Crawlspace Vapor Barriers - Thick Enough?
Lately, I’ve been fielding a lot of questions about our Crawl Curtain vapor barrier designed for crawlspace wall applications. The most frequent question is about the thickness. Is 8 mils thick enough? Will 8 mils be strong enough to last? And is the Your Crawlspace vapor barrier adhesive strong enough?
The answer to all these questions is yes. When we developed the Crawl Curtain, a wall vapor barrier designed for crawlspaces, we extensively tested a number of different materials in a wide variety of possible situations that a contractor might encounter. We tested the current Your Crawlspace System in our offices and in hundreds of private residences and commercial buildings. Furthermore, the Your Crawlspace System was installed in many of the Advanced Energy System Vision houses built by Our Town Habitat for Humanity houses in the Charlotte, NC area and in several test houses built by the Department of Energy’s Oak Ridge Laboratories ZEBRAlliance.
In every case, the wall material installed easily, without problems, an exceeded expectations. In designing the Your Crawlspace vapor barrier system, we had a number of criteria. First and foremost, the system had to attach and seal on one simple step – without mechanical fasteners. Mechanical fasteners add hours to an installation. And simple physics tells you that an attachment at a single point with a Tapcon screw and washer, or a nail, or a plastic insert pressed into a predrilled hole creates a weak point that is likely to fail when put under any stress. It only makes sense that an attachment along the entire edge of the wall vapor barrier will be stronger. It spreads the stress over the entire edge rather than at a single point.
There are photos on our web site illustrating several forty pound concrete blocks that have been hanging from our crawl curtain for more than a year now with no attachment except for our recommended adhesive. So what about thickness? We tested materials ranging from 6 mils to 20 mils. The 8 mil Crawl Curtain thickness was not an arbitrary choice. First, the 8 mil thickness is plenty strong and puncture resistant for a crawlspace wall. Short of a clumsy plumber scraping the material and tearing it with tools or plumbing supplies, the material will last for years.
A crawlspace wall will receive virtually no wear, so 8 mils is plenty strong enough. Since crawlspace walls might be constructed of concrete block, brick, or field stone, we also wanted a vapor barrier that would conform to irregularities in the foundation wall. Our 8 mil Crawl Curtain attaches to a wide variety of irregular foundation substrates, sealing inside and outside corners and conforming to any irregularities encountered. It creates a simple, safe, and vapor proof seal.
