Demilec Attic Air Sealing: The San Jose Owner’s Guide
We install and service Demilec-compatible attic air sealing throughout San Jose, with most air sealing jobs running between $1,200 and $3,800 depending on attic size and how much of the existing seal has failed. Same-day and next-day appointments are available for San Jose homeowners, and we keep Demilec-compatible sealant materials stocked on our trucks so there’s no second trip waiting on a shipment. Most owners discover the problem the hard way: a utility bill that climbs month after month, a bedroom that won’t hold temperature, or dust showing up on surfaces that used to stay clean.
Attic air sealing is the layer of spray-applied sealant that closes the gaps between your living space and the attic, around penetrations like recessed lights, plumbing vents, wiring runs, and top plates. When it fails, conditioned air leaks out and attic air gets pulled in. The fix is specific to the product line, and Demilec’s open-cell foam behaves differently from its closed-cell products when it ages. Get the match right and the seal lasts. Get it wrong, and you’ll be back in the attic within a year.
Which Demilec Models This Applies To
Demilec makes several spray foam lines used for attic air sealing, and the compatibility question matters more than most homeowners expect. The main products we work with in San Jose attics are Sealection 500 (open-cell, low-density, the most common for air sealing in existing homes), Heatlok HFO (closed-cell, used where moisture control and higher R-value per inch matter), and the older Sealection Agribalance line still found in homes built 10 to 15 years ago. Each has different expansion rates, different reapplication requirements, and different failure patterns.
Here’s the compatibility gotcha most San Jose owners don’t know: open-cell and closed-cell Demilec products cannot be used interchangeably for a repair. If your attic was sealed with Sealection 500 open-cell and you patch with a closed-cell product, the vapor permeability changes and you risk trapping moisture at the seam. We identify the original product from the label if it’s still visible on the attic lid or rim joist area, or by a small test patch when the label is gone. Demilec does not sell direct to homeowners, so every material we use comes through authorized distribution channels, and we are an independent service provider, not affiliated with Demilec as a manufacturer.
Signs Your Demilec Attic Air Sealing Is Failing
- Drafts near ceiling fixtures in winter. When the seal around recessed lights and electrical boxes degrades, you’ll feel cold air settling around the fixture trim even with the HVAC running. The foam has pulled away from the penetration and is letting attic air through.
- A bedroom or hallway that’s 4 to 6 degrees off from the rest of the house. In San Jose ranch-style homes especially, uneven temperatures usually trace back to failed sealing at the top plate where interior walls meet the attic. One compromised run of sealant affects an entire room zone.
- Dust accumulating faster than it should. Attic air carries fine particulate from insulation and roofing materials. When air sealing fails, that dust gets drawn into the living space through the same gaps that leak air. You’ll notice it on window sills, ceiling fans, and dark furniture.
- A utility bill that rose 15 to 30 percent without a matching change in usage. Air sealing failure forces your HVAC to condition air that never stays in the house. In San Jose’s summer heat and winter cool spells, that loss compounds daily.
- Visible cracking, shrinking, or separation in the foam at the attic access. Open-cell Demilec foam naturally settles and can pull back from surfaces after 10 to 15 years, especially in attics with high temperature swings. We see this consistently in San Jose attics with inadequate venting.
Replacement Cost & What’s Included
Most Demilec attic air sealing replacement jobs in San Jose run between $1,200 and $3,800. The range comes down to three things: attic square footage, how much of the existing seal has failed (spot repair versus full re-seal), and accessibility. A 1,200-square-foot ranch attic with straightforward access trends toward the lower end. A larger two-story home with tight knee-wall cavities and failed seals across multiple penetrations lands higher.
You get a written price before any work starts, every time. That price includes labor, Demilec-compatible sealant material, cleanup, and our 365-Day Done Right Promise in writing. If the seal fails within 365 days, we come back and fix it at no charge. No hourly billing, no material surcharges added at the door.
DIY or Call Us?
What you can safely do: check the attic access panel for obvious gaps, look for visible cracking along the foam line at the attic lid, and document where you feel drafts inside the house. That information helps us quote faster.
What you should not do: attempt to reapply spray foam air sealing yourself. Demilec products are two-part chemical systems that expand rapidly and require proper PPE including respirators and skin protection. Improper mixing or application will not cure correctly, and you’ll end up paying more to fix a bad DIY patch than the original repair would have cost. We also see homeowners accidentally seal over ventilation channels, which creates moisture problems that show up months later as mold on the ceiling drywall. Call us at (669) 333-3579 and we’ll assess it properly.
FAQs
Open-cell Sealection 500 typically lasts 10 to 15 years in San Jose attics before showing meaningful shrinkage or separation, while closed-cell Heatlok can last 20-plus years. Bay Area temperature swings and attic heat accelerate aging compared to coastal climates with more stable temperatures.
Yes, if the failure is localized to specific penetrations like recessed lights or a plumbing vent, we can spot-repair just those areas. If the foam is pulling back across the entire attic lid or showing age-related shrinkage everywhere, a full re-seal is more cost-effective and delivers the energy performance you’re paying for. Call (669) 333-3579 and we’ll tell you which applies to your attic before you spend a dollar.
Most San Jose attic air sealing replacement jobs finish in one day, usually 4 to 7 hours including setup and cleanup. Larger attics or jobs requiring extensive old-foam removal may run into a second morning.
Yes. Our San Jose crews carry Demilec-compatible open-cell and closed-cell sealant stock, along with materials from other brands we service including Owens Corning, Johns Manville, and Reflectix. We show up ready to work, not ready to quote a second visit for materials.
Your Next Step
If your Demilec attic air sealing is failing, call us at (669) 333-3579 for a free estimate. We’ll walk your attic, show you exactly what’s failed and what it’ll cost to fix, and put the number in writing before any work starts. Glenn Hartley runs the crew here in San Jose, and he’ll be the one making sure the seal is right, the attic is clean, and the guarantee is in your hand. Get the R-value right, and the house does the rest of the work for you.
Written by Glenn Hartley, Owner, Woolsey Insulation San Jose at Woolsey Insulation San Jose, serving San Jose and nearby areas.