Demilec Attic Air Sealing: The Mountain View Owner’s Guide
We stock and install Demilec-compatible attic air sealing components for Mountain View 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 the scope is straightforward. Homeowners usually figure out something’s wrong when their upstairs rooms won’t hold temperature despite new insulation, or when their PG&E bill climbs in a house that was supposedly sealed already.
Which Demilec Models This Applies To
Demilec’s attic air sealing line centers on their spray-applied polyurethane foam systems, primarily the Heatlok HFO Pro and Heatlok XT series, plus the legacy Heatlok Soy 200 Plus found in many Mountain View builds from 2012 to 2019. The key identifier is the application thickness label on your attic access hatch or rim joist, which should read between 1.5 and 3 inches for thermal barrier compliance under California Title 24. We also see Demilec’s open-cell Sealection 500 in older Los Altos and Mountain View ranch conversions where the original contractor spec’d lighter density for truss load concerns.
The OEM-versus-aftermarket question matters less with Demilec than with mechanical systems because foam is field-mixed and applied, not a discrete part you swap. What we do stock are Demilec-formulated resin and iso components, plus compatible one-component canned foam for detail work around top plates and electrical penetrations. If your original installer used a different brand, we match the existing foam chemistry, not the label. In Rex Manor last month, we found a Heatlok XT job that had been patched with generic big-box foam; the incompatible expansion rates created a gap at the top plate that showed 180 CFM50 on the blower door. We cut it back and re-applied with matched material.
Signs Your Demilec Attic Air Sealing Is Failing
- Uneven room temperatures upstairs. When Demilec foam shrinks or pulls away from framing members, conditioned air escapes through the gap while attic air pulls in. The room beneath the failure point runs cold in winter and hot in summer, and the thermostat in the hallway reads fine while the bedroom doesn’t.
- Dust streaks around ceiling registers or can lights. These dark lines are filtration marks, attic air being drawn through the smallest gaps because the pressure boundary has failed. The Demilec seal at the penetration was either missed originally or has degraded from thermal cycling.
- Ice damming or concentrated roof melt patterns. In Mountain View’s occasional freeze events, warm attic air reaching the sheathing melts snow unevenly. The water runs down and refreezes at the eave. This means your thermal and air boundaries have separated, often because foam was applied over a dirty substrate and never bonded.
- Musty odor after rain. Demilec foam is hydrophobic when intact, but a gap at a chimney chase or vent stack lets moist attic air migrate into wall cavities. You smell it when the pressure stack effect reverses in evening cooldown.
- Blower-door reading above 3,000 CFM50 on a home under 2,500 square feet. We test a lot of Mountain View Eichlers and ranch homes that should read closer to 2,000 CFM50 after proper sealing. If your number’s high and the insulation looks adequate, the air seal is the culprit.
Replacement Cost & What’s Included
Most Demilec attic air sealing jobs in Mountain View run $1,800 to $3,400 for homes between 1,200 and 2,800 square feet. The low end covers targeted remediation, one or two failed areas with accessible top plates and standard penetrations. The high end involves full attic floor sealing, multiple can-light enclosures, chimney chase blocking, and a dam around the access hatch.
What drives the range is labor time in tight attics, not the foam itself. A 1950s Rex Manor crawl-attic with collar ties every 32 inches takes longer than a 1980s tract home with a scuttle and open joist bays. Our price includes the blower-door test before and after, the written scope delivered before work starts, and the Documented Photo Record showing every sealed penetration. Under our 365-Day Done Right Promise, if the post-job blower-door number doesn’t hold, we return and find what moved.
We do not charge separately for the diagnostic test when you proceed with the repair. Written price, flat scope, no surprises. Haven Standard Clause 1.
DIY or Call Us?
There’s a safe middle ground and a hard stop. Homeowners can verify the failure themselves: look for shrunken or cracked foam at the attic hatch, check for daylight through rim joists, or run a smoke pencil around can lights with the HVAC off and a bathroom fan running. Document what you find with photos. That’s useful information, and it costs nothing.
Where DIY ends is the application. Two-component polyurethane foam requires respirators with organic vapor cartridges, full coverage suits, and controlled temperature staging of resin and iso. The exothermic reaction hits 200-plus degrees; misapplied, it can off-gas in the living space or char and fail. California Title 24 also requires a thermal barrier coating in habitable attics, which most homeowners don’t have on hand. We carry the full kit, the ventilation setup, and the fire-rated intumescent where code demands it. For a straight answer on what you’re dealing with, text us a photo of the affected area to (669) 259-0406 and we’ll tell you if it’s a spot repair or a full re-seal.
FAQs
In Mountain View’s climate, properly applied Demilec foam lasts 25 to 30 years before measurable degradation. The failure mode we see sooner is mechanical separation from the substrate, not chemical breakdown, usually from dust, moisture, or temperature swings in unconditioned attics. Annual visual inspection from the hatch catches this early. Call (669) 259-0406 if you see cracking or shrinkage; estimates are free.
Localized repair is viable when the failure is isolated to one or two penetrations and the surrounding foam is firmly bonded. We cut back to sound material, apply compatible foam, and re-test. If the original job was thin or spotty throughout, partial repair leaves you with a patchwork pressure boundary and a blower-door number that won’t improve much. We quote both options so you can see the projected CFM50 difference.
A targeted repair runs three to four hours including setup, cure time, and blower-door verification. Full attic floor sealing on a 2,000-square-foot home takes a full day, sometimes two if we’re also installing baffles at every bay for future insulation. We leave the written scope, the before-and-after readings, and the photo record before we pack up. Call (669) 259-0406 to schedule; same-day starts are available for smaller jobs.
We carry Demilec-compatible two-component foam sets, one-component detail cans, and thermal barrier coatings on every Mountain View service vehicle. For Heatlok HFO Pro and XT series, we match the original density and R-value per inch. We are an independent service provider, not affiliated with Demilec, but we source through authorized distribution and batch-test for expansion and adhesion before field use. If your system is a discontinued series, we cross-match chemistry and document the substitution on your written scope.
Topside Attic Insulation Mountain View is independently owned and operated under The Haven Standard since 2016. We also stock parts for Reflectix radiant barrier systems and other envelope components.
Seal the leaks first. The insulation has nowhere to go if the air does. In Mountain View’s Rex Manor neighborhood and across the Peninsula, we’ve pulled out too many insulation jobs that were done in the wrong order. Wes Okafor keeps a notepad in the truck with what he found in each attic, because the next person who goes up there deserves an honest picture.
Ready to get your Demilec attic air sealing fixed right? Call (669) 259-0406 for a free estimate. We’ll give you a written price before any work starts, a blower-door number you can verify, and a documented record when we’re done. Live person answers, 24/7.
Written by Wes Okafor, Owner & Lead Insulation Technician, Topside Attic Insulation Mountain View at Topside Attic Insulation Mountain View, serving Mountain View and nearby areas.