Johns Manville Crawl Space Encapsulation Nationwide

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

We stock and install Johns Manville-compatible crawl space encapsulation systems in Boerne, with most full encapsulations running $3,800-$7,200 depending on crawl footprint, existing moisture damage, and whether the foundation needs perimeter sealing first. Same-day assessments are available, and we carry JM vapor barrier rolls, seam tape, and mechanical fasteners on every truck. Most Boerne homeowners realize their encapsulation has failed when they notice musty odors returning after a rain, find fiberglass batts sagging between joists, or spot condensation beading on ductwork in May when the Hill Country humidity climbs.

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Which Johns Manville Models This Applies To

Johns Manville doesn’t sell encapsulation as a branded “system” the way some competitors do. Instead, they manufacture the component materials that contractors like us build systems from: Permaliner vapor barriers in 6-mil, 10-mil, and 16-mil thicknesses; Linacoustic RC duct liner for conditioned crawl applications; and Insul-Lock DS pipe insulation for mechanical runs below grade. The critical identification point is the mil rating stamped on the vapor barrier edge, not a model number. We’ve found 10-mil Permaliner in roughly 60% of Boerne homes built between 2005 and 2018, usually installed directly over bare soil with minimal seam treatment.

When we evaluate a JM-based encapsulation, we check whether the original installer used JM’s double-sided seam tape or generic hardware-store tape, which fails in 3-4 years in our clay-heavy Boerne soils. OEM Johns Manville tape is polyethylene-backed and rated for soil contact; aftermarket equivalents often delaminate where groundwater wicks upward. We stock both OEM JM materials and compatible alternatives from Reflectix, but we specify which we’re using and why in the written scope.

Signs Your Johns Manville Crawl Space Encapsulation Is Failing

• Condensation on ductwork or plumbing. When the vapor barrier tears at seams or pulls from foundation walls, warm humid air contacts cool surfaces below your floor. In Boerne, this accelerates in April and October when ground temperatures lag behind air temperatures by 15-20 degrees.
• Sagging or fallen insulation between joists. Fiberglass batts absorb moisture once the encapsulation fails, becoming heavy enough to drop from friction-fit hangers. We regularly find this in homes near the Cibolo Creek drainage where seasonal water tables run higher.
• Musty odors that worsen after rain. A functioning encapsulation should isolate crawl space air from soil moisture. If you smell earthiness within 48 hours of precipitation, the barrier has likely breached at a seam or penetration.
• Increased energy bills without thermostat changes. Wet insulation loses R-value rapidly; saturated fiberglass can drop from R-19 to below R-5. Your HVAC works harder to compensate, and the blower-door numbers we take before and after encapsulation typically show 300-600 CFM50 reduction when done properly.
• Visible mold on floor joists or subfloor. Surface mold appears at 70% relative humidity; a failed barrier lets crawl space RH climb well above that in summer. We document this with photos and include remediation scope in our written price before any work starts.

Replacement Cost & What’s Included

Full Johns Manville encapsulation replacement in Boerne typically ranges from $3,800 for a 1,200-square-foot crawl with straightforward access to $7,200 for 2,500+ square feet with active moisture issues requiring sump pump integration. The price includes removal of failed barrier and tape, surface prep, new 10-mil or 16-mil Permaliner installation with double-sealed seams, foundation wall sealing, and mechanical fastening at 6-inch intervals.

What moves the number: crawl height (less than 18 inches requires specialized equipment), existing mold remediation needs, and whether the rim joist needs closed-cell spray foam before barrier installation. We don’t blow insulation over an unsealed envelope; if your top plates and penetrations leak, we address that first. Every job closes with a Documented Photo Record and, where applicable, before-and-after blower-door readings. Our 365-Day Done Right Promise applies to all encapsulation work, backed by a written scope and warranty delivered before anyone starts.

DIY or Call Us?

There’s honest work a homeowner can do: verify the mil rating on existing barrier, photograph seam failures for documentation, and check that foundation vents are closed if the system was designed as conditioned. Where DIY goes wrong is in the prep. Proper encapsulation requires negative-pressure verification, soil gas testing in some Boerne zip codes, and mechanical fastening patterns that account for our expansive clay soils. We’ve been called to redo homeowner jobs where the barrier looked intact but was trapping moisture against sill plates because the grade wasn’t corrected first.

We carry Johns Manville and Reflectix materials on every truck, and we’ll give you a free second opinion on any written estimate you’ve already received. Call (830) 529-7780 for a written price before any work starts.

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