How do I select the right vapor encapsulation barrier?
Crawlspace radon systems are some of the toughest jobs, and yet they’re some of the most affordable for homeowners. Why is that? In short, marketing and consumer demand. A “vapor encapsulation system” often costs upwards of $5 per square foot. A “radon mitigation system” in that same crawlspace will often be closer to $1. In this post, I hope to show you why these two systems are more equal than you might think, and why many buyers are misinformed due to dated information.
“I need a 20 mil barrier”. I hear this from contractors—at the behest of homeowners—all the time. Why is the mil thickness the only deciding factor for the buyer? Unless your crawlspace is a landfill or brownfield site (what most 20 mil barriers are made for), then you probably don’t need more than 10. And if you are covering that: may I suggest moving instead??
Using MIL (millimeter thickness) to select a crawlspace encapsulation barrier is a lot like using “number of cylinders” to select a new car. It’s dated. What you really want to focus on is technical data sheet points like: puncture resistance; tensile strength; and permeance—permeance being the most important because after all, aren’t you trying to keep radon and water vapor out of your home? Modern 6 mil barriers perform better than many 20 mil barriers from just a few decades ago. See links at the bottom of this page for more.
Why is a properly installed radon system better than a vapor encapsulation system? Radon systems exhaust radon gas and in the process they exhaust gallons of water vapor each day. An encapsulated crawlspace does just that: it captures the moisture and tries to block it out. This is often ineffective (as we’ve seen time and time again: radon cannot be blocked out; it must be provided a new pathway outside the home). A radon system, while moving moisture and radon gas, often gets rid of “musty smells” too. Try it: next time you power up a radon fan, do a smell test 10-15 minutes later and see the difference in the lowest levels of your home!
So, what should homeowners really be asking?
What is the permanence rating of your barrier? What is its ASTM classification (use CLASS A)? Do you mechanically fasten the barrier to the walls?
Getting back to my original premise. Many radon contractors skip a crucial step–which is why homeowners get such a good price on their systems. Lots of radon pros do not mechanically fasten the barrier to the wall. Mechanical fastening can be done with “ramset”, with wooden 2x4s, or with christmas tree pins–to name a few methods. Mechanical fastening not only makes your system look better, it makes it hold up over time. Simply slapping a barrier up the wall with caulking doesn’t look very appealing and has the potential to be torn off over time.
I would choose a mechanically fastened CLASS A vapor barrier with a radon exhaust, over a 20 mil “encapsulation” every, single time.
Please visit the links on this page as well as my how to guides page for more information and demo videos. Choose a certified radon pro that follows AARST/ANSI guidelines and you’ll find you get a better system at a fraction of the cost!
