Johns Manville Crawl Space Encapsulation Nationwide

Johns Manville Crawl Space Encapsulation: The Round Rock Owner’s Guide

We stock and install Johns Manville-compatible crawl space encapsulation systems in Round Rock, with most full encapsulations running between $3,800 and $7,200 depending on crawl space square footage and whether the foundation needs active dehumidification tied into the vapor barrier. Same-day assessments are available, and we carry JM membrane rolls and seam tape on our trucks for jobs up to 1,500 square feet. Most Round Rock homeowners realize their encapsulation is compromised when they notice a sharp musty smell returning after months of absence, or when their dehumidifier runs continuously without pulling the relative humidity below 65% - both point to vapor barrier breaches, failed seam seals, or membrane degradation at the foundation walls where Texas clay soil expansion creates abrasion points.

Call (737) 259-7528

Which Johns Manville Models This Applies To

Johns Manville produces crawl space vapor barrier membranes under their PermaRol and CrawlShield product lines, with thicknesses ranging from 6-mil utility-grade to 16-mil reinforced woven polyethylene. The critical spec is permeance rating - a measure of how much moisture vapor passes through the material in a 24-hour period. JM’s 12-mil reinforced barrier runs about 0.03 perms, which is what we specify for Williamson County’s clay-heavy soils where ground moisture pressure runs higher than in sandy east Texas counties.

To identify your existing JM membrane, check the white print line running every 24 inches along the roll edge - it lists the ASTM E1745 class (A, B, or C), the mil thickness, and the manufacturing date. Class A is required by Round Rock building code for conditioned crawl spaces; if your existing barrier is Class B or unmarked, it was likely installed before the 2018 IRC adoption or by a contractor who cut specification corners. We do not install below Class A in Round Rock.

Topside Attic Insulation Round Rock is an independent service provider - not affiliated with Johns Manville - and we source JM materials through authorized regional distributors. We also stock Reflectix radiant barrier products for hybrid encapsulation systems where the homeowner wants both vapor control and thermal reflection at the foundation walls.

Signs Your Johns Manville Crawl Space Encapsulation Is Failing

• Musty odor returning in conditioned air. When the vapor barrier tears at piers or perimeter walls, ground moisture re-enters the crawl space envelope and gets drawn into the HVAC return plenum. We see this most often in Round Rock’s Forest Creek and Brushy Creek neighborhoods where seasonal clay shrink-swell shifts the piers.
• Dehumidifier running 18+ hours daily with no humidity drop. The unit is fighting an unsealed moisture load. Check the condensate bucket - if it’s filling but the crawl space humidity stays above 60%, the barrier has a breach larger than the dehumidifier’s capacity.
• White mineral deposits (efflorescence) on block walls above the barrier line. This means moisture is wicking through the masonry and evaporating into the crawl space air - the barrier isn’t lapped high enough or the wall sealant has detached from the CMU.
• Sagging or pooled areas on the membrane surface. Standing water on top of the barrier indicates either a plumbing leak or, more commonly, that the membrane was installed without proper slope to a drainage point. JM’s 12-mil and thicker products handle foot traffic during service; 6-mil tears under a technician’s knee.
• Increasing energy bills with no HVAC changes. A failed encapsulation lets humid air infiltrate, and your air conditioner works harder to dehumidify the load. In Round Rock’s July-August stretch, we’ve measured crawl spaces at 78% relative humidity with breached barriers - the HVAC system is essentially conditioning outdoor air.

Replacement Cost & What’s Included

For a typical Round Rock crawl space between 1,000 and 1,800 square feet, full Johns Manville encapsulation replacement runs $3,800 to $7,200 installed. The lower end covers membrane-only replacement with existing dehumidifier reuse; the upper end includes new 12-mil JM reinforced barrier, foundation wall sealing with closed-cell spray foam to 2 inches, pier wrapping, and a new Santa Fe or Aprilaire dehumidifier tied to condensate pump discharge.

What drives the range: crawl space height (belly-crawls take longer), number of piers to wrap, whether the rim joist needs air sealing before the wall foam goes in, and if we need to install a new sump or gravity drain. Every job gets a written price before work starts - Haven Standard Clause 1 - and includes our Documented Photo Record showing the before condition, the seam overlap pattern (JM specifies 12-inch overlaps, we photograph each one), and the post-install blower-door reading if the crawl space is tied to the conditioned envelope. The 365-Day Done Right Promise covers all workmanship; JM’s material warranty runs 10 years against manufacturing defect.

DIY or Call Us?

Here’s what a Round Rock homeowner can safely check: verify the dehumidifier is set to 55% relative humidity and the condensate pump is discharging. Look for obvious membrane tears at access doors and pier bases. That’s the limit of useful DIY.

What goes wrong fast: cutting JM membrane to fit around piers without the proper overlap geometry, which channels water toward the wood rather than away. Using non-JM seam tape or construction adhesive that outgasses and delaminates in crawl space humidity. Installing a 6-mil utility membrane where 12-mil reinforced is code-required. And the big one - working in a crawl space without proper respirator protection when old fiberglass or rodent droppings are present. We’ve documented three jobs in Round Rock where a homeowner’s DIY attempt trapped moisture against the sill plate and accelerated decay.

Seal the leaks first. The insulation has nowhere to go until you do. Call (737) 259-7528 for a written assessment - estimates are free, and we bring the Johns Manville spec sheets so you can compare before deciding.

FAQs