Demilec Attic Air Sealing Nationwide

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

Demilec attic air sealing in San Francisco typically runs $1,800 to $4,200 installed, depending on attic square footage, access difficulty, and how much existing foam needs remediation first. We stock Demilec-compatible sealants and foam systems on our trucks, and most San Francisco jobs can be scheduled the same week you call. Owners usually discover a problem the way you just did: a spike in the PG&E bill, a draft coming through the attic hatch, or a musty smell that showed up after the first real rain since the foam was installed.

Call (341) 247-0222

You’re here because something in your Demilec system isn’t doing its job anymore. Maybe the foam pulled away from the sheathing. Maybe a section was never fully cured. Or maybe the previous contractor sealed around the chimney chase but skipped the top plates entirely. Whatever brought you here, Neil Barron and our crew can walk the attic with you and tell you exactly what’s holding and what isn’t, before anyone quotes a number.

Which Demilec Models This Applies To

Demilec makes two primary open-cell and closed-cell spray foam lines that San Francisco homeowners run into: Sealection 500 (open-cell, half-pound) and Heatlok HFO (closed-cell, two-pound). Attic air sealing work touches both, but they fail differently. Sealection 500 shrinks slightly over time when attic temperatures swing, which San Francisco’s fog-to-sun cycles accelerate at roof deck level. Heatlok HFO is more rigid and tends to crack at seams where the roof framing moves, especially in older Victorians and Edwardians with true 2×4 rafters.

To identify what’s in your attic, look at the foam color and texture. Sealection is pale yellow to off-white, soft to the touch, and you can press a thumbnail into it. Heatlok is darker cream, hard, and sounds solid when you knock on it. The compatibility gotcha most people miss: you can’t simply spray one over the other without a bond test. Open-cell over closed-cell works if the surface is clean and dry. Closed-cell over open-cell causes condensation traps at the interface, which is a mold risk no San Francisco attic needs. If there’s any doubt about what’s already up there, that’s the first thing we check before recommending a sealing plan.

For air sealing specifically, we also keep Reflectix tape and radiant barrier on hand for duct boots and chase penetrations where foam alone leaves gaps at the metal. Thistledown Insulation San Francisco is an independent installer, not affiliated with Demilec, but we’ve worked with their product lines long enough to know exactly which sealant pairs with which generation of foam.

Signs Your Demilec Attic Air Sealing Is Failing

• Cold drafts near ceiling fixtures on foggy mornings. Air leaks through unsealed top plates and electrical penetrations show up first around recessed lights and ceiling boxes. When foam has pulled back from the framing, you’ll feel it most in rooms directly under the attic access.
• Dust accumulating faster than it should on horizontal surfaces. Attic air pushing down through gaps carries insulation fibers and decades of accumulated dust with it. If your bookshelves look grey three days after dusting, an air seal has opened.
• Uneven room temperatures between floors. A sealed attic keeps conditioned air where it belongs. When one upstairs bedroom runs five degrees warmer than the hallway, conditioned air is escaping through the attic plane, and outside air is replacing it.
• A sudden jump in the PG&E bill without a matching change in behavior. An opened seam in foam sealing can raise heating or cooling load noticeably in a San Francisco flat. Compare against the same month last year, not the month before.
• Condensation stains or mildew smell near the attic hatch. When warm interior air meets a cold attic surface through an unsealed gap, moisture condenses at that exact point. The hatch perimeter is the most common failure spot we see in San Francisco homes, especially older ones with an original pull-down stair.

Replacement Cost & What’s Included

Attic air sealing replacement in San Francisco breaks down into a few line items, and you should expect to see them broken out on any honest estimate:

• Assessment and air leak testing: $150 to $350. We use a blower door or smoke pencil to find exactly where air is moving before we touch anything.
• Foam remediation (if needed): $400 to $1,200. Cutting out failed sections, addressing moisture, and prepping the surface.
• Air sealing labor and materials: $1,000 to $2,200. Sealing top plates, penetrations, hatch perimeters, and chase openings with Demilec-compatible foam and sealant.
• Clean-up and verification: Included. We lay drop cloths from the front door to the attic, wear shoe covers the whole time, and you get a photo of the finished job before we leave.

What drives the range is attic accessibility, how much old foam needs removal, and whether the roof deck has moisture issues that need addressing first. Every quote from us is a written number before work begins. No ranges after the fact, no surprise line items. The work carries our 365-Day Done Right Promise: if the seal doesn’t hold through a full year of San Francisco weather, we come back and fix it. No debate, no fine print.

DIY or Call Us?

Here’s the honest split. An owner can safely check the attic hatch seal, look for visible gaps around plumbing vents and wiring penetrations, and take photos of what the foam looks like at the eaves. That’s useful and we encourage it. What we don’t recommend is buying a DIY two-part foam kit and trying to seal a Demilec attic yourself. The chemistry matters. Mixing a different foam against existing Demilec can prevent proper adhesion, trap moisture, and in a worst case, off-gas into the living space while it cures. Spray foam is not a caulk gun project.

There’s also the roof-to-wall geometry of old San Francisco construction. Balloon-frame walls in neighborhoods like the Outer Sunset and the Richmond open directly into the attic. Miss one gap and you’ve done nothing. Neil grew up in the Valley and learned this trade at Los Angeles Trade-Technical College before years of work on California homes, and he still walks every San Francisco attic himself before writing a single number. Tell me which room keeps you up at night, and we’ll start there. Call (341) 247-0222 and we’ll schedule the walk.

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