Unilock Home Additions & ADU Nationwide

Unilock Home Additions & ADU: The San Antonio Owner’s Guide

Unilock home additions and ADU construction in San Antonio typically run $45,000 to $130,000 for a standard addition, and $90,000 to $220,000 for a detached ADU with foundation, utilities, and finishes. That’s the honest range we quote from, and it reflects what we see across Alamo Heights, Stone Oak, and the older lots near King William where setbacks and soil shift the number. Most homeowners discover their “part” isn’t a single component at all, it’s a foundation that settled, a tie-in that leaked, or a roofline that never quite married the original structure the way the drawings promised. When that happens, the fix is rarely a patch. It’s a rework of the connection point, done properly, with the written price in hand before the first tool comes off the truck.

Call (432) 233-0976

Which Unilock Models This Applies To

Unilock is best known for its concrete paver and retaining wall systems, and when a home addition or ADU in San Antonio is built on or around Unilock hardscaping, the compatibility question is about the base, not the block. Unilock pavers come in distinct series: the Town Hall and Brussels lines run 60mm thick for pedestrian patios, while the Hollandstone and Courtstone lines at 80mm can carry light vehicle loads. If an addition sits over or adjacent to existing Unilock pavers, the paver depth, laying pattern, and whether the original install used a permeable or sand-set bed all determine what the new slab or foundation can tie into without cracking. We look for the stamped manufacturer code on the underside of a lifted paver, and we measure the actual thickness with a caliper, because San Antonio sun fades surface color and you can’t identify a paver by looks alone. Homeowners ask about OEM versus aftermarket, which for Unilock really means matching the existing paver manufacturer versus substituting a similar dimensional block from a local stone yard. For structural tie-ins and ADU foundation work, we spec the original Unilock product where the old surface stays visible. For buried base course or non-structural fill, a quality equivalent from a San Antonio supplier is usually fine and costs less, and we say so in the written estimate.

Signs Your Unilock Home Addition or ADU Is Failing

• Pavers sinking or heaving near the addition’s foundation line. This usually means the original subgrade wasn’t compacted in lifts before the pavers went down, or water is migrating under the edge where old meets new. We see it often on San Antonio’s clay-heavy soils, which swell after rain and shrink in summer.
• Hairline cracks running from the new slab into the adjacent paver field. The addition’s concrete is curing and pulling, or the footings are bearing on different soil density than the paver base. Left alone, the crack widens and the pavers start to split.
• Water pooling at the seam where the addition wall meets the old paver patio. This is a grading or flashing issue, not a paver issue, but it shows up as paver settlement. The fix is re-sloping the base and adding a proper drainage channel, not just replacing blocks.
• Paver color fading unevenly across the area where the addition’s roof overhang ends. The shaded section keeps color longer than the exposed section. It’s cosmetic, but it tells you the installation date predates the addition, and that patch or addition-related paver work was sourced from a different lot or manufacturer.
• Retaining wall blocks leaning outward near the ADU foundation. That’s lateral pressure from water-saturated soil behind the wall. In San Antonio, a sudden downpour can move a wall that looked fine for years, and it needs a drainage assessment before any paver or wall block gets reset.

Replacement Cost & What’s Included

For San Antonio homeowners, the numbers we quote break down like this: a home addition runs $45,000 to $130,000, a detached ADU $90,000 to $220,000, and a garage conversion $30,000 to $80,000. The spread exists because a 400-square-foot bedroom bump-out on a flat Stone Oak lot is a different job than a 900-square-foot ADU with a bathroom, kitchen, and separate utility service on a sloped King William parcel. Every written price names the specific Unilock products we’ll match or replace, the base material, the labor, and the warranty on our work. You sign that number before any work starts. It doesn’t grow after the crew arrives. The 365-Day Done Right Promise covers the whole project, so if a paver settles or a seam opens in that first year, we come back and make it right.

DIY or Call Us?

You can safely check a few things yourself: look for standing water at the addition’s edge, note where pavers have dipped or cracked, and photograph the area after a hard rain. What you shouldn’t do is lift a retaining wall cap, pull up a field of pavers, or dig near the foundation line without knowing where the gas, water, and electrical run. San Antonio’s clay soil and shifting seasons make guessing wrong expensive, and a retaining wall under load can move suddenly if you undercut it. If the sign is cosmetic, wait and watch it. If it’s structural, call (432) 233-0976 and we’ll walk the site, write the scope down, and give you a number before any work is scheduled.