Demilec Crawl Space Encapsulation Nationwide

Demilec Crawl Space Encapsulation: The Seguin Owner’s Guide

Demilec crawl space encapsulation systems in Seguin typically run between $3,800 and $7,200 installed, depending on crawl square footage and whether the foundation needs full vapor barrier coverage or spot repair. We stock Demilec-compatible polyethylene vapor barriers, seam tape, and closed-cell spray foam for perimeter band joist sealing, and most encapsulation jobs in Seguin are completed in one to two days. Most homeowners realize something’s wrong when their hardwood floors cup during our humid spring months or they catch a musty smell that the HVAC seems to recycle through every room.

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Which Demilec Models This Applies To

Demilec’s crawl space line centers on their Heatlok HFO High Lift and Heatlok XT series, both closed-cell spray foams used to seal rim joists and foundation walls, paired with reinforced polyethylene vapor barriers for the ground plane. The critical compatibility point: Demilec’s HFO formulation requires a specific substrate temperature at application, minimum 60°F, which in Seguin’s variable Hill Country winters means we sometimes tent and heat a crawl space before foam goes up. Other installers skip this step, and the foam delaminates within two seasons.

To identify your system, look for the Demilec lot number sticker on any exposed foam surface, or check your original invoice for the Heatlok series designation. If you have a generic white or clear vapor barrier with no mil rating stamped on it, it is not Demilec-spec; Demilec-compatible barriers are 12-mil or 20-mil reinforced polyethylene, always marked. We also carry Reflectix radiant barrier products for crawl space applications where downward heat loss is the primary concern rather than ground moisture. Topside Attic Insulation Seguin is an independent service provider with no affiliation to Demilec; we source through regional distributors and install to manufacturer spec.

OEM versus aftermarket: for vapor barriers, aftermarket 12-mil reinforced poly from Johns Manville or CertainTeed performs identically to Demilec-branded roll stock at roughly 15% less material cost. For spray foam, we stick with Demilec’s Heatlok HFO for rim joist work because the HFO blowing agent meets Texas environmental compliance without the shrinkage issues we have seen in generic two-pound foams after three Guadalupe County summers.

Signs Your Demilec Crawl Space Encapsulation Is Failing

• Soft or cupped hardwood floors, especially in spring. When the vapor barrier tears at seams or the perimeter seal fails, ground moisture rises and gets trapped beneath finished flooring. In Seguin’s clay-heavy soils around McQueeney and New Berlin, this moisture can spike to 80% relative humidity in a crawl space within 48 hours after a hard rain.
• Musty odor that intensifies when the AC runs. Your ductwork likely runs through the crawl space, and if the encapsulation has gaps, the return side pulls that damp air straight into your living space. We find this most often in homes near the Guadalupe River floodplain where seasonal water tables shift.
• Visible condensation on ductwork or insulation. This means the dew point inside your crawl space is higher than the surface temperature of your HVAC components, a clear signal that the vapor barrier is no longer maintaining the sealed envelope Demilec systems are designed for.
• Sagging or separated vapor barrier at seams. Demilec-compatible 12-mil barriers should lie flat with overlapped, taped seams. If you’re seeing pooling water on top of the barrier, the ground seal has failed or the drainage mat beneath was omitted in the original install.
• Increased energy bills with no other explanation. A compromised rim joist seal lets outdoor air infiltrate directly into your conditioned envelope. We have documented blower-door readings jumping 800 CFM50 or more from crawl space leakage alone in Seguin’s older ranch homes near Kingsbury.

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Replacement Cost & What’s Included

Most full encapsulation replacements in Seguin fall between $3,800 and $7,200. A 1,200-square-foot crawl with good access, no standing water remediation, and intact drainage mat runs toward the lower end. A 2,400-square-foot space with rotted sill plates, active mold on floor joists, and a need for new sump pump integration pushes toward the upper range. We also handle partial repairs, typically $1,200 to $2,800, where only the vapor barrier or select rim joist bays need attention.

Every quote breaks out materials and labor separately. You get a written price before any work starts, per Haven Standard Clause 1, with no bracketed allowances or “plus materials” language. The scope specifies mil rating, tape type, foam thickness at rim joists, and whether we are installing a new dehumidifier or tying into existing HVAC. Our 365-Day Done Right Promise covers the installation; material warranties run 10 to 15 years depending on the vapor barrier manufacturer. Before-and-after blower-door readings are included on applicable jobs so you can verify the air sealing result in actual CFM50 numbers.

DIY or Call Us?

What you can safely check: walk your crawl space with a flashlight and look for torn vapor barrier, detached tape at seams, or foam that has pulled away from rim joists. Note any standing water or white mold bloom on joists. Take photos. That documentation is useful for any contractor you call.

Where DIY goes wrong: spray foam application requires respiratory protection, calibrated temperature control, and knowledge of how thick a pass can be before exothermic reaction causes fire risk or shrinkage. We have been called to Seguin homes where a homeowner’s two-inch pass of closed-cell foam cracked and pulled away from the sill plate within six months because the substrate was 52°F, not the 60°F Demilec specifies. Vapor barrier installation looks simple but requires precise overlap, mechanical fastening at walls, and sealed penetrations; gaps you cannot see from your belly-crawl position render the entire system ineffective. For the foam work specifically, we recommend a trained installer. Call (830) 549-6646 and we will walk through what you found, no charge for the conversation.

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