Installing a crawlspace vapor barrier is not rocket science. It is not physically difficult. Whether installing a quality vapor barrier in a vented crawlspace or doing a complete crawlspace encapsulation, it only takes a little time, a little patience and a willingness to crawl around on your hands and knees for a couple of days.
Where to Buy a Crawlspace Vapor Barrier
There are many places to purchase a crawlspace vapor barrier. An on-line search will provide contact information many retailers. And the products they offer vary from inexpensive clear plastic to woven and coated fabrics much like swimming pool liners. The inexpensive liners can also be purchased from many hardware stores and home centers.
What Vapor Barriers Are Available
The inexpensive vapor barriers will do the job but it’s been our experience that they tear easily, don’t stay in place, and become brittle and crack after four to five years. But they are inexpensive.
The alternative is to spend a couple times more initially and purchase a product with a twenty five year warranty. The reinforced or woven products require no more time to install than the inexpensive shorter-lived products.
The real question is whether an installer wants to spend a couple of days crawling around in a damp crawlspace every four or five years, or wants to spend a little more initially and have an installation that is maintenance-free and will last for decades. Personally, it makes more sense to me to do it right the first time and be done with it.
Installing the Vapor Barrier
Whether doing a full crawlspace encapsulation or simply installing a vapor barrier in a vented crawl space, the installation of all products have a lot in common.
First, the floor needs to be completely covered, with all seams overlapped 6″ to 12″ and sealed with tape. While duct tape is a wonderful product with countless uses, it does not do a good job sealing the seams of a vapor barrier. A quality, water-proof vinyl tape designed specifically for sealing the seams is recommended.
Wrapping the Crawlspace Piers
Second, the floor material needs to be sealed around all the foundation supports. Whether steel posts or concrete block piers, it is necessary to prevent the migration of water vapor from around the foundation supports. This is usually done by wrapping the piers – sealing the piers with the vapor barrier 6″ to 12″ up from the floor. This provides a sealed pier to which the floor material can be sealed to using seam tape.
Wrapping the piers can be a little problematic. No safe, nonflammable, nontoxic construction adhesive is effective with the available materials except for a newly developed, patented proprietary wall and pier liner. The vapor barrier is typically applied to the piers using a combination of tape, mastic, caulk, and mechanical fasteners. The mechanical fasteners require that holes be drilled into the piers using a masonry bit and hammer drill. This adds exponentially to the installation labor.
The patented wall and pier liner can be applied to most any surface using a low VOC and nontoxic construction adhesive. Being low VOC and nontoxic, it is nonflammable and safe to use in the confined area of a crawlspace. It can be safely installed in a fraction of the time. It is the only material of its kind and can be ordered from it manufacturer.
Sealing the Crawlspace Walls
Finally, regardless of whether you’re installing a vapor barrier in a vented crawlspace or doing a full encapsulation, it is necessary to seal the floor material to the crawlspace walls. Most experts agree that this is a vital step for a well installed barrier or encapsulation.
If installing a vapor barrier, the floor material should be sealed to the wall 6″ to 12″ above the outside grade. Like wrapping the piers, most companies recommend the tape-caulk-mechanical fastener combination. The mechanical fasteners should be placed every two to three feet long the perimeter of the crawlspace. If taking this approach, be sure to use a respirator as concrete dust can cause severe respiratory problems.
If doing a full encapsulation, the entire wall, a minimum of three inches down from the sill plate to allow for a pest control inspection, should be sealed. Enough floor material can be purchased to extend up the walls or, the method we’ve found easiest, the wall is covered and sealed with a wall liner and the floor material is sealed to the wall liner using seam tape. Regardless of which method you use, the vapor barrier must be securely attached and sealed to the wall.
The manufacturer of the pier wrap also makes a patented wall liner that attaches to and seals the wall in one simple step. It reduces installation time by several hours. Like the pier wrap, it is available from the manufacturer.