Johns Manville Crawl Space Encapsulation Nationwide

Johns Manville Crawl Space Encapsulation: The San Antonio Owner’s Guide

If you have a Johns Manville crawl space encapsulation liner that’s torn, sagging, or pulling away from the foundation walls, we stock and install compatible Johns Manville vapor barrier materials throughout San Antonio, typically same week if not same day. Most full crawl space encapsulation repairs in San Antonio run $1,800 to $4,600 depending on square footage, how much liner needs replacing, and whether your existing JM seam tape has failed. You usually discover the problem the same way every homeowner does: a musty smell that won’t quit, higher humidity upstairs, or you duck under the house for a filter change and see the liner drooping off the piers like a wet tarp.

Call (254) 279-0971

What matters with Johns Manville specifically is knowing which liner you have, because they’ve made several grades over the years and they don’t all behave the same way in San Antonio’s clay-heavy, humidity-prone crawl space conditions.

Which Johns Manville Models This Applies To

Johns Manville markets its crawl space encapsulation under a few different names depending on the year it was installed. The most common we see in San Antonio homes are the JM 10-mil and 12-mil reinforced polyethylene liners sold through their building products line, often paired with JM’s white acrylic seam tape and butyl adhesive for foundation-wall attachment. Some older San Antonio homes have the thinner 6-mil JM barrier that was never really meant for full encapsulation but got installed anyway in the early 2000s.

Here’s the compatibility gotcha: Johns Manville does not make a “crawl space encapsulation kit” the way some direct-to-consumer brands do. Their liner material is sold in bulk rolls to contractors, which means the “part” that failed on your house is really three things working together: the liner itself, the seam tape bonding it, and the mechanical fasteners or adhesive holding it to the concrete or CMU foundation wall. When one fails, the other two follow within a season or two. If you’ve got a JM liner that’s peeling at the wall line, replacing just the tape is a losing battle; the liner has usually shrunk slightly from San Antonio’s heat cycling and won’t re-bond cleanly. We carry both OEM Johns Manville liner and tape, and a compatible reinforced 12-mil alternative when a heavier spec makes more sense for your floor plan.

Signs Your Johns Manville Crawl Space Encapsulation Is Failing

• Liner sagging or pooling water between piers. This is the classic first sign. The JM liner has torn at a seam or pulled away from a wall, letting groundwater wick up and collect on top of the barrier instead of underneath it.
• Musty odor in the living space that gets worse after rain. A breached liner lets soil moisture evaporate directly into your floor assembly. In San Antonio’s late-summer thunderstorms, this smell becomes impossible to ignore.
• Visible mold staining on floor joists or subfloor sheathing. Once the barrier is open, relative humidity under the house spikes past 70%, and San Antonio’s clay soil holds moisture for weeks after a good rain. The joists are the first to show it.
• Seam tape curling or splitting at the edges. JM’s acrylic tape degrades from heat and humidity cycling. If you see the tape lifting anywhere, the seal is already compromised even if the liner looks fine in the middle of the field.
• Insulation falling from the floor cavities above. When the crawl space gets damp enough, fiberglass batts or spray foam detach from the subfloor. The liner failure caused that, not the insulation itself.

Replacement Cost & What’s Included

In San Antonio, a partial Johns Manville crawl space encapsulation repair (new liner in a damaged section, fresh seam tape, re-fastened wall attachments) typically lands between $1,800 and $2,900 for a standard 1,200 to 1,800 square foot crawl space. A full liner replacement with reinforced 12-mil material and complete wall re-attachment runs $3,200 to $4,600. The spread comes down to three things: crawl space height (lower means slower work), how much old material we’re hauling out, and whether your foundation wall condition requires a different fastening method.

Every quote is a written price before we start, and every repair carries our 365-Day Done Right Promise plus a free second visit if anything fails in that first year. You’ll know the number before a single roll gets unloaded from the truck.

DIY or Call Us?

You can safely inspect your Johns Manville liner yourself: look for tears along the piers, lifted tape seams, and standing water that shouldn’t be there. That’s real information and it’ll help you describe the problem when you call us. What you shouldn’t do is attempt a full re-liner yourself in a tight San Antonio crawl space. The combination of confined quarters, sharp debris hidden under the old liner, and the physical strain of pulling 100-pound rolls through a 30-inch access hatch is how homeowners end up with back injuries and a half-finished job that leaks worse than the original.

If the liner is torn in a small, flat section far from the walls and you want a temporary fix, a JM patch kit applied with proper seam primer will hold for a season. But if the problem is at the wall line or the seams, call us at (254) 279-0971. We’ll come out, look at the actual condition under your house, and give you a straight answer with a written price.

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