Demilec Attic Air Sealing: The San Antonio Owner’s Guide
Demilec attic air sealing in San Antonio typically runs $900 – $2,600 installed, depending on attic size, access difficulty, and how much of the existing seal has failed. We stock Demilec-compatible seal kits and matching foam on our trucks, so most San Antonio jobs are done same-day or next-day. A failed Demilec seal usually shows up three ways: your AC runs more than it used to, you feel a draft near the attic hatch, or you spot dust streaks along ceiling corners where air is pulling through gaps.
Demilec spray foam is a closed-cell product, which is good news for San Antonio’s humidity: it acts as its own vapor barrier. But when the seal around penetrations – plumbing vents, electrical chases, recessed lights, the attic hatch itself – cracks or pulls away, conditioned air leaks straight into a 140-degree attic. Your AC fights that all afternoon. We see it all the time in older neighborhoods like Jefferson, Terrell Heights, and Alta Vista, where homes from the sixties and seventies still have original can lights and unsealed top plates. The foam was never the problem. It’s the gaps around it.
Which Demilec Models This Applies To
We work with the Demilec Heatlok HFO line, which covers most residential attics sealed in the past ten years in San Antonio. That includes the Heatlok HFO Pro, Heatlok HFO High Lift, and the older Heatlok Soy 200 and Sealection 500 systems. The compatibility gotcha most homeowners miss: Heatlok High Lift requires a different proportioner setting and a dedicated foam gun tip than the standard HFO Pro. If someone tries to patch High Lift foam with a standard tip, the mix ratio goes off and the patch never fully cures. We carry both tip types on the truck.
If you’re not sure which Demilec product is in your attic, check the equipment tag near the attic access or the original invoice from the installer. The foam itself is the giveaway: Heatlok HFO cures to a pale yellow with a dense, rigid feel, while Sealection 500 is lighter and softer to the touch. For the seal component itself – the perimeter gaskets, hatch seals, and penetration collars – we use OEM Demilec parts when we can get them same-week from our supplier, and quality aftermarket equivalents when lead times stretch. For a San Antonio homeowner, the aftermarket gaskets perform identically as long as the density spec matches: we require 2.0 lb minimum density for any patch foam, same as Demilec’s own product sheet. Aspen Attic Insulation San Antonio is an independent service provider, not a Demilec dealer or affiliate.
One more thing: if your attic has Reflectix radiant barrier stapled over the foam seal, the barrier has to come up in the work area before we can re-seal underneath. We handle that, but it’s worth knowing the barricade isn’t the seal itself – it reflects heat, the Demilec foam stops air. Two different jobs.
Signs Your Demilec Attic Air Sealing Is Failing
- Dust stains along ceiling corners and around light fixtures. Air moving through gaps leaves a visible dust shadow where it enters the living space. If you see dark lines forming where the ceiling meets the wall, conditioned air is pulling attic dust through a broken seal.
- A bedroom that runs five to eight degrees warmer than the rest of the house. That’s usually a failed seal around a duct chase or the attic hatch directly above that room. The AC is working – the air just isn’t staying where you want it.
- You can feel air moving near the attic hatch or pull-down stairs. Stand under the hatch with a damp hand on a hot afternoon. If you feel a breath of air, the hatch seal is gone. This is the most common single failure we find in San Antonio homes.
- Your energy bill jumped without a change in routine. Demilec foam doesn’t degrade much in Texas heat, but the seal around penetrations shrinks and cracks over three to five years of 100-degree attic cycles. When enough gaps open up, the bill shows it.
- Foam pulling away from the top plate or around pipes. Get a flashlight up there. If you see daylight-colored gaps where foam meets wood, that seal is done. The crack may look small, but a quarter-inch gap running the length of one wall moves real air.
Replacement Cost & What’s Included
Typical Demilec attic air sealing replacement in San Antonio:
- Attic hatch seal replacement only: $120 – $220 (parts included, 30 – 45 minutes)
- Perimeter top plate and penetration re-seal, small attic under 1,200 sq ft: $900 – $1,400
- Full re-seal, larger attic with multiple penetrations and hatch work: $1,800 – $2,600
The range comes down to attic height, how many penetrations need work, and whether existing foam has to be cut back before re-sealing. You get a written price before any work starts – always, no exceptions. That price covers the Demilec-compatible foam, gaskets, labor, and haul-off of any scrap. The entire job is covered by our 365-Day Done Right Promise, in writing, covering both labor and materials. If the seal fails within a year, we come back and make it right at no charge. Garrett Sloane’s crews have been doing these attic retrofits across San Antonio for over a decade, and the pricing reflects what the work actually costs, not what a commission-driven sales call tries to invent.
DIY or Call Us?
Here’s the honest split. You can safely check visible gaps around the attic hatch, inspect the perimeter seal with a flashlight, and note where the foam has pulled back from framing. That’s good information to have before you call. What you shouldn’t do is apply spray foam yourself without the right respirator and ventilation, especially in a closed San Antonio attic in summer. Two-part Demilec foam requires accurate mixing, proper PPE, and a trained hand with the gun. A bad mix doesn’t just fail as a seal – it off-gases and can make the attic dangerous to enter until it cures. We also recommend leaving electrical penetrations alone: sealing around old wiring requires knowing what’s safe to foam and what needs a fire-rated collar. If you’ve spotted the gaps and want them sealed correctly, call (361) 213-9499. If your attic’s cooking, your AC is drowning – let’s fix the cause, not just the bill.
FAQs
Expect five to eight years from the perimeter seal in San Antonio’s heat, less if the attic has poor ventilation. The Demilec foam itself can last twenty years or more; what fails is the seal where foam meets wood, which shrinks under repeated 140-degree attic cycles.
Often yes. If the failure is limited to visible cracks and gaps around the hatch and a few penetrations, a targeted repair costs $120 – $400. If the seal has pulled back across entire top plates, a full re-seal is the more honest fix – patching half the perimeter still leaks at the patch edges.
Most San Antonio attics are done in three to five hours, including setup, cutback, re-seal, and cleanup. Hatch-only work runs under an hour. Larger homes or attics with full Reflectix removal can push into a second day, and we’ll set that expectation in the written price before we start.
Yes. We carry Heatlok HFO Pro and High Lift foam, both gun tip types, hatch gaskets, and penetration collars on the truck. If we need an OEM Demilec part that’s not on hand, our San Antonio supplier gets it to us same-week, and we’ll confirm timing before you commit. Call (361) 213-9499 for a free estimate and we’ll tell you exactly what we stock and what it costs.
Written by Garrett Sloane, Owner, Aspen Attic Insulation San Antonio at Aspen Attic Insulation San Antonio, serving San Antonio and nearby areas.