Demilec Attic Air Sealing: The San Jose Owner’s Guide
We stock and install Demilec-compatible attic air sealing in San Jose, with most jobs running $1,400 – $3,200 depending on attic size, access difficulty, and how much of the existing seal has failed. We can typically get a technician out same-day or next-day, and every job includes a written price before work starts plus our 365-Day Done Right Promise in writing. Most homeowners discover their Demilec air sealing has failed because a room feels drafty in winter, the AC seems to run constantly in August, or they spot dust streaks on insulation near ceiling penetrations.
Which Demilec Models This Applies To
Demilec’s spray foam products fall into two families that matter for attic air sealing: the Heatlok HFO line (closed-cell) and the Sealection series (open-cell). The Heatlok HFO Pro and Heatlok HFO High Lift are the ones we most often see in San Jose attics, applied as a continuous air barrier at the roofline or at the attic floor. Sealection 500 is common in vaulted ceiling applications where open-cell is preferred for its flexibility.
Here’s the compatibility gotcha: Demilec air sealing is not a replaceable part in the traditional sense. It’s a sprayed-in-place foam that bonds to the substrate. When it fails, you’re not swapping out a gasket or a seal, you’re removing the failed section and re-spraying the right Demilec product for that specific location. If someone tells you they’ll just caulk over it, run. The foam needs to match what’s already there, or you get adhesion failure and the same leak comes back within a season.
We’re an independent San Jose insulation contractor, not affiliated with Demilec. We use their products because they’re proven in California’s heat and because we’ve seen what happens when cheaper substitutes go in. We also stock Reflectix radiant barrier for San Jose attics where reflective heat control makes more sense than foam alone.
Signs Your Demilec Attic Air Sealing Is Failing
- Dust or insulation staining around ceiling fixtures. When the air seal at a can light or ceiling fan box fails, attic air pulls through the gap and deposits fine dust in a circular pattern on your insulation. In San Jose’s dry summers, this shows up fast.
- A room that’s 5 – 8 degrees off from the rest of the house. Air sealing failure means conditioned air escapes into the attic. One bedroom suddenly baking in July while the hallway stays fine is a classic telling sign.
- Visible gaps where foam has pulled away from the framing. Demilec foam can shrink slightly over years of thermal cycling, especially on south-facing roof planes in San Jose. If you can see daylight or a crack between the foam and a rafter, the seal is gone.
- Higher PG&E bills without a rate change. When your usage ticks up but your habits haven’t, the attic is usually the first place to look. Air sealing failure makes your insulation work against itself.
- Pest activity in the attic. Rats, mice, and squirrels in San Jose love squeezing through failed air seal gaps. If you’re hearing scratching at night, the seal may have opened a passageway.
Replacement Cost & What’s Included
For San Jose homes, Demilec attic air sealing repair and reapplication typically runs $1,400 – $3,200. Here’s what drives that range:
- Attic size: A 1,200 sq ft rancher in Willow Glen costs less to reseal than a 3,000 sq ft two-story in Almaden Valley.
- Access: Attics with limited headroom, tight truss spacing, or blown-in insulation covering the work area take longer and cost more.
- Failure extent: One failed section around a bathroom fan is a small job. Complete delamination across the roofline is a full reapplication.
- Prep work: Removing old failed foam, cleaning the substrate, and protecting your existing insulation all add labor hours.
Your quote includes everything: removal of failed material, surface prep, Demilec foam application, and cleanup. No add-on line items at the door. The work is covered by our 365-Day Done Right Promise, and if the repair fails within that year, we return and fix it at no charge. That’s in writing on every job.
DIY or Call Us?
Here’s the honest answer: you can inspect your own attic air sealing safely, but you should not attempt to re-spray Demilec foam yourself. Two-part spray foam requires precise temperature control, proper mixing ratios, and chemical safety equipment including respirators and protective suits. The isocyanate component is an irritant and a sensitizer, meaning repeated exposure can cause respiratory issues. The two-part kits sold at big-box stores simply don’t match what a professional Demilec application provides, and misapplied foam is worse than no foam because it gives you a false sense of security while air still leaks around it.
What you can safely do: photograph any visible gaps or delamination, note which rooms feel drafty or hot, and check your attic access for signs of pest pressure. Then call (669) 333-7274 and send us the photos. We’ll give you a straight answer on what needs to happen and what it costs, before anyone sets foot in your attic.
FAQs
Demilec closed-cell foam (Heatlok HFO) typically holds its air seal for 20 – 30 years in San Jose’s climate, while open-cell Sealection generally lasts 15 – 20 years before it may need section repairs. The biggest threats to lifespan here are sustained attic temperatures above 140°F in summer and repeated thermal cycling, which can slowly break the foam’s adhesion to wood framing over decades. Call (669) 333-7274 and we’ll assess whether your existing foam is still performing before recommending any work.
Yes, localized repairs are possible and are what we do most of the time in San Jose. If the failure is confined to a few penetration points or a delaminated section, we remove the failed foam, prep the area, and re-spray with a compatible Demilec product. Full replacement only makes sense when delamination is widespread, usually on roofs where original installation temperatures were off or the wrong foam was used for the application.
Most San Jose attic air sealing repairs take 4 – 8 hours, including removal of failed foam, surface prep, spraying, and cleanup. Larger reapplication jobs can run a full day or more. We’ll give you a precise time window in writing before scheduling, and you can track our technician’s arrival live through the Relay Visibility Guarantee.
Yes. We carry Heatlok HFO Pro, Heatlok HFO High Lift, and Sealection 500 on our trucks serving San Jose, so most repairs can be completed in a single visit without waiting on a materials order. If your attic has an unusual application or requires a specific Demilec formulation we don’t have on hand, we’ll tell you upfront and schedule accordingly.
Written by Chase Whitaker, Owner, Laurel Attic Insulation San Jose at Laurel Attic Insulation San Jose, serving San Jose and nearby areas.