Johns Manville Crawl Space Encapsulation & Vapor Barrier Nationwide | Walt’s Insulation

Johns Manville Crawl Space Encapsulation & Vapor Barrier in San Antonio: What to Know First

If you own a home with Johns Manville crawl space materials and you’re seeing moisture, mold, or standing water, we can help. As an independent Johns Manville service provider here in San Antonio, we install and repair crawl space encapsulation and vapor barrier systems using Johns Manville products, usually within one to three days depending on crawl space size and condition. Most encapsulation jobs in San Antonio run $3,800 to $9,500 for a standard 1,200 to 2,000 square foot crawl space, and every estimate is free.

Call (866) 751-4428

This page is for San Antonio homeowners who already have Johns Manville products under the house or want to install them and need a straight answer about what works. Call (866) 751-4428 and you’ll get a live person, not a voicemail, 24/7.

How Johns Manville Products Fail - and How We Fix Them

Johns Manville makes solid crawl space materials, but South Texas humidity and clay soil push every product harder than most of the country. Here’s what we regularly see under San Antonio homes and how we address it.

• Johns Manville 6-mil poly vapor barrier tearing at ground level. The thin stuff doesn’t hold up to San Antonio’s rocky, caliche-heavy soil. Homeowners find rips along the seams and edges within a few years, which lets moisture migrate into the crawl space. We pull the torn 6-mil and replace it with Johns Manville’s 10-mil or 12-mil reinforced barrier, overlapping seams by 12 inches and running it up the foundation walls.
• JM ComfortTherm insulation falling off crawl space ceiling joists. This is a big one. The kraft or poly facing gets stapled, but in San Antonio’s humidity, the staples corrode and the batts sag. Moisture from exposed dirt makes the fiberglass heavier, and gravity does the rest. We remove the failed batts, address the moisture source first, then reinstall properly with support wires or switch to closed-cell spray foam if the crawl space is being fully encapsulated.
• JM CladStone or Formaldehyde-free fiberglass batts turning into a sponge. When a crawl space floods or has chronic high humidity, fiberglass absorbs water like a paper towel and doesn’t dry out easily in San Antonio’s hot, humid air. Mold follows. We don’t just replace the insulation. We find why water got in, fix the grade or drainage issue, then install new material only after the space is dry.
• Vapor barrier seams separating due to poor initial taping. Cheap tape or missing tape at the seams means the barrier fails even if the material itself is fine. We use Johns Manville’s seam tape or a higher-grade contractor tape and double-check every overlap. A barrier is only as good as its seams.
• JM Glasliner or similar duct-liner products degrading in vented crawl spaces. When insulation on ductwork gets damp, it corrodes the metal underneath. We see this in older San Antonio homes where HVAC ducts run through the crawl space. The fix often means pulling the old liner, treating any rust, and re-insulating with proper vapor sealing.

One thing we notice that Johns Manville’s own spec sheets won’t tell you: in San Antonio’s clay soil, the ground shifts seasonally. A barrier that was perfectly flat in March will have pulled away from piers by September. That’s why we insist on leaving slack at every support column and checking the barrier a year after install. It’s the kind of detail you only learn by doing this work here, not by reading a manual.

Our Johns Manville Crawl Space Encapsulation & Vapor Barrier Process

Every job follows the same sequence, whether it’s a repair or a full encapsulation. We don’t skip steps, and we don’t rush.

1. 1
   We inspect the crawl space. A technician crawls the entire space, checks moisture levels, identifies where water is coming from, and photographs everything. You get the photos, not just a verbal summary.
2. 2
   We give you a written estimate with two numbers. One for basic vapor barrier replacement and sealing, one for full encapsulation if you want it. The quote shows material costs, labor, and timeline. No surprise fees later.
3. 3
   We address water intrusion first. If grading, downspouts, or a plumbing leak is causing the moisture, that gets fixed before any barrier goes down. Putting plastic over a leak is a waste of your money.
4. 4
   We install Johns Manville barrier and insulation to spec. Whether it’s 10-mil, 12-mil, or a full ComfortTherm + barrier system, we follow Johns Manville’s installation guidelines so your warranty stays valid.
5. 5
   We seal and test. For full encapsulation, we seal vents with rigid foam board, tape all seams, and check for gaps with a thermal camera. Then we verify the moisture level drops before we call the job done.
6. 6
   We walk you through it and back it up. You see the finished space, we explain what was done, and the work is covered by our Done Right Promise: if it’s not done right, we make it right. No runaround.

What Johns Manville Crawl Space Encapsulation & Vapor Barrier Costs in San Antonio

Here’s what we typically charge in San Antonio, based on actual jobs we’ve done recently. Prices vary with crawl space size, access, and how much repair work is needed first.

• Vapor barrier replacement (10-mil) over 1,200 sq ft: $2,200 – $3,800
• Vapor barrier replacement (12-mil reinforced) over 1,500 sq ft: $3,000 – $5,200
• Full encapsulation with wall liner, vapor barrier, and vent sealing (1,500 sq ft): $5,500 – $8,700
• Insulation removal and replacement in crawl space (500-800 sq ft): $1,800 – $3,400
• Crawl space cleanout and debris removal before encapsulation: $400 – $900

What moves the price: crawl space height (if a tech can’t stand up, it takes longer), existing water damage, dead animals or pest debris, and whether you want standard batt insulation or spray foam for the rim joists. We give one written number and it doesn’t change unless you add work. Call (866) 751-4428 for a free estimate, and remember: no trip charge inside our service county.

Why San Antonio Homeowners Call Walt’s Insulation for Johns Manville Work

I’m Walt Brenner. I grew up on the north side of San Antonio, near Brackenridge Park, and I’ve been crawling under houses in this city since 2000. My team and I know what works in San Antonio’s climate because we’ve seen what fails. We install Johns Manville products because they hold up when installed right, but we also work with Owens Corning, CertainTeed, Knauf, and Reflectix for cases where a different material makes more sense for your specific crawl space. We’re not married to one brand. We’re married to doing it right.

Every call is answered by a live person, 24/7. Every technician who comes to your house is background-checked and in uniform. Every job carries our Done Right Promise for life. That’s not marketing language. It’s how we’ve run this business for over 25 years. We have a published address and license number, and we answer the phone live - talk to a real person, get a straight answer.

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