Demilec Attic Insulation Nationwide

Demilec Attic Insulation: The San Marcos Owner’s Guide

Demilec attic insulation replacement in San Marcos typically runs $2.80-$4.20 per square foot installed for open-cell spray foam, and $3.50-$5.80 for closed-cell, with most single-family attic jobs landing between $3,200 and $6,800 depending on thickness and conditioned square footage. We stock Demilec-compatible material on every truck and can usually start the same day you call. Most San Marcos homeowners discover their Demilec insulation is failing when utility bills spike 20-40% year-over-year, rooms above the garage stay hot in July, or they find crumbling, yellowed foam near roof penetrations where Texas heat has degraded the material past its service life.

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Which Demilec Models This Applies To

Demilec, now operating under Huntsman Building Solutions, produced several product lines common in Central Texas attics. The open-cell Heatlok HFO Pro and the closed-cell Heatlok XT are the two we encounter most often in San Marcos homes built between 2010 and 2020, particularly in the Blanco Vista and Willow Creek subdivisions where spray foam became standard during that construction boom. You can identify your product by the application tag the installer was required to leave, usually stapled to a rafter or the attic access hatch. Look for a Demilec lot number, the applied thickness in inches, and the date of installation.

Here’s where compatibility gets specific: Heatlok XT is a 2.0 lb density closed-cell foam rated at R-7 per inch, and it does not interface cleanly with newer Huntsman formulations if you’re doing a partial repair. The color shift is your tell, old XT oxidizes to a dull amber, while current production stays cream-colored longer. For patching, we match density and expansion rate rather than chasing exact OEM chemistry, which matters more for thermal bridging than brand loyalty. We are an independent service provider, not affiliated with Demilec or Huntsman, and we source equivalent-performing material from our supplier network that meets the same ASTM E84 and ICC-ESR certifications without locking you into a single manufacturer.

Signs Your Demilec Attic Insulation Is Failing

• Hot spots on the ceiling in August. When Demilec open-cell foam shrinks or pulls away from rafters, thermal bypass channels form. We find this most often where roof decking hits 140°F in San Marcos summers, exceeding the long-term stability threshold of older HFO-blown formulations.
• Musty smell from attic access after rain. Closed-cell foam is your vapor barrier; when it cracks at truss heels or around chimney framing, humid Gulf air infiltrates and condenses on cooler surfaces. The foam itself doesn’t mold, but the adjacent OSB or drywall will.
• Ice damming or heavy frost on nails in winter. This seems backwards for Texas, but January cold snaps drive condensation on inadequately insulated nail shanks. It signals that your effective R-value has dropped below the dew point margin for your indoor humidity level.
• Visible crumbling or powdering at the foam surface. UV exposure through gable vents or turbine openings degrades the polymer chains. Even indirect light over years will turn the top layer friable, and that dust circulates through your HVAC if the return path runs through the attic.
• Blower-door numbers that have crept back toward pre-retrofit levels. The R-value tells you how slow heat moves through the material, the blower-door number tells you whether any of that matters. If your home was at 2,800 CFM50 after the original Demilec job and now reads 4,100, the foam has separated at critical joints or rodents have compromised the air barrier.

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After

Replacement Cost & What’s Included

Most full Demilec attic re-dos in San Marcos fall between $3,200 and $6,800 for a 1,800-2,400 square foot home with standard 6:12 roof pitch. Partial remediation, where we remove failed sections and feather in new material, runs $1,400-$2,800 depending on accessibility and whether the original was applied to the roof deck or the attic floor.

What drives the range: roof pitch above 8:12 adds labor for safe platform work, existing foam that contains old HFC blowing agents requires specialized disposal per Hays County guidelines, and homes near the San Marcos River corridor often need supplemental dehumidification planning because the ambient moisture load changes the vapor barrier calculation. Every job gets a Written Price Before Any Work Starts, no exceptions, Haven Standard Clause 1. The 365-Day Done Right Promise covers adhesion failure, shrinkage beyond industry tolerance, and any thermal bridging we should have caught. You also receive a Documented Photo Record and, on applicable jobs, the before-and-after blower-door readings on a single printed page.

DIY or Call Us?

There’s a short list of what a San Marcos homeowner can safely assess themselves. Check the application tag for install date and product line. Shine a flashlight across the foam surface to spot shadow lines where material has pulled away from framing. Note any new stains on the ceiling drywall below. These observations help us, but they don’t fix the problem.

What goes wrong with DIY: spray foam requires controlled temperature, humidity, and substrate conditions that an attic in July or January rarely provides. Off-ratio mixing, common with rental equipment, produces foam that feels right on day one and crumbles by month six. The respiratory hazard is real, isocyanate exposure during application demands supplied-air respirators, not the dust masks sold at hardware stores. And without a blower-door test, you’re guessing whether the air barrier is continuous. We’ve found $800 DIY jobs that became $4,200 removals because the chemistry failed and trapped moisture against the roof deck. If you’re considering this, call us for a Free Second Opinion on any written estimate you’ve already received. We’ll read it with you and tell you what we see.

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