Demilec Vapor Barrier Installation Nationwide | Walt’s Insulation

Demilec Vapor Barrier Installation: The West Hollywood Owner’s Guide

Demilec vapor barrier installation in West Hollywood typically runs $1,200 to $3,800 installed, depending on square footage, access, and whether we’re working in a crawl space or basement. Most jobs are completed in a single day, and we stock Demilec-compatible barrier materials on our trucks so there’s no week-long wait for parts. Owners usually discover they need this work when they smell musty air rising through floorboards, see condensation on crawl space vents, or find that their energy bills have crept up despite no change in usage. It’s the kind of problem that builds quietly for years before it announces itself.

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Which Demilec Models This Applies To

Demilec’s closed-cell and open-cell spray foam lines, including Heatlok HFO and Sealection 500, are designed to work as air barriers on their own, but a separate vapor barrier installation is often still needed when those products are used in West Hollywood crawl spaces or under slab. The vapor barrier we install is the 6-mil or 10-mil polyethylene sheeting that goes over dirt floors and up foundation walls before or alongside Demilec foam application. If your home has Demilec foam in the rim joist area but no ground vapor barrier underneath, that’s the gap we’re filling. Demilec’s technical data sheets call for a ground cover in vented crawl spaces regardless of which foam product you use, and that’s a spec a lot of installers skip.

We’re an independent installer, not affiliated with Demilec, but we’ve worked with their products long enough to know the compatibility details that matter. The barrier thickness matters less than the lap and seal method: Demilec’s specs call for a minimum 6-inch overlap at all seams, sealed with contractor-grade tape, and the barrier must run at least 6 inches up the foundation wall. Skip the wall run-up and you get moisture wicking in at the sill plate, which is exactly where West Hollywood’s older pier-and-beam houses show rot first.

Signs Your Demilec Vapor Barrier Installation Is Failing

• Musty odor that gets stronger in summer. When the ground barrier tears or separates at a seam, soil moisture evaporates into the crawl space and gets pulled into living areas as warm air rises. In West Hollywood’s dry summers, the contrast between outside air and crawl space humidity makes this smell more noticeable, not less.
• Cupping or warping hardwood floors. Moisture migrating up through a compromised barrier hits the underside of flooring and causes expansion. We see this in older West Hollywood homes near the Santa Monica Boulevard corridor where original oak floors sit directly over vented crawl spaces.
• Condensation on crawl space vents or ductwork. If you shine a light into the crawl space and see water beading on metal ducts, the barrier isn’t containing ground moisture. This also shortens the life of your insulation and can rust out duct connections.
• Higher energy bills with no obvious cause. Wet insulation loses R-value fast. A damp crawl space means your HVAC works harder to condition the same square footage, and the bill tells the story before you ever look under the house.
• Visible tears, gaps, or missing barrier sections. Rodents, plumbing repairs, and even past termite treatments routinely damage vapor barriers. If you can see dirt through a seam or the barrier has pulled away from the foundation wall, it’s time to address it.

Replacement Cost & What’s Included

For a typical West Hollywood crawl space of 800 to 1,200 square feet, a full Demilec-compatible vapor barrier replacement runs $1,200 to $2,400. Larger spaces, low clearance, or extensive debris removal can push that to $3,800. The work includes removing and disposing of the old barrier, grading the ground surface, installing new 10-mil polyethylene sheeting with sealed overlaps, running it up foundation walls, and sealing around piers and plumbing penetrations. We price it as one number: labor, materials, and cleanup, so you know the total before we start. Every job carries the Done Right Promise, which means if the barrier fails due to our workmanship, we come back and make it right at no charge. No fine print, no runaround.

DIY or Call Us?

Installing a vapor barrier is not inherently dangerous like garage door springs or electrical work, but it is miserable work done in a space most people never want to enter twice. You can safely inspect your current barrier: shine a light under the house and look for tears, gaps at seams, and whether the barrier runs up the foundation wall. What you can’t easily do is haul 100-foot rolls of 10-mil polyethylene through a 24-inch access door, cut it around piers without leaving gaps, and seal seams with tape that actually holds in humid conditions. We’ve fixed plenty of homeowner attempts where the barrier looked fine from the access point but had gaps at every pier and seam. If you want it done once, call us at (213) 527-4062. Walt Brenner has been crawling under West Hollywood houses since 2000, and he’ll give you an honest read on what you actually need.

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