Demilec Attic Insulation: The San Antonio Owner’s Guide
If you’ve got Demilec spray foam or injection foam in your San Antonio attic and it’s not performing like it used to, we stock and install Demilec-compatible attic insulation with most jobs priced between $1,800 and $4,200 depending on square footage and existing conditions. We can usually be in your attic within 24 to 48 hours to assess what’s failing and give you an exact number. Most homeowners don’t wake up thinking about their Demilec insulation. They notice the upstairs bedroom won’t hold temperature in August, or the electric bill jumped $60 a month, or there’s a musty smell coming from the attic hatch. Then they climb up, take a look, and realize something’s off: foam pulling away from rafters, bare spots, dust where there used to be a solid seal.
We’re Walt’s Insulation, and we’ve been working with Demilec products in San Antonio attics since the early 2000s. We’re an independent installer and service provider, not affiliated with Demilec directly. That means we tell you the truth about what’s failing and what it costs to fix, without a corporate script. Walt Brenner started this company in 2000 after seeing too many South Texas attics with foam that was never going to survive our heat, and we’ve spent 25 years fixing exactly those problems. We answer the phone live – talk to a real person, get a straight answer.
Which Demilec Models This Applies To
Demilec makes two main product families you’ll find in San Antonio attics: the Heatlok HFO and Heatlok Soya closed-cell spray foam lines, and the Sealection 500 open-cell line. There’s also Agribalance, their soy-based open-cell product that’s less common here but shows up in newer builds. The compatibility gotcha most owners miss is that Heatlok and Sealection are not interchangeable: closed-cell and open-cell foams have different R-values per inch (roughly R-6.5 to R-7 versus R-3.5 to R-4), different vapor permeability, and different structural properties. If someone patches Sealection with Heatlok or vice versa, you get uneven thermal performance and potential moisture issues at the seam.
How to identify what you have: look at the foam color and texture. Heatlok cures to a pale yellow or green, feels rigid, and you can’t press your thumb into it. Sealection cures white or off-white, feels spongy, and compresses when you push on it. The Demilec label is usually stapled to a rafter or truss near the access point. If the label’s gone, an installer can identify it in about 30 seconds by look and feel. We keep Heatlok HFO and Sealection 500 parts and materials on our trucks and can special-order the less common lines. For OEM versus aftermarket: Demilec doesn’t really have a “part” ecosystem like a furnace does; the product is the material itself. What fails is the application. We use genuine Demilec material when redoing Demilec work because matching foam chemistry matters for adhesion and long-term performance. We also stock Reflectix radiant barrier for attics where a reflective layer makes more sense than foam.
Signs Your Demilec Attic Insulation Is Failing
- Foam pulling away from rafters or decking. This means the foam delaminated from the substrate. In San Antonio, extreme attic heat cycling, usually 140°F-plus in July and August, causes expansion and contraction that weakens the bond over time. Once it separates, air moves behind the foam and it stops insulating.
- Bare spots or thin coverage. An installer who sprayed too thin, or missed spots around trusses and baffles, left you with thermal shorts. With closed-cell Heatlok, you need at least 2 inches for air sealing and 4-plus inches for a meaningful R-value. We regularly find attics in the Alamo Heights and Terrell Hills areas where coverage runs 1 inch or less in spots.
- A musty or chemical smell from the attic. Properly cured Demilec foam has almost no odor. A persistent smell suggests the foam was sprayed too thick in one pass, trapped uncured material underneath, or has begun to degrade. This is a bigger problem in San Antonio’s humidity when the attic isn’t ventilated well enough before spraying.
- Upstairs rooms that can’t hold temperature. When your AC runs nonstop from June through September and the upstairs is still 8 to 10 degrees warmer than the thermostat setting, your Demilec insulation has likely lost its seal somewhere. Foam is an air barrier as much as insulation; small gaps defeat it.
- Dust or crumbling at floor level. Open-cell Sealection can degrade and shed particles when it’s been exposed to UV light through a roof leak or ridge vent gap. If you’re finding yellowish dust on attic stored items, the foam is breaking down and needs attention.
