Demilec Attic Insulation Nationwide

Demilec Attic Insulation: The San Francisco Owner’s Guide

Thistledown Insulation San Francisco installs and services Demilec attic insulation throughout San Francisco, with typical installed costs running $1,800 to $4,200 depending on attic size and product line. We stock Demilec-compatible materials on our trucks and can usually schedule an assessment within 48 hours. Most San Francisco homeowners call us because they’ve noticed something specific: a room that won’t hold temperature, a musty smell near the attic hatch, or an energy bill that climbed without explanation.

Call (341) 247-0222

Demilec makes two product families that show up most often in San Francisco attics: open-cell spray foam (Sealection 500) and closed-cell spray foam (Heatlok HFO Pro). We also see older Demilec installations from the mid-2000s using formulations that are no longer manufactured. When that older foam breaks down, we replace it with current Demilec product or a compatible alternative from our eight stocked brands: Owens Corning, Johns Manville, Knauf, Rockwool, CertainTeed, Icynene, Demilec, and GreenFiber.

Which Demilec Products This Applies To

We work with the Demilec lines most common in San Francisco homes. The Sealection 500 is an open-cell, water-blown spray foam that goes in at roughly half a pound per cubic foot. Heatlok HFO Pro is a closed-cell foam with a hydrofluoroolefin blowing agent, giving it a higher R-value per inch and a tighter air seal. Both are legitimate products with different jobs. The compatibility gotcha we see most often: a previous contractor installed Sealection 500 in a San Francisco attic where moisture from the marine layer gets trapped in the open cells. Open-cell foam breathes, and in fog-heavy neighborhoods like the Sunset or Richmond, that can mean damp insulation against the roof deck.

If you have a Demilec label still visible on a beam or attic hatch frame, the model name and date code will be there. Date codes matter. Demilec changed formulations several times between 2005 and 2018. If your foam was installed before 2010, we typically recommend full removal and replacement with a product matched to your attic’s airflow pattern, not the product that happened to be on the truck two decades ago. For OEM versus aftermarket, we’re direct: Demilec’s current open-cell and closed-cell lines are strong products, but we also stock CertainTeed and Icynene equivalents when a different product fits a specific San Francisco attic better. The right product depends on whether your attic is vented or sealed, and whether you store anything up there.

One note on our independence for full transparency: Thistledown Insulation San Francisco is an independent insulation contractor. We are not affiliated with Demilec or any manufacturer. We install what fits the house, not what a brand partnership tells us to push. We also keep Reflectix radiant barrier on hand for the specific San Francisco roof condition where afternoon sun hits an uninsulated rafter bay harder than the rest of the attic.

Signs Your Demilec Attic Insulation Is Failing

We’ve walked into hundreds of San Francisco attics. Here’s what a failing Demilec installation actually looks and feels like from inside the house:

• Temperature swings between floors. The upstairs runs six to eight degrees warmer than the downstairs on a sunny day. This means the foam has pulled away from the roofline or was never thick enough. Pull-away is the number one failure mode we see in older open-cell Demilec jobs.
• A smell you can’t place near the ceiling. Not sewage, not gas. A musty, almost sour smell. This is usually open-cell foam that absorbed moisture over multiple fog seasons. San Francisco’s marine layer pushes humidity into attics that were never designed to handle it.
• Higher PG&E bills without a rate change. When a customer in Noe Valley tells us their winter bill went up 30 percent year over year with the same thermostat settings, we almost always find foam that has shrunk or cracked along the top plate where wall meets roof.
• Visible gaps or crumbling at the foam edges. Spray foam should look like a solid, continuous layer. If you can press a finger into it and it crumbles, or if you see daylight through a seam, the material has degraded past the point of patching.
• Drafty rooms directly under the attic hatch. The hatch is the most common air leak in a Demilec installation. If the hatch wasn’t insulated and weatherstripped when the foam went in, the attic is leaking conditioned air through a two-foot-square hole. This is also the easiest thing for a homeowner to check.

Demilec Replacement Cost in San Francisco

Here’s what a Demilec attic insulation project actually costs in San Francisco. These are installed ranges, including removal of failing material where needed, product, labor, and the full clean-up. Every customer gets a written price before any work begins. Not an estimate range. A number.

What drives the range is attic accessibility, the condition of the existing material, and whether we need to bring in a removal crew for old, failed foam. San Francisco Victorian attics in the Haight-Ashbury and the Mission often have low clearances and older framing that slows the work. That’s reflected in the price. What’s never reflected is a surprise line item at the end. The number we write down before we start is the number you pay. That’s the 365-Day Done Right Promise in practice: if the insulation is not done right within a year of installation, we make it right at no charge.

DIY or Call Us?

There’s one honest safety statement we make on every Demilec assessment: removing spray foam from an attic is not a weekend project. It requires full-body protection and a respirator, and cutting foam off roof sheathing in a tight San Francisco attic often means working around electrical wiring and recessed light cans. The New York Times called out exactly this risk in 2025 when it reported on improper foam removal causing attic fires across New England. We’d rather tell you plainly than see you hurt.

What you can safely check yourself: the attic hatch. Is it insulated? Is the weatherstripping intact? Can you feel a draft at the edges? That takes five minutes and no tools. Everything after that is a job for a crew that does it weekly. Neil Barron, who runs our San Francisco operations, walks every attic himself before writing a single number. He wants to see the framing, the wiring path, and the existing foam condition with his own eyes. That’s how we avoid the difference between a quote and a final bill that surprises people. Call (341) 247-0222 and we’ll schedule the walk.

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