Demilec Attic Air Sealing: The Round Rock Owner’s Guide
We stock and install Demilec-compatible attic air sealing components for Round Rock homes, with most completed jobs running between $1,800 and $3,400 depending on attic square footage and penetration count. Same-day service is available when we have your configuration in stock, which covers most Demilec open-cell and closed-cell systems we’ve encountered in Williamson County. Most Round Rock homeowners discover their Demilec air sealing has failed when utility bills spike 20-40% year-over-year, rooms above the garage stay cold in January despite the heater running, or a recent energy audit flags thermal bypasses the original spray foam missed.
Which Demilec Models This Applies To
Demilec’s product line for residential attic air sealing breaks into two families: the Heatlok HFO series (closed-cell, higher R-value per inch, common in Round Rock builds from 2018-2023) and the Sealection 500 open-cell formulations (older installs, typically 2012-2017). The critical compatibility gotcha: Heatlok HFO 2.0 requires a specific substrate primer that earlier Heatlok generations did not, and applying the wrong sealant layer over existing Demilec foam can cause delamination within 18 months in our Central Texas humidity swings.
Identification starts at the application label, usually found on a basement rim joist or attic access hatch if the original installer followed Demilec’s documentation protocol. Look for a four-digit batch code beginning with HL (Heatlok) or SL (Sealection), plus a density rating in lb/ft³. If the label’s gone, we cut a small inspection core - 1″ diameter, patched after - to read the cell structure and density. Closed-cell Heatlok runs 2.0-2.5 lb/ft³ and feels rigid; open-cell Sealection runs 0.4-0.6 lb/ft³ and compresses under thumb pressure.
For OEM versus aftermarket on Demilec specifically: we use Demilec-manufactured sealant for warranty continuity on jobs under ten years old, but switch to equivalent-density Johns Manville or Icynene formulations for older installs where Demilec has discontinued the specific SKU. The performance difference is negligible in blower-door testing; the price difference is typically $180-$240 in material cost on a full attic redo.
Signs Your Demilec Attic Air Sealing Is Failing
- Uneven room temperatures across the second floor. In Round Rock’s Fern Bluff and Behrens Ranch subdivisions, we regularly see Demilec open-cell installations that settled 15-20% in the first five years, leaving gaps at top plates where conditioned air bleeds into the attic. The master bedroom runs three degrees warmer than the hallway because the attic bypass is directly above the bed.
- Dust streaks around ceiling registers or can light trim. These dark lines are filtration soiling - attic air being pulled through gaps the Demilec foam was supposed to seal, carrying fiberglass particles and pollen with it. The foam itself hasn’t failed everywhere; it’s typically pulled away from a hot penetration or shrunk at a top plate junction.
- Ice damming or persistent frost in the attic during rare hard freezes. Round Rock sees maybe two nights below 20°F each winter, but that’s enough to reveal where warm, moist interior air is reaching cold roof sheathing. Demilec closed-cell should prevent this entirely at 2″ minimum thickness; if you’re seeing frost, the application missed a chase or the foam degraded at a critical junction.
- Musty odor intensifying in summer. Demilec’s open-cell formulations are vapor-permeable by design, which works fine in our climate when paired with proper air sealing. But when the air seal fails, humid attic air migrates through the foam into conditioned space. The smell isn’t the foam off-gassing - it’s mold-friendly humidity where it shouldn’t be.
- Blower-door score degradation on a recent energy audit. A well-sealed Round Rock home of 2,400 square feet should test below 1,500 CFM50. We recently re-tested a 2019 Demilec install in Paloma Lake that had drifted from 1,200 CFM50 to 2,800 CFM50 in four years - the foam was intact, but shrinkage at electrical penetrations and a failed chase seal had undone the original work.
Replacement Cost & What’s Included
Demilec attic air sealing in Round Rock typically runs $1,800-$3,400 for partial remediation (targeted penetration sealing, 800-1,200 square feet of attic floor) and $3,800-$5,600 for full attic air sealing with complete Demilec reapplication. The range driver is penetration density: a 1990s-era Round Rock home with twenty can lights, three bath fans, and a truss chase takes roughly triple the labor of a newer build with surface-mounted LEDs and minimal mechanical penetrations.
Every job includes: core sampling and density verification, substrate prep and primer matching to your Demilec generation, spray application to Demilec’s published thickness spec, and post-install blower-door testing with written results. Under Haven Standard Clause 1, you get the written price before any work starts, the written scope, and the written warranty. The 365-Day Done Right Promise covers adhesion failure, shrinkage beyond manufacturer spec, and any missed penetration we should have caught. We also stock Reflectix radiant barrier components for Round Rock homeowners combining air sealing with attic temperature reduction.
DIY or Call Us?
There’s a safe middle ground and a hard stopping point with Demilec foam. What you can check yourself: the application label location, visual inspection for obvious gaps or yellowing (indicates UV degradation if the foam was exposed), and whether your can lights are IC-rated (insulation contact) - non-IC fixtures create a thermal bridge that foam alone cannot solve.
Where DIY goes wrong: Demilec’s two-component spray requires heated hoses, proper substrate temperature (above 60°F for adhesion in our climate), and respiratory protection beyond standard dust masks. More critically, re-sealing an attic without blower-door guidance means you’re guessing at leak location and quantifying nothing. We’ve cleaned up homeowner spray jobs in Round Rock’s Forest Creek and La Frontera neighborhoods where the foam looked adequate but the post-test score barely moved. The material cost was sunk; the labor to remove and redo was double our original quote.
Seal the leaks first. The insulation has nowhere to go until you do. Call (737) 259-7528 for a written price and blower-door assessment.
FAQs
Properly applied Demilec closed-cell foam should perform 20-25 years in our Central Texas conditions; open-cell Sealection typically sees functional life of 15-20 years before settlement or mechanical damage requires touch-up. The killer in Round Rock isn’t age - it’s the 40-60°F daily temperature swings from March through May that stress the foam-to-substrate bond at top plates and chase walls. We inspect these junctions specifically on every revisit. Call (737) 259-7528 to schedule a density check if your install is past year ten.
Localized repair is viable when the failure is isolated to specific penetrations or a single chase, which describes about 60% of the Demilec callbacks we see in Round Rock. We core-sample the surrounding foam, verify density and adhesion, and tie new material into sound existing substrate. Full replacement becomes necessary when the original application was below minimum thickness, the wrong primer was used (common on Heatlok HFO 2.0 jobs done by non-certified applicators), or UV exposure has degraded exposed surfaces. Our written scope specifies which approach applies before any material is ordered.
Most partial remediation jobs in Round Rock finish in one working day; full attic re-dos with blower-door pre- and post-testing typically require two days, with the second day often limited to four hours for final testing and documentation. We stock Demilec Heatlok and Sealection formulations on our Round Rock service truck, so material delays are rare unless your specific job requires a discontinued SKU we need to source. You’ll receive a text when the technician is en route, under Haven Standard: Arrive on schedule.
We maintain Demilec Heatlok HFO, Sealection 500, and compatible primer/sealant on our Round Rock inventory, plus density-matched aftermarket equivalents from Icynene and Johns Manville for discontinued lines. Same-day completion is standard for partial repairs on configurations we’ve encountered before, which includes most Demilec residential attic systems installed in Williamson County since 2012. For rare commercial formulations or import-spec applications, we can typically source within 48 hours. Call (737) 259-7528 with your batch code for same-day confirmation.
Written by Wes Okafor, Owner, Topside Attic Insulation Round Rock at Topside Attic Insulation Round Rock, serving Round Rock and nearby areas.