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The Your Crawlspace Vapor Barrier - a Review

John Krigger, founder and president of Saturn Resource Management, recently posted an article titled “Fixing Wet Crawlspaces with Plastic Sheeting” and said some very kind words about our patented Crawl Curtain. John is a building scientist, author, and energy expert who does training and is considered one of the top energy efficiency experts in the US by the likes of BPI, RESNET, and the US Department of Energy. The folks at Saturn Resource Management have made contributions to Residential Energy Services Network (RESNET), the Building Performance Institute (BPI), and the DOE’s Weatherization Assistance Program (WAP) to develop industry leading courses and publications.

John’s Blog reviews our approach to crawlspace vapor barriers as a means to control crawlspace moisture and says some very flattering things about our approach and products. It’s a proven fact that most of the air we breathe originates in the crawlspace. Drawn from the crawlspace by a phenomenon called the stack effect, air containing mold and mildew spores, toxic soil gasses, dust mites and other insects, and nasty odors makes its way into a home’s living space where it’s breathed by the home’s occupants. This unhealthy air aggravates allergies, damages a home’s foundation, and creates a generally unhealthy environment

Building scientists all agree the solution for better air quality starts with a quality vapor barrier. They all agree that the vapor barrier needs to be attached and sealed to the foundation wall. This recommendation is included in publications of The Environmental Protection Agency, The Department of Energy, Oak Ridge National Laboratory, The ZEBRAlliance, Dow Chemical Company, Numerous State Weatherization Offices, The 2000 through the 2012 versions of the Energy Code (IECC) all state, “The edges of the vapor retarder shall extend at least 6 inches up the stem wall and shall be attached and sealed to the stem wall.”

Forty seven of the 50 United States has adopted one of the energy codes, Attaching and sealing the vapor barrier to the stem wall has always been problematic. There are no adhesives that we know of that are effective with a Class I polyethylene vapor barrier. Mechanical fasteners add hours to a typical installation. And even with mechanical fasteners, the companies that recommend them require a combination of expensive sealing tapes, furring strips, caulks, specialized (and also expensive) nail guns, and hammer drills and plastic inserts. Not only are these installation techniques labor intensive, they can also damage the foundation wall.

The Your Crawlspace Crawl Curtain is the only practical alternative. More than anything else, John Krigger praised the Crawl Curtain for its simplicity and safety. Whether doing a full encapsulation or merely installing a standard, high quality vapor barrier, the Crawl Curtain installs in one simple step. Run a ¼” bead of our recommended polyurethane construction adhesive along the top of the wall and apply the Crawl Curtain. That’s it. You’re done. It is really that simple!

Since polyurethane cures rather than dries (like concrete), it only off-gasses harmless carbon dioxide. And since water is a catalyst for polyurethane to cure, the system will bond to even water saturated foundation walls. It is the ideal system for potentially damp crawlspace environments. The Crawl Curtain is a 9 mil coated fabric so it is strong enough to last the life of a house yet flexible enough to follow the contours and irregularities of a foundation wall. Installation contractors like it because it will seal any foundation wall including field stone. And because the Crawl Curtain installs without mechanical fasteners, it saves hours with no risk of damaging the foundation. Hours saved translates to money saved.

Since the stress on the Crawl Curtain is evenly spread along the entire perimeter of an installation, the polyurethane/Crawl Curtain bond is stronger than a mechanical fastener attachment with its individual connection points. The bond is so strong, it will support the weight of a 38 pound concrete block. Many contractors insulate crawlspace foundation walls with spray foam or rigid foam board.

The Crawl Curtain is the ideal underlayment for any crawlspace wall insulation. Sealing the walls is recommended for both foam board and spray foam applications. Dow, the manufacturer of Thermax insulation recommends sealing the wall prior to installing their product. And, used alone, even closed cell spray foam is only a Class II vapor retarder. So the Crawl Curtain is an ideal underlayment for any insulation application. 

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