Demilec Vapor Barrier Installation Nationwide

Demilec Vapor Barrier Installation: The San Francisco Owner’s Guide

Demilec vapor barrier installation in San Francisco typically runs $950 – $2,400 installed, depending on square footage, access to the crawl space or attic, and whether old barrier material needs removal first. We keep Demilec-compatible vapor barrier material on the truck, so most jobs are done in a single visit. The way most San Francisco homeowners discover a failed vapor barrier is not dramatic: a musty smell that won’t quit, a crawl space that smells like wet earth after rain, or floor joists that look darker than they should.

Call (559) 245-9792

What makes vapor barrier work in San Francisco different from, say, Sacramento or Tracy, is the moisture load. Temperate marine air, fog intrusion in the Sunset and Richmond, and older foundations that breathe all push moisture up into floor systems. A vapor barrier that was marginal in a dryer climate fails fast here. We see it regularly in homes built before 1970, especially in the Sunset District and the Excelsior, where a failed Demilec vapor barrier installation is usually a symptom of a bigger moisture-management issue, not the root cause.

We’re an independent San Francisco insulation contractor, not a Demilec dealer or affiliate. We install vapor barrier systems that are compatible with Demilec spray foam and Demilec closed-cell products. If you have a Demilec heatlok or Demilec Polarcore installation and the vapor control layer has failed, what follows tells you what to check and what it costs to make right.

Which Demilec Models This Applies To

Demilec’s product line is primarily spray polyurethane foam, not a branded sheet vapor barrier. The vapor barrier we install alongside or beneath Demilec foam is a material spec, not a Demilec branded part. What matters is compatibility: the barrier must sit correctly against Demilec’s closed-cell foam (like Demilec Heatlok HFO or Demilec Polarcore) or open-cell products without trapping water against wood.

To identify what’s in your home, look for a Demilec label on the foam itself, usually stenciled on the side of the foam in the crawl space or attic. The label will say Heatlok, Polarcore, or Sealection. The vapor barrier material itself is typically 6-mil or 10-mil polyethylene, and the spec depends on whether it’s going under a slab, in a crawl space, or against a foam layer. For San Francisco crawl spaces, we use 10-mil reinforced poly, which holds up to foot traffic during service calls far better than the 6-mil you’ll find at big-box stores. The 6-mil material tears too easily, especially in older San Francisco homes where crews work in tight access points.

The OEM-versus-aftermarket question is simpler than most people expect: Demilec does not sell a proprietary vapor barrier sheet. The barrier you’d get from a Demilec application is contractor-sourced poly. What matters is install quality. Cheap barrier fails at the seams and the edges. A proper San Francisco install means overlapping seams by at least 12 inches, taping them, and running the barrier up the foundation wall past grade line. Skip any of that, and you’ll be back in the crawl space in two years.

Signs Your Demilec Vapor Barrier Installation Is Failing

• Persistent musty odor in the first floor of the home. Vapor barrier that has torn or pulled away from the foundation lets moisture migrate upward, and the smell follows. If you only smell it after rain, that’s a classic sign of an edge seal failure.
• Visible moisture or standing water in the crawl space. A properly installed barrier sheds water; a failed one traps it beneath or lets it pool on top. In the Sunset or Richmond, where the water table and fog keep things damp, this shows up fast.
• Darkened or soft floor joists near the foundation. Moisture wicking up into structural wood is what a vapor barrier is there to prevent. Dark staining near the sill plate means moisture has been sitting too long.
• Torn, loose, or missing sections of poly you can see from the crawl space access point. This is the simplest one. If the barrier looks like it’s been shredded, it has. Rodent activity, plumbing work, and past contractors pulling through tight areas all cause this.
• Condensation on ductwork or plumbing in the crawl space. Warm house air meeting cold metal in a damp crawl space produces visible sweating. If your barrier has failed, the whole space runs humid, and metal surfaces show it first.

Replacement Cost & What’s Included

For a typical San Francisco crawl space, a Demilec-compatible vapor barrier installation runs $950 – $2,400. Smaller homes with clean, accessible crawl spaces sit at the low end; larger homes, homes with low-profile access, or jobs that require removing old failed barrier material first sit at the high end. Homes in the Sunset with post-and-beam construction and low clearances tend to run toward the upper range because labor is slower.

Here’s what that price includes:

• Written price before work starts. The number you approve is the number on the invoice. No add-ons at the door.
• Removal of failed barrier material, when present, bagged and hauled out.
• 10-mil reinforced polyethylene barrier, installed with 12-inch overlapped and taped seams.
• Barrier run up the foundation wall past grade line, sealed at the top edge.
• Written guarantee for 365 days. If the work fails in that window, we return at no charge. That’s the 365-Day Done Right Promise, and it’s in writing on every job.

The cost difference between a $950 job and a $2,400 job is almost entirely square footage and crawl space accessibility. If your crawl space has 18 inches of clearance, expect faster labor and a lower bill. If it’s a belly-crawl at 10 inches, prepare for the higher end.

DIY or Call Us?

There’s a version of this job a homeowner can do, and there’s a version that goes sideways. The sideways version involves tight San Francisco crawl spaces, low clearance, and old damaged barrier that needs removal before new material goes down. Crawl space work on your stomach, in the dark, with rodents having been there, is where a $300 material savings turns into a weekend you’ll regret. Also, if the failed barrier is against your Demilec foam, you can damage the foam pulling the old material loose, and then the repair gets more expensive.

What you can safely do: check the crawl space access point for visible damage, take photos of the Demilec label if you can see it, and note whether the floor above smells musty after rain. Those three data points are enough for us to give you an honest estimate over the phone. For the removal and install itself, call us at (559) 245-9792. The crew is background-checked, uniformed, and carries the material on the truck so the job gets done in one visit.

Good insulation doesn’t announce itself. You just stop noticing the cold.

FAQs