Demilec Crawl Space Encapsulation: The San Antonio Owner’s Guide
Demilec crawl space encapsulation in San Antonio typically runs $4,500 to $9,800 installed for a standard 1,200 to 1,800 square foot crawl space, depending on liner thickness, access difficulty, and whether your existing vapor barrier needs full removal. We stock Demilec-compatible encapsulation materials in our San Antonio warehouse and can usually start within three to five business days of your written quote. Most homeowners discover they need this work after a musty smell drifts up through the floorboards, a higher-than-expected summer electric bill, or humidity readings in the crawl space topping 65% on a regular basis.
Which Demilec Models This Applies To
Demilec doesn’t sell one-size-fits-all encapsulation kits. Their crawl space system breaks down by liner thickness and adhesive chemistry, and matching the right product to your San Antonio crawl space matters more than most installers admit. The two workhorses are the Heatlok HFO line (closed-cell spray foam, used for rim joists and foundation walls) and the Demilec vapor barrier membranes, which come in 10-mil, 12-mil, and 20-mil reinforced grades. If your crawler has a white or silver liner stapled to the piers, you’re likely looking at a 10-mil barrier that was never meant to last more than a decade in Texas humidity.
What matters for replacement is this: Demilec spray foam bonds differently than open-cell alternatives. If your existing encapsulation uses Demilec Heatlok on the walls and a separate liner on the floor, the two products must be compatible at the seam, usually with a Demilec-specified tape or mastic. An aftermarket tape from a big-box store will peel within two San Antonio summers. We stock the OEM-compatible seam tapes and mastics, plus aftermarket liner options where they genuinely hold up. One compatibility gotcha we see regularly in San Antonio: crawl spaces vented to the outside before encapsulation usually have high mineral content in the soil, and that mineral dust prevents Demilec foam from adhering properly unless the foundation walls get a specific prep wash first. Skip the wash, and the foam delaminates within 18 months.
Signs Your Demilec Crawl Space Encapsulation Is Failing
- Humidity readings above 65% in the crawl space. A functioning Demilec encapsulation holds the space between 45% and 55% relative humidity. If your hygrometer sits higher, the liner or foam seal has failed somewhere, or the dehumidifier tied into the system isn’t keeping up.
- Visible sagging in the liner. When Demilec liners age past their useful life, they stretch and pull away from the pier anchors. Water pools in those low spots, and eventually the liner becomes a pond liner instead of a vapor barrier.
- Musty odor migrating into living areas. This is the symptom that gets the most calls in San Antonio. Once the encapsulation seal breaks, soil moisture releases that damp-earth smell, and your HVAC return pulls it straight into the house.
- Foam pulling away from the foundation walls. You’ll see gaps along the rim joist where Demilec Heatlok has shrunk or separated from the masonry. Those gaps let humid air pour in at exactly the points the encapsulation was supposed to seal.
- Higher cooling bills with no other explanation. A failed crawl space encapsulation means your AC is fighting 80-degree, 70% humidity air from below the house. San Antonio summers already push air conditioners hard; a broken seal adds hundreds of dollars to your annual cooling cost.
Replacement Cost & What’s Included
In San Antonio, full Demilec crawl space encapsulation replacement runs $4,500 to $9,800 for most homes. Smaller crawls under 800 square feet can land between $3,200 and $4,500. The price swings on three things: liner thickness (20-mil reinforced runs about $0.45 to $0.75 more per square foot than 12-mil), how much old material needs removal and disposal, and whether your rim joists need new spray foam or just seam repairs. Our quotes always separate materials from labor, so you see exactly what you’re paying for before we touch anything. Every Demilec encapsulation job we do in San Antonio includes seam taping with Demilec-compatible products, pier sealing, a 12-mil minimum liner (we recommend 20-mil for crawls with any history of water intrusion), and a written 365-Day Done Right Promise covering labor and materials. Liner and foam manufactured by Demilec carry their own manufacturer warranty, which we help you register.
DIY or Call Us?
You can absolutely do the diagnostic work yourself: check your humidity readings, look for visible liner sag, and run your hand along the rim joist to feel for foam separation. Those are safe checks, and knowing what you’re seeing makes you a smarter buyer when you call us. What you shouldn’t do is attempt Demilec spray foam application without proper training. Heatlok HLO cures at high temperature and expands fast; an amateur application in a confined crawl space is a respiratory and fire hazard, and the foam won’t bond correctly without the right substrate prep. Even liner replacement requires working on your back in tight quarters, cutting around piers, and sealing every seam perfectly. One missed seam and you’ve spent a weekend installing a very expensive plastic curtain that doesn’t stop moisture. If you want the safe version of DIY, take photos of what you’re seeing and text them to us before you call. We’ll tell you straight whether it’s a repair or a full replacement. Call (361) 213-9499 and we’ll walk through it with you.
FAQs
In San Antonio’s climate, a properly installed Demilec encapsulation system typically lasts 15 to 20 years for the liner and 20+ years for the spray foam, though the dehumidifier component usually needs replacement every 5 to 8 years. The biggest killer of encapsulation in this area isn’t age, it’s foundation movement and poor initial seam work. If your liner is failing before year ten, it was either installed incorrectly or it’s a thinner grade than the job required. Call (361) 213-9499 and we’ll inspect it and give you a straight answer on remaining lifespan.
Yes, in many cases. If the failure is isolated to one or two seams, a loose pier seal, or a small tear in the liner, a proper repair with Demilec-compatible tape or mastic costs $200 to $600. If the liner itself is brittle, torn in multiple places, or the foam has delaminated across a significant portion of the foundation walls, replacement is the honest answer. We’ll always show you photos of what we found and explain why a repair will or won’t hold before recommending full replacement. Estimates are free.
Most San Antonio homes take one to two days for a full Demilec encapsulation replacement, assuming the old liner is removed on day one and the new liner, seams, and pier seals go in on day two. Larger crawls or jobs requiring full rim joist spray foam can add a third day. We’ll give you a written installation timeline with your quote, and the crew’s name and photo before they arrive.
We keep Demilec-compatible 12-mil and 20-mil liners, seam tapes, mastics, and Heatlok HFO foam in our San Antonio warehouse, so most jobs don’t wait on shipping. We also stock aftermarket liners from Reflectix and other brands where they match or exceed the Demilec spec. If your job requires a custom-cut liner or an unusual access setup, we order ahead and keep you posted on the timeline. Call (361) 213-9499 for a free estimate: we’ll quote you a specific price before any work begins, not a range that changes when the crew shows up.
Written by Garrett Sloane, Owner, Aspen Attic Insulation San Antonio, serving San Antonio and nearby areas. Garrett grew up in Los Angeles and learned the insulation trade at Los Angeles Trade-Technical College before running crews across the Southwest. He’s been working in San Antonio homes for over a decade, and he’ll tell you straight: if your attic’s cooking, your AC is drowning, let’s fix the cause, not just the bill.