soft near the addition threshold – The subfloor connection between modules has worked loose, or moisture has compromised the structural layer. This one requires immediate attention, not a wait-and-see approach.
See the difference
Before
After
Before
After
Before
AfterReplacement Cost & What’s Included
In San Antonio, a Boxabl home addition or ADU project runs $45,000 to $130,000 installed. On the lower end, you’re looking at a single-room bump-out with basic finishes and minimal site work. The upper end includes a full ADU with kitchen and bath, utility connections, and foundation work. Here’s how the pricing breaks down:
- Home Addition (standard scope): $45,000 – $130,000
- ADU Construction (standalone or attached): $90,000 – $220,000
- Garage Conversion to living space: $30,000 – $80,000
- Kitchen within the addition: $14,000 – $45,000
- Bathroom within the addition: $9,000 – $28,000
Every quote we write includes all materials, labor, permits when required, and disposal. You get a written price before any work starts, and that number does not change mid-project unless you change the scope. We also provide a written guarantee covering our work for 365 days from the completion date. If something fails in that window, we return at no charge.
DIY or Call Us?
An owner can safely do a few things: check panel seams for visible gaps, test doors for drag, and look for water stains. Those observations help us quote faster. But panel connection work, foundation anchor adjustments, and seam re-sealing on a Boxabl are not weekend projects. The panels are under structural load, and the connection bolts are torqued to factory specifications that vary by production year. Over-torquing or using the wrong fastener compound creates a worse problem than the one you’re fixing. This work involves structural connections, and when those fail, the result can be serious. Call a trained professional for anything beyond inspection.
If you’re seeing any of the warning signs above, call us at (254) 269-5071. We’ll walk through what you’re seeing, help you decide if it’s urgent, and schedule a visit if it is.
FAQs
A properly installed and sealed Boxabl addition should last 25 to 40 years on the structural side, but the seam seals and connection gaskets typically need real attention every 8 to 12 years in San Antonio’s heat. The UV exposure and temperature cycling wear out elastomeric seals faster here than in most climates. If you’re budgeting long-term, plan on seam maintenance roughly twice a decade.
Yes, in many cases the panel itself is fine and the problem is the connection hardware or the seal, both of which are repairable for a fraction of full replacement cost. We only recommend full panel replacement when there’s structural damage, delamination, or water intrusion that has compromised the panel core. Get an assessment before you assume the worst.
A single-room addition usually takes 4 to 8 weeks from permits to final walkthrough, and a full ADU runs 8 to 16 weeks depending on scope and weather. San Antonio’s summer heat can slow exterior work, and we factor that into every timeline we quote. Call (254) 269-5071 for a project-specific schedule.
We keep common Boxabl-compatible connectors, seals, flashing, and panel anchor hardware in stock for the most frequent San Antonio failure points. For model-specific panels or OEM parts that changed between production years, we order direct and they typically arrive within one to two weeks. We also stock parts for KraftMaid, Cambria, and Silestone, so if your addition includes those finishes, we can often address everything in one visit.
Know who’s coming, know what it costs, know it’s covered, that’s the whole job before the job starts. Call (254) 269-5071 for a free estimate on your Boxabl home addition or ADU project in San Antonio.
Written by Isaac Pruett, Owner, Mason Remodeling Co San Antonio at Mason Remodeling Co San Antonio, serving San Antonio and nearby areas.
