Demilec Attic Air Sealing Nationwide

Demilec Attic Air Sealing: The San Francisco Owner’s Guide

We stock and install Demilec-compatible attic air sealing in San Francisco, with most jobs running $850 to $1,900 depending on attic size and how much of the existing seal has pulled away. Our crews carry Demilec sealant and the standard application tools on the truck, so most San Francisco homes are done same-day. You usually find out your air seal has failed because the upstairs feels drafty in August when the fog rolls through the Sunset, or your PG&E bill climbs even though nothing else changed. The seal between your attic floor and the conditioned space below is what stops that stack effect, and when it fails, you feel it within a season.

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Here’s the straight answer on cost, compatibility, and why this part fails in coastal air: most Demilec attic air sealing failures we see in San Francisco aren’t the foam itself. They’re failures at the joints and penetrations, where spray foam meets old framing that’s been moving for eighty years. Sealant rated for a dry Denver attic behaves differently after ten fog seasons in the Richmond District.

Which Demilec Models This Applies To

Demilec makes spray polyurethane foam systems under two main lines: Sealection (open-cell, half-pound foam) and Heatlok (closed-cell, two-pound foam). For attic air sealing specifically, most San Francisco homes built before 1980 were sealed with Sealection 500 or Sealection Agribalance if the work was done in the last fifteen years. Heatlok HFO High Lift and Heatlok Soya are the closed-cell options we see in newer retrofit work, particularly in homes where the attic was also being converted to storage or a bonus room.

Identifying your sealant matters because open-cell and closed-cell Demilec products don’t patch the same way. Open-cell Sealection can be top-dressed with a compatible open-cell product. Closed-cell Heatlok needs mechanical removal of the failed section and a proper two-part application; you can’t half-patch closed-cell and expect it to hold. Here’s the compatibility gotcha we run into constantly in San Francisco: homes sealed before roughly 2010 often used Demilec’s older generation of Sealection with an HFC blowing agent, and no current product bonds reliably to it. If your label is gone and you’re not sure what was applied, we do a small test patch before quoting the full repair, because guessing up front is how you end up paying twice.

For the OEM-versus-aftermarket question: Demilec doesn’t sell a “seal” as a replacement part in the way a furnace has a swappable igniter. The air seal is the installed foam system. “Aftermarket” in this context means a different foam manufacturer’s product claiming compatibility. We don’t do that. We stock Demilec Sealection and Heatlok products plus the standard closed-cell primers Demilec recommends for retrofits, because mixing polyurethane chemistry across brands on an existing seal is how you get a bond that fails in 18 months. We also stock Reflectix radiant barrier material for the attic assembly where it’s called for in San Francisco’s climate.

Signs Your Demilec Attic Air Sealing Is Failing

• Drafts near attic hatches and can lights. The air seal at these penetrations is usually the first to let go, because the foam is thin there and the framing moves. A candle or tissue held near the hatch will move when the furnace is off and the attic is warm.
• Upstairs rooms hotter in summer, colder in fog season. Once the stack effect has a path, unconditioned air moves into your living space steadily. This isn’t a gap you see; it’s a slow, constant exchange you feel as uneven room temperatures.
• Dust accumulating faster than it used to. Failed air sealing stops doing its second job, which is keeping fine attic particulates, old insulation dust, and whatever the previous owner’s critters left behind from sifting down through cracks.
• Utility bills trending up against last year’s usage. In San Francisco you can use the same month year-over-year and see a 15 to 20 percent jump with no other explanation. Failed air sealing is usually the quiet culprit.
• Visible gaps in foam at framing junctions. If you look in the attic and see pull-away, shrinkage cracks, or foam that’s turned brittle and begun to flake, the seal has mechanically failed. In coastal air, this shows up as a chalky, crumbly texture that doesn’t spring back when pressed.

Replacement Cost & What’s Included

In San Francisco, complete Demilec attic air sealing replacement runs $850 to $1,600 for a typical 800 to 1,200 square foot attic where we’re removing the old failed seal and re-applying. If the attic has been converted or has extensive mechanical runs and recessed lighting to work around, the job can go to $1,900 or a bit beyond. You’ll see the biggest spread between quotes based on whether the contractor actually removes failed open-cell foam first, or just sprays a bandage over the top. The Alden price includes full removal of failed material, vacuum cleanup of the work area, re-application of Demilec Sealection 500 or a Heatlok closed-cell product matched to what your home had originally, and a walk-through after the foam sets.

Every quote is written before work starts, and the number on the quote is the number on the invoice. The work carries the 365-Day Done Right Promise: if your air seal fails within the year, we come back and make it right at no charge. That promise is in writing on every San Francisco job we do, and it’s the same guarantee whether the attic is in a 1912 Edwardian in the Haight or a 2005 build in Mission Bay.

DIY or Call Us?

Here’s the honest breakdown. You can safely do the inspection work yourself: check for visible foam pull-away at framing joints, test for drafts at the attic hatch with the furnace off, and note where you feel the temperature change most dramatically. You should not attempt a Demilec re-seal with a can of consumer spray foam from the hardware store. That product is not the same chemistry as Demilec Sealection or Heatlok, it will not bond reliably to the old material, and in the worst case you’ll trap moisture against framing and accelerate rot in a San Francisco climate that already fights you on the humidity front. The professional application is a two-part chemical system sprayed at controlled temperature and pressure. It’s not a caulking job.

If you’ve got visible failure or you’re seeing the energy and comfort symptoms above, call us at (559) 245-9792. We’ll put a background-checked, uniformed technician in your attic, find the actual failure points, and give you a written price to fix it right.

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