Vapor barrier thickness is a key attribute of a below-slab vapor barrier but it does not tell the whole story. Tune into this Stego IQ episode where Stego Technical Director Dan Marks provides some insight on all the key attributes that make up a high-performing under-slab vapor barrier which is puncture resistance, tensile strength, and most importantly permeance and longevity.
Video Transcription
Does thickness tell the whole story about a vapor barrier? This is Stego IQ.
Vapor Barrier Performance - Check Out What's Under the Hood
Specifying thickness for a vapor retarder is like specifying the size of a car to determine its performance. We want to know what's under the hood! Thickness is a decent indicator of general performance, but it doesn't give us specifics that we want and that we need to have for the performance of the product.
We want to know the engine -- and the engine for the vapor retarder or barrier is going to be its puncture resistance, its tensile strength, and -- most importantly -- its permeance and longevity.
Not All Plastics Are Created Equal
Not surprisingly, not all plastics are created equal. And not every plastic -- even a high performance plastic -- is optimized to perform as an under-slab vapor retarder or barrier. If we were dealing in an industry where all the products had the same raw materials and the same design, thickness would be a good indicator of how well the product would perform. However, that is not the case.
The Minimum Requirements When It Comes to Vapor Barrier Thickness
If you look at the building code, IBC, the residential code, IRC, there are minimum requirements and it's good to make sure that we're at least satisfying those -- even though it's not the only thing we're looking for.
6-mil is an absolute minimum for the general residential building code, but for many years the Committee 302 of the American Concrete Institute (ACI) has recommended; "...that the thickness of the vapor retarder be no less that 10 mils (0.25mm)." In their most recent; "Guide to Concrete Floor and Slab Construction (ACI 302.1R-15)" Comittee 302 now recommends that the thickness and permeance of the vapor retarder material be selected on the basis of the protective needs of the materials being applied to the slab surface or the environment being protected, and the durability needed during and after installation.
With all that said, specification should not begin and end by meeting a minimum thickness. We also want to make sure the metrics and the performance match what we're trying to achieve. In this case: long-term water vapor protection.
The Key Performance Attributes to Ensure a Good Building Design
Rather than specifying or selecting vapor retarders and barriers based on thickness, project teams should select performance criteria that match their needs and are engineered and optimized for protecting the floor coverings, stored goods and building environment that they're designed to protect.
We want to make sure that the permeance rating is low enough that our floor coverings, stored goods and indoor air quality are not adversely affected. We want to make sure that the product is going to maintain these characteristics -- specifically the permeance rating -- for as long as we need it to.
And yes, we want to make sure that the material is durable enough to be installed effectively in the first place, and can withstand the potential construction traffic.
Again, thickness is not necessarily the criterion were concerned about. We want to make sure the metrics and the performance match what we need.
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