Johns Manville Vapor Barrier Installation: The San Antonio Owner’s Guide
We stock and install Johns Manville vapor barrier materials throughout San Antonio, with most installations running between $1.50 and $3.75 per square foot depending on crawl space height, access, and whether we’re also handling encapsulation. Same-day and next-day appointments are available for most San Antonio neighborhoods, and our trucks carry Johns Manville 6-mil, 10-mil, and 12-mil poly sheeting along with seam tape and fasteners. Most homeowners discover their vapor barrier has failed when they notice a musty smell coming from the crawl space, higher indoor humidity, or visible moisture pooling on top of the plastic. In San Antonio’s clay-heavy soil and humid Gulf air, a torn or improperly overlapped barrier fails fast and starts affecting everything above it.
Key Takeaways
- We install Johns Manville vapor barriers in San Antonio, typically same-day or next-day
- Installed cost: $1.50 to $3.75 per square foot, with free estimates and no trip charge inside Bexar County
- 6-mil is a bare minimum in San Antonio; we recommend 10-mil or 12-mil for crawl spaces with any foot traffic or rocky soil
- Lifetime workmanship backed by the Done Right Promise
- We answer the phone live, 24/7 at (866) 751-4428
Which Johns Manville Models This Applies To
Johns Manville doesn’t sell vapor barriers under confusing model numbers the way an HVAC manufacturer might. The product line is straightforward: it’s a polyethylene sheeting system sold by thickness and roll width. You’ll find Johns Manville VaporBlock underlayment in 6-mil, 10-mil, and 15-mil, with 10-mil and 12-mil being the most common choices for San Antonio crawl spaces. The rolls come in widths from 8 to 20 feet, which matters when you’re trying to cover a crawl space with minimal seams. If you’re looking at an existing barrier and trying to identify it, the Johns Manville VaporBlock rolls have the brand name printed along the edge every few feet. For older installations, the printing may be faded or buried under dust, but you can measure the thickness with a micrometer to confirm what was originally installed.
The practical difference between the mil ratings in a San Antonio context is real. The 6-mil product is the code minimum in many jurisdictions, and it works fine in a crawl space nobody ever enters. But if you have a pier-and-beam house with a storage area underneath, or if your crawl space has exposed rock and construction debris, 6-mil tears under foot and around obstacles. We stock 10-mil and 12-mil on our trucks because those hold up to San Antonio’s rocky Hill Country pockets and the occasional plumbing repair that sends a contractor crawling through. Our crews also carry Johns Manville seam tape and proper mechanical fasteners, because taping seams with the wrong product is the fastest way to undo the entire installation.
We also stock Reflectix radiant barrier products for homeowners combining vapor control with heat reflection. Johns Manville and Reflectix don’t compete with each other; they solve different problems, and a San Antonio home often benefits from both.
Signs Your Johns Manville Vapor Barrier Installation Is Failing
- Musty or earthy smell in the house. When a vapor barrier fails, moisture moves freely from the soil into the crawl space and then into your living space. That damp-earth smell is the first thing most San Antonio owners notice, and it usually gets stronger in summer when the heat accelerates evaporation from exposed soil.
- Water pooling on top of the barrier. Some condensation is normal, but standing water sitting on the plastic means water is coming in from somewhere, whether that’s a drainage problem, a plumbing leak, or a seam that has separated. If you can see puddles from the crawl space entrance, the barrier is no longer doing its job.
- Sagging barrier that has pulled away from the foundation piers. In San Antonio’s clay soil, houses shift. Floor joists expand and contract with seasonal humidity changes, which pulls on the barrier fasteners. When sections detach from the piers, the barrier gaps open and moisture gets through. We see this more in older pier-and-beam homes in the Monte Vista and Alamo Heights areas.
- Visible rips, runs, or rodent damage. Rats and mice in San Antonio crawl spaces don’t care what brand of vapor barrier you paid for. If rodents have chewed through sections, you’re looking at a patch job that may not hold, depending on the location and extensiveness of the damage.
- Floor cupping, warping, or insulation that’s soaked. A failed vapor barrier means your subfloor and floor insulation are absorbing moisture they were never designed to handle. If your hardwood floors are cupping or the insulation in the floor cavities feels damp, the vapor barrier often gets the blame, and it’s usually earned.
