Demilec Attic Air Sealing Nationwide

Demilec Attic Air Sealing: The San Antonio Owner’s Guide

We stock and install Demilec-compatible attic air sealing in San Antonio, with most jobs running between $900 and $2,800 depending on attic size and how much existing sealing has failed. We can usually have a technician on-site within 24 to 48 hours, and same-week installation is common. Most San Antonio homeowners discover their air sealing has failed when they notice a specific room running noticeably warmer than the rest of the house, or when dust starts collecting on surfaces even with windows closed. The air barrier that should be keeping attic heat out has developed gaps, and in a city where attic temperatures push past 140 degrees in July, those gaps act like a slow leak in a tire.

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Which Demilec Models This Applies To

Demilec makes closed-cell and open-cell spray foam systems used for attic air sealing, and the compatibility picture depends on which line your home has. The Heatlok HFO line is Demilec’s closed-cell workhorse for San Antonio attics, sprayed at one to three inches against the roofline or attic floor. The Sealection 500 is their open-cell option, used where sound dampening and cost matter more than maximum R-value per inch. If you have an older Demilec install from before the HFO transition, you may have Heatlok Soy 200 or Sealection Agribalance, which used a water-blown formula that behaves slightly differently during re-entry and repair work.

Here is the compatibility detail most homeowners don’t know: you cannot reliably patch Demilec closed-cell foam with a different brand’s closed-cell foam and expect the air barrier to behave as one continuous membrane. The cell structure and expansion rate differ enough that micro-gaps form at the seam. We stock Demilec Heatlok HFO and Sealection 500 on our trucks precisely because mixing brands on a repair compromises the seal. For owners who need to verify what they have, look for the Demilec label on a visible section of cured foam, or check the original scope of work from your builder. In San Antonio, we see the most Demilec installs in homes built after 2010 in communities like Stone Oak, Alamo Ranch, and the neighborhoods along Bandera Road.

Signs Your Demilec Attic Air Sealing Is Failing

• A single room that won’t hold temperature. Attic air sealing failures almost always show up as one room running five to eight degrees warmer than the rest of the house. The gap in the air barrier sits directly above that room, letting attic heat press down through the ceiling drywall.
• Dust accumulation with no obvious source. When the attic air seal fails, the attic’s dust load gets pulled into the living space through ceiling penetrations, can lights, and drywall seams. You’ll see fine gray dust on ceiling fan blades within a week of cleaning.
• An attic that smells like the house. This sounds backwards, but it’s a real tell. When the air barrier is intact, attic air and living space air barely mix. When it fails, cooking smells and pet odors drift upward into the attic and then get pulled back down as the house breathes.
• Higher summer cooling bills for no apparent reason. A San Antonio attic sealed with Demilec should hold a consistent temperature profile. When the seal fails, your AC works against a constant stream of 140-degree attic air. You’ll see it in July and August usage against the same months the prior year.
• Visible gaps, cracks, or shrinking around existing foam. Demilec closed-cell foam should look dense and uniform. If you notice pulling away from rafters, cracking along seams, or areas where the foam has been disturbed by rodents or past contractors, the air barrier is compromised.

Replacement Cost & What’s Included

In San Antonio, Demilec attic air sealing replacement and repair typically lands between $900 and $2,800. The lower end covers localized repair on a smaller attic, usually 300 to 600 square feet of failed sealing patched with the matching Demilec product. The higher end covers full removal of compromised material and re-application across a 1,500-plus square foot attic. You will have a written price before we touch anything, and that price includes materials, labor, clean-up, and our 365-Day Done Right Promise.

Every job includes shoe covers and drop cloths from the front door to the attic hatch, a photo of the clean-up before we leave, and an itemized written quote before any work starts. Neil Barron walks every job before quoting it. He wants to see the existing Demilec application, measure the attic clearances, and understand which rooms sit directly below the failure points before he puts a number on paper.

DIY or Call Us?

You can safely check for visible gaps in your attic by looking at the existing Demilec foam from the attic hatch, and you can note which rooms run warmest. That’s useful information and we’re glad to hear it when you call. What we do not recommend is attempting to patch Demilec closed-cell or open-cell foam yourself. Spray foam requires proper ventilation and PPE during application, and the chemicals involved in re-entry are something a homeowner should not handle. Closed-cell foam also expands aggressively, and an over-application in a tight attic space can create pressure issues against the roofline. If your attic air sealing has failed, the job is a re-application, not a caulk bead. Call us at (903) 437-9164 and we’ll get a technician to San Antonio within a day or two to assess it. Estimates are free, and the number we quote is the number you’ll pay.

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