Replacement Cost & What’s Included
In San Antonio, repairing or replacing failing Demilec attic insulation runs $1,800 to $4,200 for most homes, with larger attics above 2,000 square feet running higher. The range depends on three things: how much existing foam has to be removed, whether you’re doing a spot repair or a full respray, and which Demilec line we’re using. Spot repairs where foam has delaminated from a section of rafters typically run $800 to $1,500. Full removal and respray of a 1,500-square-foot attic with open-cell Sealection 500 usually lands around $2,800 to $3,600. Closed-cell Heatlok HFO full respray runs higher, $3,500 to $5,000, because the material costs more per board foot.
Every quote includes removal of failed material where needed, prep and masking, new Demilec foam, cleanup, and our lifetime workmanship guarantee under the Done Right Promise. If it’s not done right, we make it right – no runaround, no fine print. We also offer a free second opinion on any written estimate you’ve received from another San Antonio contractor. And we never charge a trip fee inside our service county, so getting us out to quote costs you nothing. Standing offer: $40 off any repair over $200. Seniors and veterans always get 10% off, permanently.
DIY or Call Us?
You can safely do one thing: look. Shine a flashlight across your attic, note where the foam is pulling away, measure roughly the square footage of bare spots, and check for moisture stains. That tells you the scope. What you should not do is attempt to respray or patch Demilec foam yourself. Spray foam is a two-component chemical reaction that happens under pressure; incorrect mixing creates a mess that is extremely difficult to remove and can leave uncured chemical residue in your attic air. Uncured isocyanate is a genuine respiratory hazard. You also need proper PPE including a full-face respirator, which most homeowners don’t have on hand.
What we see in San Antonio when DIY foam repair goes wrong is an attic floor, trusses, and stored items coated in a sticky, rock-hard layer that costs triple to remediate than the original fix would have. If you’ve got failing Demilec insulation, call (866) 751-4428 and we’ll assess it honestly. We’re the one down the road, not an 800 number in another state.
FAQs
Properly installed Demilec spray foam lasts 30 to 50 years in a San Antonio attic. The catch is “properly installed.” Our heat plus the movement of roof decking over decades can delaminate foam that was sprayed in poor conditions or at the wrong thickness. We’ve seen Demilec foam fail in 8 to 12 years when it was sprayed on damp wood or in a single overly thick pass. If yours is pulling away, give us a call at (866) 751-4428 and we’ll tell you if it’s worth saving.
Yes, spot repairs are usually possible when the delamination is confined to one or two sections and the remaining foam is still well-adhered. We cut out the failed section, prep the surface, and respray with the matching Demilec material. If more than about 30% of the attic shows separation, full removal and respray is usually cheaper per square foot and gives you a clean thermal envelope. Estimates are free.
Most Demilec spot repairs take 3 to 4 hours including prep and cleanup. A full attic removal and respray typically runs one full day for open-cell and can stretch into a second morning for closed-cell Heatlok in larger San Antonio homes. We’ll give you a clear timeline in the quote before you commit.
We keep Heatlok HFO, Sealection 500, and the necessary application equipment on our trucks year-round. That means we can usually start a repair the same week you call. For less common Demilec lines like Agribalance, we order directly and it arrives within 3 to 5 business days.
Call for a Free Estimate
If your Demilec attic insulation is failing, or you suspect it is, call Walt’s Insulation at (866) 751-4428. We’re locally owned and owner-operated since 2000, with a published address and license number – not a franchise, not a call center. A live person answers every call, 24/7. We’ll send a background-checked, uniformed technician to your San Antonio home, give you an honest assessment of what’s failing, and a straight number for what it costs to fix. Free second opinion on any written estimate. No trip charge inside our county. $40 off any repair over $200. Seniors and veterans always save 10%. Talk to a real person, get a straight answer.
Written by Walt Brenner, Owner, Walt’s Insulation at Walt’s Insulation, serving San Antonio and nearby areas.