Fast, Reliable Spray Foam Insulation Across San Francisco
Spray foam insulation in San Francisco is not like the rest of California. Almost everywhere else, the conversation starts with blocking summer heat. Here, the fog that rolls through the Outer Sunset, Richmond, and Ingleside for most of the year means we’re usually solving the opposite problem: holding modest indoor heat in while keeping persistent, fog-driven moisture out of framing that has stood since the 1880s. Our crews work in San Francisco weekly, know the difference between a Victorian balloon frame and a Sunset-style stucco box, and can be at your door fast when you call (909) 768-6501. We serve the whole city, from the Presidio down to Visitacion Valley.
Why Thistledown Attic Insulation Is San Francisco’s Preferred Spray Foam Insulation Company
We are a Cedarwell-family company, founded in 2003, and every San Francisco job runs on the same Cedarwell Care Promise: shoe covers at the door, drop cloths down the hallway, quiet tools when the baby naps, and a photo of the clean-up before the van leaves. Neil Barron leads our crews, and the standards he set are simple. Written price before any work starts. Background-checked, uniformed technicians on every visit. A live person answers our phone 24/7, so when a San Francisco homeowner calls at 9 p.m. about a cold wall in the Outer Richmond, they get a human, not a voicemail tree. And if something isn’t right after we leave, the 365-Day Done Right Promise means we come back and make it right, no debate.
We install spray foam across every San Francisco neighborhood, from Noe Valley flats to mid-century homes out by Lake Merced. The product matters less than the person deciding where to put it, and our technicians have opened enough San Francisco walls to know what they’ll find before the first can of foam comes off the truck. You get a plan, a written number, and a clean floor when it’s over.
Garage Spray Foam Insulation in San Francisco
Garage spray foam insulation in San Francisco often targets the shared wall and ceiling between an attached garage and a living space, especially in the city’s older flats where a drafty garage sits directly under a bedroom. A typical garage ceiling spray foam job in San Francisco runs $1,400 – $3,200 depending on square footage and whether we’re sealing the rim joists at the same time. That number is written down before any work begins.
Cold Floors Above the Garage
In a 1920s Richmond District flat, the garage below the living room was never insulated, and the floor upstairs never warms up. We spray closed-cell foam across the garage ceiling, air-sealing it in one pass. The result is immediate: the floor stops drafting, and the garage stops pulling cold, damp air into the house envelope every night.
Rim Joist Sealing
Where the garage framing meets the foundation, gaps let fog-heavy air move freely. We spray the rim joist band with closed-cell foam to seal it. It’s a smaller job, often $700 – $1,300, and it stops the slow, damp air infiltration that makes a garage feel like a cave.
Closed Cell Spray Foam Insulation in San Francisco
Closed cell spray foam insulation in San Francisco is the material we recommend most often for exterior-wall retrofits in the fog belt, because it acts as a vapor barrier and structural reinforcement in one application. A closed-cell exterior wall retrofit on a typical San Francisco row house runs $3,800 – $7,500 for a single exposure, but the exact written price depends on what’s behind the wall and how much of it we need to open. It’s not a heat-blocking play here. It’s a moisture-management play.
Vapor Control in Fog-Belt Walls
The western half of San Francisco sits under marine fog for the majority of the year, even in July, when the average high is roughly 65°F. That means exterior stucco stays damp for long stretches, and any insulation we put in has to manage inward vapor drive without trapping it against the original redwood shiplap sheathing. Closed-cell foam, applied correctly, stops that inward drive.
Air Sealing in Old Framing
Victorian and Edwardian row houses were built with zero wall-cavity insulation, and they leak air through every bay. Closed-cell spray foam fills those irregular cavities while sealing the framing joints. When we pull old horsehair plaster, we inspect the sheathing first, because spraying foam against rot or chronic moisture staining from decades of fog is a recipe for trapping the problem inside the assembly.
Trusted Brands We Service in San Francisco
We install Icynene and Demilec closed-cell products for most San Francisco retrofits because their formulations hold up to the city’s persistent humidity, and we also work with Owens Corning and Johns Manville open-cell lines where the assembly is a good fit. Our Spray Foam Insulation team keeps local stock staged for San Francisco jobs, so we don’t lose a day waiting on a truck from a distributor. For older homes, the right product matters less than the right call on vapor direction, and we match the foam to the wall, not the other way around.
Common Spray Foam Insulation Problems We See in San Francisco Homes
- Open-cell foam against fog-soaked stucco. San Francisco’s western fog keeps exterior stucco damp for months at a time. If open-cell foam is applied directly against that stucco without a vapor-managed assembly, it traps inward vapor drive, condenses against the original redwood shiplap, and quietly rots the framing from the inside out.
