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Oldcastle Home Additions & ADU: The San Antonio Owner’s Guide
Home additions and ADU construction in San Antonio typically run $45,000 to $130,000 for a standard project, and the single biggest variable is how well the new structure ties into your existing foundation and roofline. If you own an Oldcastle product line home, you’re working with concrete-block or precast systems that behave differently than stick-frame construction when you cut into them for a doorway, a bump-out, or a full attached suite. Our crew has done enough of these in San Antonio to know exactly where the surprises hide, and we price the work so those surprises don’t end up on your final invoice.
Most homeowners don’t wake up thinking about their wall system. They notice something quieter first: hairline cracks running along mortar joints near a corner, a door that suddenly sticks in summer, or a room that never quite holds temperature. Those are the signals that the wall assembly is moving or breathing more than it should, and before you add square footage, you need someone who understands why.
Which Oldcastle Models This Applies To
Oldcastle’s residential footprint shows up most often in San Antonio as concrete masonry unit (CMU) exterior walls, precast lintels over windows and doors, and occasionally segmented retaining wall systems that double as foundation stem walls. The compatibility question is always the same: are you tying into hollow-core block or solid precast panel? That changes everything about how we anchor new framing, where we place a header, and what moisture barrier we spec before the first strap goes in.
Here’s a checkable gotcha we run into constantly: older Oldcastle block in San Antonio was laid with ungrouted cells every 4 feet, which means you can’t just drill and epoxy anchors wherever you like. We core-drill a test hole to verify cell alignment before committing to a connection detail. If you’re planning a second-story addition, this matters even more because the vertical rebar schedule determines whether your existing wall can carry the new load or needs a supplemental steel column. Aftermarket retrofit brackets exist, but for load-bearing connections on an Oldcastle assembly, we spec OEM-matched masonry anchors sized to the block’s actual web thickness, not whatever is cheapest at the supply house.
Mason Remodeling Co San Antonio is an independent contractor and not affiliated with Oldcastle. We do, however, stock the same specification-grade material families we use on every job, and for masonry work we order directly from the manufacturers that supply Oldcastle-compatible products to the Texas market.
Styles & brands we work with
Signs Your Oldcastle Home Additions & ADU Is Failing
- Stair-step cracking along mortar joints: This is the classic sign of differential settlement between the block and your slab. In San Antonio’s expansive clay soils, we see it most after a wet spring followed by a dry August. The wall isn’t collapsing; it’s telling you the footing moved.
- Doors or windows that bind seasonally: If your interior doors start dragging in July and loosen up in January, you’re watching thermal expansion push the block wall against the framed openings. A properly detailed addition includes expansion joints that absorb this movement instead of forcing it into your trim.
- Efflorescence (white chalky residue) on interior block faces: This means water is moving through the wall. In San Antonio, we find failed parapet caps and missing through-wall flashing on most older Oldcastle assemblies. Adding a room without fixing the moisture path first guarantees mold inside the new drywall within two years.
- Crumbling mortar at the base course: The bottom row of block sits directly on your slab or stem wall. If that mortar is turning to sand, water is wicking up from grade. Our fix involves cutting a horizontal moisture barrier, not just repointing the face.
- Sagging lintel above a window or door opening: Oldcastle precast lintels are tough, but undersized ones deflect over decades. If you see a dip in the mortar line directly above an opening, the lintel needs reinforcement before any addition hangs new load on that wall section.
Replacement Cost & What’s Included
For a full home addition in San Antonio, plan on $45,000 to $130,000 installed. That range covers everything from a 200-square-foot bump-out with minimal foundation work to a 600-square-foot primary suite with a bath. ADU construction runs higher, $90,000 to $220,000, because you’re adding separate utility connections, a meter, and usually a second electrical panel. Garage conversions sit between at $30,000 to $80,000 depending on whether the existing slab meets code for living space.
Every price we give is written, line-itemed, and delivered before any work starts. That’s not a promotion; it’s how Mason Remodeling has operated since 2004, and Isaac Pruett won’t waive it. The quote includes demolition, structural connections to your existing Oldcastle assembly, rough and finish carpentry, drywall, paint, and all permit fees. Electric, plumbing, and HVAC are itemized separately so you can see exactly where the money goes. We pull permits on every single addition and ADU, and we don’t ask for a change order to cover something we should have caught during the walkthrough.
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AfterDIY or Call Us?
You can safely do the detective work: inspect your exterior walls after a heavy rain, mark any cracks with a pencil and date, and watch whether they grow over a few months. If you’re handy, clean out clogged weep holes along the base course. But do not cut into an Oldcastle block wall yourself. Running a concrete saw through a load-bearing masonry wall without shoring the load above it is how ceilings come down, and the dust from cut block contains silica that requires a proper respirator and water suppression. This is structural work; it’s not a drywall patch.
If you’ve got a cracked lintel, a settling corner, or a wall that’s pulling away from the house, call us at (254) 269-5071. We’ll send someone out to look, tell you what’s actually wrong, and put the scope in writing so you know the number before you decide anything.
FAQs
A properly detailed addition on an Oldcastle block home should last 50 years or more in San Antonio, but the weak points are always the connection details, not the block itself. Mortar joints need repointing around the 30-year mark, and the flashing at the roofline tie-in is the first thing we replace when we open up an older addition. Call (254) 269-5071 and we’ll inspect your existing walls before quoting.
Yes, most settlement cracks can be stabilized with epoxy injection and supplemental steel, provided the underlying soil movement has stopped. If the footing is still dropping, repair is throwing money at a moving target. We assess soil conditions and crack activity before recommending either path. Call (254) 269-5071 for an honest read.
Most home additions run 10 to 16 weeks from permit issuance to final inspection; a full ADU typically takes 5 to 7 months including utility connections. Weather and permit review times affect the schedule, but we give you a written timeline with milestones before we start. Call (254) 269-5071 to discuss your specific project.
We stock the common masonry anchors, flashing systems, and waterproofing products compatible with Oldcastle CMU assemblies on our trucks, but structural components like lintels and tie-downs are ordered per job to match your exact wall dimensions. We also work with KraftMaid, Cambria, and Silestone for interior finish packages when your addition includes a kitchen or bath. Call (254) 269-5071 and we’ll confirm what’s on hand for your scope.
Call Mason Remodeling Co San Antonio
Know who’s coming, know what it costs, know it’s covered, that’s the whole job before the job starts. We don’t send a salesperson to your house. We send Isaac Pruett or one of our Threshold Verified crew members, and you’ll have their name and photo before they knock. The price is in writing before the first tool comes off the truck, and the work is guaranteed for 365 days from the completion date. If something isn’t right, we come back and make it right at no charge.
Call (254) 269-5071 to schedule your free estimate. A live person answers, day or night.
Written by Isaac Pruett, Owner, Mason Remodeling Co San Antonio at Mason Remodeling Co San Antonio, serving San Antonio and nearby areas.
