Demilec Attic Air Sealing: The Houston Owner’s Guide
Demilec attic air sealing in Houston typically runs $1,800 to $3,400 installed, depending on attic size and how much prep work the space needs before the foam goes in. We keep Demilec-compatible sealing material on our trucks and can usually get a crew out within 48 hours. That’s the short answer. Now for how this actually plays out in a Houston attic.
Most homeowners don’t wake up thinking about air sealing. They notice it in July, when the upstairs bedroom is eight degrees warmer than the kitchen. Or in August, when the AC runs nonstop and the electric bill climbs past $400. Or they stick their head up through the attic hatch and feel air moving that shouldn’t be moving. That’s when it becomes clear the thermal boundary between the house and the attic has holes in it, and those holes are exactly what Demilec air sealing is designed to close.
What we do with Demilec products is simple. The foam expands on contact and fills gaps that fiberglass batts and blown-in cellulose simply can’t reach: around recessed lights, plumbing vents, electrical penetrations, kneewalls, and the tricky seams where drywall meets framing. In a Houston attic that hits 140 degrees in August, sealing those gaps matters far more than most people think. It’s not about adding more insulation on top. It’s about stopping the air that moves through the insulation you already have.
Which Demilec Models This Applies To
Demilec makes several open-cell and closed-cell spray foam lines, and the air sealing work we’re describing applies to all of them. The most common products we install and service in Houston are Heatlok HFO Pro (closed-cell, the higher R-value option), Sealection 500 (open-cell, the dense and fluffy option that also handles sound), and Sealection Agribalance (open-cell with a bio-based formulation). If your attic was sealed with any of these, the material itself is almost certainly fine. What fails first is what was missing at the time of the original install.
Here’s the compatibility detail worth knowing. Demilec open-cell and closed-cell foams are not interchangeable in the same application. Closed-cell Heatlok adds structural rigidity and a vapor barrier at about two inches thick. Open-cell Sealection does neither. If your attic was originally sealed with closed-cell and you’re patching with open-cell, the thermal and moisture performance changes. That’s the kind of mismatch that creates condensation problems nobody wants in a Texas attic. When we come out for a Houston Demilec air sealing job, we identify exactly what product is already up there, check the manufacturer spec sheet, and match it. We stock both open-cell and closed-cell Demilec material on the truck, plus aftermarket equivalents when they’re the better call for a partial repair.
How do you know what you have? Look for a label, usually a sticker left near the attic hatch or on an exposed rafter by the original installer. It will name the Demilec product and the install date. If the label is gone, a foam sample tells us a lot by touch: open-cell is soft and sponge-like, closed-cell is rigid and dense. Either way, we can identify and match it before anyone opens a can of anything.
Woolsey Insulation Houston is an independent attic insulation and spray foam contractor. We are not affiliated with Demilec, and we have no dealer agreement with them. We install and service their products because they perform well in Houston’s climate, and because homeowners with a failed or incomplete Demilec sealing job keep calling us to fix it. We also work with other attic products like Reflectix radiant barrier when the situation calls for it.
Signs Your Demilec Attic Air Sealing Is Failing
- Uneven room temperatures between floors. The upstairs runs consistently warmer in summer and colder in winter, no matter how you set the thermostat. This means air is moving through the attic floor where the original seal missed penetrations or the foam has separated from framing over time.
- Mysterious dust or insulation particles in the living space. Air leaking through gaps in the attic floor carries fine particles down with it. If you’re dusting more than you ever did, or you see what looks like attic debris around recessed light trims, the seal has a breach somewhere.
- High humidity upstairs during summer. Houston’s humidity is relentless, and a breached attic seal lets moist outdoor air cycle down into the conditioned space. You’ll feel it as dampness, see it as condensation on window interiors, or smell it as a musty cloying odor in closets.
- Running AC constantly with no real temperature drop. The unit is laboring because it’s fighting air infiltration from the attic, not just solar heat on the roof. This is often the point where homeowners call us and say, “It’s not the AC, it’s the house.” They’re usually right.
- Rodent or insect activity in the attic. Critters don’t chew their way past a good foam seal easily, but once a gap exists, they find it. If you’ve had a pest issue, have the attic seal checked after it’s resolved. What they entered through is still open.
Replacement Cost & What’s Included
For an attic air sealing job in Houston using Demilec products, here’s what we see on typical homes. A 1,200 to 1,800 square foot single-story attic typically runs $1,800 to $2,600. A larger or two-story home with a more complex roofline runs $2,600 to $3,400. If the existing foam is in rough shape or there’s old fiberglass to remove first, add $400 to $900 for prep and disposal. We give you the exact written number before any work starts, and that number does not change at the door.
The range comes down to three things: access, prep, and material volume. An attic with a wide hatch, good headroom, and clean decking is fast. An attic with tight angles, old insulation piled everywhere, and 130-degree heat in August is slower. But those conditions affect our labor time, not a markup we invent after seeing the house. The Kingswell Way is simple: say the price, show up in the window, leave it cleaner than we found it, put the guarantee in writing, and come back if it fails within 365 days at no charge. That’s the guarantee on every Demilec air sealing job we do in Houston.
DIY or Call Us?
There’s no safe way to DIY a spray foam air sealing repair. This is one of the few times we’ll be blunt about it. Two-part spray foam is applied at high temperature and pressure, and the chemical reaction is exothermic. Getting it wrong means a bad seal, a chemical mess, or a burned hand. The equipment alone costs more than most repair jobs. If you have a small visible gap, you can note the location and keep the area clear until we arrive. That’s the extent of the safe homeowner prep.
What an owner can safely check: look for daylight coming through the attic at ridge vents or gable ends, note any rooms that feel drafty, and if you have access, take photos of the existing foam color and texture so we can see what’s up there before we arrive. That helps us match product. Then call us at (903) 447-8369. Glenn Hartley and the crew have worked attics from older ranch houses in Meyerland to newer builds out past Katy, and we’ll tell you straight whether the seal is worth repairing or whether the whole attic needs redoing.
FAQs
A properly installed Demilec air seal lasts 20 to 30 years, but Houston’s heat and humidity can expose problems much sooner if the original install was incomplete, the foam wasn’t thick enough, or gaps around penetrations were missed entirely. The foam itself doesn’t fail in a decade. The workmanship around it sometimes does.
Most Demilec air sealing problems can be repaired without removing the existing foam, as long as the original material is still adhered to framing and the gaps are identifiable. We find and seal the breaches, then spot-check the entire attic floor for anything the first installer missed. If the foam has separated from framing over large areas, full redo is the more honest call, and we’ll show you why. Call (903) 447-8369 for an exact quote, and estimates are free.
Most Houston Demilec air sealing jobs take one day, sometimes a half day for smaller attics. If we’re removing old insulation first or the attic is especially large or difficult to access, plan for two days. We’ll tell you the window before we start, and we keep that window.
Yes. We stock both open-cell and closed-cell Demilec material on the truck, along with the spray rig and prep equipment to do a full attic seal in one visit. Part of the reason we maintain our own inventory is simple: we don’t want to tell a Houston homeowner with a hot upstairs that we’ll be back in two weeks because somebody didn’t order material.
It does, and the effect is measurable. Sealing an attic floor reduces the amount of conditioned air lost into the attic, which means the AC runs less, the indoor humidity drops, and the home holds temperature more evenly between floors. Most Houston homeowners notice the comfort difference within a week. The bill difference shows up within one full cooling season. If we wouldn’t put it in our own attic, we’re not putting it in yours.
Written by Glenn Hartley, Owner, Woolsey Insulation Houston at Woolsey Insulation Houston, serving Houston and nearby areas.