Johns Manville Crawl Space Encapsulation Nationwide

Johns Manville Crawl Space Encapsulation: The Leander Owner’s Guide

We stock and install Johns Manville-compatible crawl space encapsulation systems in Leander, with most full encapsulations running between $3,800 and $7,200 depending on crawl space square footage and whether the foundation needs active dehumidification. Same-day assessments are available, and we carry JM vapor barrier rolls, seam tape, and closed-cell spray foam on every truck. Most Leander homeowners discover their encapsulation has failed when they notice a musty smell returning after months of absence, or when their dehumidifier runs continuously without pulling the relative humidity below 60 percent. In older Leander subdivisions like Crystal Falls and Mason Hills, we regularly find JM 10-mil or 12-mil barriers that have pulled at the seams or developed punctures from routine plumbing access.

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Which Johns Manville Models This Applies To

Johns Manville does not sell crawl space encapsulation as a branded “system” the way some competitors do. Instead, they manufacture the component materials that contractors assemble in the field: poly vapor barriers in 6-mil, 10-mil, 12-mil, and 16-mil thicknesses; acrylic-based seam tape (JM 2000 series); and closed-cell SPF like Corbond III for rim joist and sill plate sealing. If your crawl space was encapsulated between 2015 and 2022, there’s a strong chance your contractor used JM 10-mil or 12-mil reinforced polyethylene, identifiable by the printed JM logo and mil rating running every 24 inches along the roll edge.

The critical compatibility gotcha in Leander’s Hill Country installations: JM 6-mil barrier was sometimes substituted by budget contractors during the 2018-2020 building boom, and it degrades to embrittlement in roughly 4-6 years here due to UV exposure through foundation vents and the thermal cycling between our 100°F August afternoons and 35°F January nights. We will not reinstall 6-mil. The 12-mil or 16-mil is the correct specification for a permanent encapsulation in this climate. We also stock Reflectix foil bubble insulation for rim joist applications where the original contractor used JM poly alone without addressing radiant heat transfer.

Topside Attic Insulation Leander is an independent service provider, not affiliated with Johns Manville. We source JM materials through standard distribution channels and will match any existing JM specification or upgrade it to a thicker mil rating if the original installation was undersized.

Signs Your Johns Manville Crawl Space Encapsulation Is Failing

• Musty odor returning in humid months. The vapor barrier has separated at seams or developed punctures, allowing soil moisture to evaporate into the crawl space air. In Leander, this typically surfaces in April through June when the clay soils release stored winter moisture.
• Dehumidifier running continuously without reaching setpoint. Your dehumidifier is sized correctly for the space, but the envelope is leaking faster than the unit can extract. We check this with a simple manometer reading at the access door.
• Visible condensation on ductwork or plumbing lines. The dew point in the crawl space has risen above the surface temperature of your HVAC ducts. This happens when the JM barrier has pulled away from piers or walls, creating unsealed gaps.
• Floor insulation sagging or falling. Fiberglass batts between joists absorb moisture when the encapsulation fails, then delaminate and drop. We see this most often in Leander homes built 2016-2019 with original builder-grade encapsulation.
• Pest activity increasing. Gaps in the barrier create access routes and humid harborage. The JM seam tape is the usual failure point here, it loses adhesion when applied over dusty concrete or in temperature swings beyond its rated range.

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After

Replacement Cost & What’s Included

For a typical Leander crawl space of 1,200 to 2,000 square feet, full JM encapsulation replacement runs $3,800 to $7,200 installed. The lower end assumes good access, intact dehumidifier, and standard 12-mil replacement. The upper end includes 16-mil barrier, new JM 2000 seam tape throughout, rim joist sealing with closed-cell foam, and a Santa Fe or Aprilaire dehumidifier if the existing unit is undersized or failed.

What drives the range: access clearance (less than 18 inches requires additional labor), number of piers to wrap and seal, whether the original barrier was glued to the walls (removal adds time), and whether we find unsealed plumbing penetrations or foundation vents that should have been blocked. Every job gets a Written Price Before Any Work Starts under Haven Standard Clause 1. The price you sign is the price you pay. Our 365-Day Done Right Promise covers all encapsulation work, and you receive a Documented Photo Record showing before condition, seam detail during installation, and final coverage verification.

DIY or Call Us?

There’s no high-tension danger in crawl space encapsulation like you’d find with garage door springs or electrical panels. The risk is different: you spend a Saturday cutting and taping poly, then discover six months later that your seams leaked because the concrete wasn’t properly cleaned and primed, or that you trapped moisture against the foundation by sealing over wet soil. We’ve pulled up homeowner-installed JM barrier in Leander that looked fine from the access but had 40 square feet of untreated mold on the soil side.

What you can safely check: verify your dehumidifier is running and draining, look for obvious tears or pulled seams with a flashlight, and measure humidity with a $15 hygrometer. What goes wrong in DIY: inadequate surface prep, wrong tape for the temperature range, missing pier wraps, and no verification that the space actually holds below 60% RH after sealing. We carry a digital manometer and calibrated moisture meters on every truck. Call (737) 252-7159 for a free assessment, we’ll show you exactly what failed and what it takes to fix it properly.

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