Johns Manville Crawl Space Encapsulation Nationwide

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

If you’ve got a Johns Manville crawl space encapsulation system that’s failed or failing, we stock the liner, tape, adhesives, and fasteners needed to repair or replace it, and we install throughout San Antonio for a typical range of $1,800 to $4,700 depending on square footage and how much of the old liner has torn away. Most repair jobs are done same-week, and a simple liner patch on a small San Antonio pier-and-beam can often happen same-day. You’ll usually find the problem the same way every homeowner does: musty smell drifting up through the floorboards, a spike in indoor humidity you can feel in the hallway, or you climb under the house to grab a storage bin and see the white Johns Manville liner sagging, torn, or puddled with water it was supposed to be keeping out. The liner itself is a tough product, but San Antonio’s clay-heavy soil shifts with every wet-dry cycle, and that movement is hard on anything fastened to a foundation wall.

Which Johns Manville Models This Applies To

Johns Manville makes encapsulation liner under a few different product lines, and most of what we see in San Antonio crawl spaces is their reinforced poly liner in 6-mil, 10-mil, and 12-mil thicknesses, sold in rolls that run 10 to 14 feet wide. You don’t need the exact original SKU to get a proper fix. What matters is thickness, width, and whether your crawl space has standing water or just damp soil. A 6-mil liner is fine for an older, dry vented crawl, but it is not what I would put back under a San Antonio home where the soil holds moisture for weeks after a rain. We carry Johns Manville-compatible liner and also work with equivalent 10-mil and 12-mil reinforced poly, plus the two-sided seam tape and mechanical fasteners Johns Manville recommends for their system. If you want to know what was originally installed, look for the printed brand marking on the liner itself, usually near a seam or up the foundation wall. One gotcha we see often: a homeowner buys a roll of 10-mil liner thinking thicker always wins, but their existing liner is heat-welded at the seams and the new one is tape-seamed, and the two don’t bond cleanly. Matching the seam method matters as much as the mil thickness. We stock tape-seam equipment on the truck for that reason.

Signs Your Johns Manville Crawl Space Encapsulation Is Failing

• Musty or earthy smell rising through the floors. The liner has torn, or a seam has opened, and moist soil air is now moving up through the floor assembly into your living space. The crawl space is supposed to be sealed off from the house; a tear breaks that barrier.
• Condensation on ductwork or floor joists under the house. When the liner fails, warm humid San Antonio air reaches the cooler surfaces under the floor and condenses there. Water dripping from joists is a sign the encapsulation is no longer doing its job.
• Standing water on top of the liner instead of under it. This usually means the liner was installed without the right slope or drainage, and water is now pooling where you can see it. A proper Johns Manville install directs water below the liner and toward a sump or drain.
• Visible tears, pulled fasteners, or liner sagging from the foundation wall. Clay soil movement plus the weight of any water that did get on top creates strain at fastening points. Once fasteners pull out, the liner starts peeling away in sheets.
• Insulation falling from the subfloor above. When humidity rises in the crawl space, fiberglass batts in the floor joists absorb moisture and get heavy, and the support wires or staples let go. It looks like an insulation problem, but the cause is the failed encapsulation below it.

Replacement Cost & What’s Included

For a typical San Antonio crawl space in the 1,200 to 1,800 square-foot range, a full liner replacement using Johns Manville-compatible 10-mil reinforced poly runs $2,200 to $3,900 installed. A small repair, like re-taping a 10-foot seam or patching a tear, is usually $350 to $700. A complete system with new liner, seam tape, fasteners, and re-attaching all wall terminations on a larger or tighter crawl runs up to $4,700. What drives the range is access: if the crawl has 18 inches of clearance and the old liner comes out in one piece, that is a faster job than a belly crawl where every piece has to be cut and dragged. Every quote we give includes the liner, tape, fasteners, labor, and removal of the old material. You get one written number before we touch anything under the house, and the work is covered by our 365-Day Done Right Promise. If a seam opens or a wall termination fails within a year, we come back and make it right, no debate.

DIY or Call Us?

A homeowner can safely do a visual check: look for tears, pooled water, sagging wall terminations, and whether the liner is still fastened around piers and at the foundation wall. That inspection costs you nothing and gives you a clear picture before anyone quotes a repair. What I would not recommend doing yourself is any work in a crawl space with standing water, exposed wiring, or a sewer line that has ever leaked. Moisture plus sharp fasteners plus a tight space is a bad combination, and most San Antonio pier-and-beam crawls have at least one surprise under them. The tape-seaming in particular is unforgiving: if the surfaces are not perfectly clean and dry, the seam fails within months, and you are back under the house again. If you want it done once, with a written price and a one-year workmanship guarantee behind it, call (903) 437-9164 and we’ll send someone out to measure. Tell me what’s in that room, and I’ll tell you exactly what goes on the other side of the wall.

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