Replacement Cost & What’s Included
For a typical San Antonio crawl space between 800 and 1,500 square feet, a Johns Manville vapor barrier installation runs $1,200 to $5,500 installed. That price includes removal and disposal of the old, failed barrier, site preparation, the new Johns Manville poly sheeting in your chosen thickness, seam taping, mechanical fastening to piers and perimeter walls, and a final inspection. The variables that push you higher are crawl space height (under 24 inches gets tight and slow), the amount of debris or standing water we need to address first, and whether you want full encapsulation with a white liner and taped wall coverage instead of a ground-only barrier.
| Scope | Price Range |
|---|---|
| Ground-only barrier, 800-1,200 sq ft (includes removal of old barrier) | $1,200 – $3,600 |
| Ground-only barrier, 1,200-2,000 sq ft | $2,400 – $5,500 |
| Full encapsulation (walls + piers + sealing), 800-1,200 sq ft | $4,800 – $9,000 |
| Barrier repair only (single seam or small tear) | $225 – $600 |
| Seam re-taping, per linear foot | $3.50 – $7 |
Every installation is covered by our Done Right Promise. Lifetime workmanship means if a seam fails or the barrier detaches because of an installation error, we come back and fix it. No argument, no runaround. That’s the entire point of the company I started in 2000, and it’s not changing.
DIY or Call Us?
Nobody dies installing a vapor barrier, so the safety conversation here is different from what we’d give you for a garage door spring or an electrical panel. The risks are more about doing it wrong and paying twice. What an owner can safely check from the crawl space entrance: whether you can see standing water, whether the barrier is visibly torn or detached, and whether the musty smell is coming from the crawl space at all. You don’t need a pro for that inspection, and we’ll answer questions about what you’re seeing over the phone at (866) 751-4428.
Where DIY goes sideways is in the crawl space itself. San Antonio crawl spaces in summer are brutally hot. Working on your belly in 110-degree humidity with spiders, snakes, and rodents isn’t a fun Saturday project. More importantly, if you don’t get the seams overlapped and taped correctly, don’t flash around the piers properly, or use the wrong tape, your new barrier will fail within a season or two, and you’ll be paying for the job twice. We see this all the time, a homeowner buys the Johns Manville roll thinking they’ve saved money, and two years later the floor is musty again and the insulation is soaked. The first time we show up, we fix it properly. Call us and we’ll give you a straight number.
FAQs
A properly installed Johns Manville 10-mil or 12-mil vapor barrier typically lasts 15 to 25 years in a San Antonio crawl space, while 6-mil often fails within 5 to 10 years because it tears under foot traffic and degrades faster in the heat. The barrier material itself is UV-stable, but the typical failure points in our climate are seams, fasteners around shifting piers, and rodent damage. Call (866) 751-4428 and we’ll inspect what you have before you spend money replacing something that still has life in it.
Yes, small tears under 12 inches can generally be repaired by cleaning the surface, overlapping a patch by at least 6 inches on all sides, and taping with a Johns Manville-compatible seam tape, and we quote repairs from $225 to $600. If the barrier is more than 10 years old, badly chewed by rodents, or pulling away in multiple sections, replacement is usually more cost-effective than chasing patches. We’ll give you an honest answer either way, and a free second opinion on any written estimate is always available.
For an average San Antonio crawl space, the installation usually takes one full day from setup to cleanup, though larger or fully encapsulated spaces can run two to three days. We schedule the work when you’re home for the initial walkthrough, and our background-checked, uniformed technicians handle everything from removal of the old barrier to a final walkthrough with you.
We stock Johns Manville 6-mil, 10-mil, and 12-mil poly sheeting, seam tape, and fasteners on our trucks, which means we can typically complete the work the same day we diagnose the problem. We also carry Reflectix products for homes where a radiant barrier would solve a separate problem from the vapor issue. If your job needs a specific roll width we don’t have on board, we’ll have it within 48 hours.
Talk to a Real Person in San Antonio
If you’ve got a failing Johns Manville vapor barrier and you need someone to look at it, call us at (866) 751-4428. We answer the phone live, 24/7. You’ll talk to a person who can schedule the visit, answer questions about pricing, and if we can’t help, tell you who can. Free estimates, no trip charge inside Bexar County, and $40 off any repair over $200. If you’ve already got a written estimate from another company, bring it to us for a free second opinion. And if you’re a senior or a veteran, there’s a permanent 10% discount, always. We’ve been doing this in San Antonio since 2000, and the one down the road is the one who’ll actually come back if something isn’t right.
Written by Walt Brenner, Owner, Walt’s Insulation, serving San Antonio and nearby areas.