- Foam over irregular horsehair plaster. Original plaster in a Victorian flat isn’t uniform. Thickness varies, and moisture content varies with it. Spraying foam directly over it can create uneven adhesion and hidden voids that eventually blister or delaminate behind the wall.
- Borrowed summer-heat logic from hotter Bay Area cities. Prioritizing high R-value over vapor control leaves a San Francisco wall unable to dry. The wall feels warmer for a season, then moisture stains reappear behind the foam because the assembly never had a drying path.
- Unsealed rim joists in attached garages. Fog-heavy air moves through those gaps all year. Insulating the garage ceiling without sealing the rim joists leaves the damp air path intact, and the homeowner wonders why the garage still feels humid in August.
Pricing for Spray Foam Insulation in San Francisco, CA
Here’s what we tell San Francisco homeowners before we schedule anything. Garage ceiling spray foam: $1,400 – $3,200. Rim joist sealing: $700 – $1,300. Closed-cell exterior wall retrofit on one exposure: $3,800 – $7,500. Whole-attic spray foam on a typical flat: $2,800 – $5,600. What moves the number is square footage, accessibility, and how much existing material we need to remove before spraying. You’ll have your exact written price before anyone picks up a tool, and that’s not an estimate, it’s a guarantee. Call (909) 768-6501 for a free estimate and a same-week visit.
We Also Serve Cities Near San Francisco
Beyond San Francisco, our crews serve Daly City, Sausalito, South San Francisco, and Alameda. Each has its own microclimate and housing stock, and we spec the foam differently for a fog-soaked Daly City hillside than for a sunnier Alameda bungalow. The written-price promise and clean-up standard travel with us to every job.
Serving San Francisco, CA - Our Local Coverage Area
We’re based in the San Francisco area and know this community well. Use the map below to see our service coverage - if you’re nearby, we can almost certainly help.
FAQs About Spray Foam Insulation in San Francisco
Open-cell foam is vapor-permeable, which means it lets moisture pass through it. In San Francisco’s fog belt, where the exterior of a stucco wall stays damp for most of the year, that permeability allows inward vapor to reach the original redwood shiplap and condense there. In drier cities like San Jose or inland Daly City pockets, that same open-cell foam can dry outward through the wall assembly. In the Outer Sunset, it often can’t. We typically specify closed-cell foam for fog-belt exterior retrofits because it blocks the inward drive entirely. Call (909) 768-6501 and we’ll assess your specific wall before recommending a product.
Usually no, not directly. Original horsehair plaster in San Francisco’s Victorians and Edwardians has irregular thickness and decades of absorbed moisture from the city’s fog. Spraying foam directly over it risks uneven adhesion and hidden voids. We typically remove small inspection sections first, check the sheathing and moisture content, and then decide whether to spray against the sheathing or use a different approach. We’ll give you that answer in writing before we start.
Almost always the same thing: original redwood shiplap sheathing with zero insulation and chronic moisture staining from decades of fog-driven humidity. The west exposure is usually the worst. If we spray without confirming the assembly’s drying direction and sheathing condition, we can trap moisture inside and rot the old-growth redwood framing that still holds up much of the Sunset. That’s why we inspect before we spray, every time.
Yes, specifically because of the damp. A garage in a San Francisco flat is usually a cold, humid air source that leaks into the living space above it. Spraying the garage ceiling and sealing the rim joists cuts that air path and makes the room above noticeably warmer and drier. It’s one of the highest-return insulation jobs we do in the city, especially in the Richmond and Sunset where garages stay damp year-round.
We use Icynene and Demilec closed-cell for most San Francisco exterior retrofits, and Owens Corning or Johns Manville open-cell where the assembly is a good fit. The brand matters less than the vapor-management decision. In San Francisco’s fog belt, a “top-rated” open-cell product specced for a hot, dry city will still fail if it’s installed against a fog-soaked stucco wall. The call is about vapor drive, not brand loyalty.
Contact Thistledown Attic Insulation in San Francisco
If your San Francisco home has cold walls, damp garage ceilings, or drafty rooms that never warm up, we’ll come look. Neil Barron and our crew will walk the job with you, explain what we’d do and why, and hand you a written price before we touch anything. Call (909) 768-6501 for a free estimate any hour of the day. A live person answers.
Written by Neil Barron, owner of Thistledown Attic Insulation, serving San Francisco since 2003.