Demilec Vapor Barrier Installation Nationwide

Demilec Vapor Barrier Installation: The Leander Owner’s Guide

Demilec vapor barrier installation in Leander typically runs between $1,800 and $3,400 for a full crawl space or attic application, depending on square footage and whether the space needs prep work for proper adhesion. We stock Demilec-compatible 10-mil and 15-mil reinforced polyethylene barriers on our trucks, and most Leander jobs can be scheduled same-day or next-day. Most homeowners figure out something’s wrong when they notice a musty smell returning after a previous encapsulation, or when they spot condensation beading on ductwork in a Crystal Falls crawl space that was supposedly sealed two summers back.

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Which Demilec Models This Applies To

Demilec doesn’t sell vapor barrier as a standalone branded SKU the way they market their spray foam systems, but their building envelope specifications call for reinforced polyethylene sheeting at 10-mil minimum for crawl spaces and 15-mil for high-traffic or rodent-prone areas. If your home was encapsulated by a Demilec-certified installer between 2015 and 2023, you likely have either a woven-reinforced 10-mil barrier with a 0.13 perms rating or the heavier 15-mil cross-laminated version used in Leander’s clay-heavy soils where ground moisture runs high.

Check the edge tape or seam overlap for a Demilec batch code, usually stamped every 10 linear feet. The critical compatibility gotcha: Demilec’s spray foam adhesive systems are formulated for polyethylene with a specific surface energy. Standard big-box 6-mil sheeting won’t bond correctly, and you’ll see tape failure at seams within 18 months. We carry both the OEM-spec Demilec-compatible barrier and a Knauf-cross-certified equivalent that meets the same permeability and adhesion specs, usually at 15% less cost. The Knauf equivalent carries the same 10-year material warranty. We don’t use the thin stuff. Ever.

Signs Your Demilec Vapor Barrier Installation Is Failing

• Condensation on ductwork or pipes. When the barrier tears at seams or pulls away from the foundation wall, ground moisture re-enters the crawl space and condenses on cooler HVAC lines. In Leander, we see this most where summer ground temperatures stay in the low 70s while attic ductwork drops into the 50s.
• Musty odor returning after months of being gone. A properly sealed vapor barrier should drop relative humidity below 60% year-round. If your dehumidifier is running constantly or the smell is back, the barrier’s compromised somewhere you can’t see, usually at the perimeter where tape failed against dirty concrete.
• Sagging or pooling water on the barrier surface. This means water is getting in from above, a plumbing leak, or the barrier was installed without proper slope to a sump or drain. Standing water destroys polyethylene from the top down, and in Leander’s alkaline soil, it accelerates tape adhesive breakdown.
• Visible tears, rodent damage, or displaced sections. Armadillos and field mice are persistent in Leander’s developing areas. A 10-mil barrier won’t stop determined rodents; the 15-mil woven product will, and we can add mechanical fasteners at stress points where the original installer relied on tape alone.
• Increased energy bills with no HVAC explanation. When humid crawl space air infiltrates through floor penetrations, your AC works harder to dehumidify. We’ve measured 8-12% cooling load increases in Leander homes with failed vapor barriers, especially in the older sections of Crystal Falls where original encapsulation used 6-mil non-reinforced sheeting.

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After

Replacement Cost & What’s Included

Most full vapor barrier replacements in Leander run $1,800 to $3,400. The range breaks down like this:

What drives the top of the range: extensive rodent damage requiring subfloor inspection, failed original adhesive that needs mechanical remediation, or homes where the previous contractor encapsulated over wet soil without a drying period. Every job includes removal and disposal of the old barrier, surface prep with a documented moisture reading, new barrier installation with mechanical fasteners at all perimeter points, and seam sealing with Demilec-compatible tape. Our 365-Day Done Right Promise covers the installation workmanship. Material warranty runs 10 years on the 15-mil product.

DIY or Call Us?

Here’s what you can safely check yourself: walk the crawl space with a flashlight and look for obvious tears, tape lifting at seams, or water pooling. Note any musty smells. That’s it.

Where DIY goes wrong: vapor barrier installation looks simple until you’re working in a 24-inch crawl space on Leander’s gumbo clay, trying to get polyethylene to lie flat and seal against a foundation wall that hasn’t been clean since 2012. The adhesive fails without proper surface prep. Seams leak without roller pressure most homeowners don’t own. And if you’re dealing with a conditioned crawl space with supply ducts, disturbing the envelope without understanding the pressure balance can pull humid attic air into wall cavities. We’ve fixed three Leander DIY jobs this year where the homeowner made the moisture problem worse, not better.

Seal the envelope first. Then fill it. Call (737) 252-7159 and we’ll give you a written price before anyone starts.

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