Vapor Barrier Q&A

Tape for 6 mil Plastic Vapor Retarder?

Question: What tape is recommended for 6 mil Plastic Vapor Retarder?

Answer: We recommend a product we call Vapor Tape.  This tape is standard in 4” wide rolls, either 180’ or 210’ long.  This has a very aggressive adhesive system designed specifically to adhere to polyethylene sheeting.  The tape is designed to maintain the integrity of a vapor barrier application, and is normally used to seam the plastic to plastic joints.  For adhering the vapor retarder to protrusions and foundation walls, I recommend a reinforced Butyl Tape.  The Butyl Tape is standard in 1.5” x 100’ rolls.  This tape is amazing, because it remains permanently flexible, makes a watertight seal, and adheres to just about any surface.  I also recommend using Butyl Tape between overlapped sheets of vapor retarder as extra insurance against moisture intrusion.

Is 6 mil polyethylene classified as a Class 1 vapor retarder?

Question:  Is 6 mil polyethylene classified as a class 1 vapor retarder? What's the difference between Class 1,2,3 and Class A,B, and C?

Answer:  Some people use Class 1, 2, 3 interchangeably with A,B,C with all the certifications.  In the FR specs, one company calls their test results, which is identical to an ASTM test, class 1, 2, 3, where ASTM classifies theirs as Class A, B, C. 

6 mil Construction/Agricultural Grade Polyethylene does not pass any level of the ASTM E1745 Classifications for underslab varpor retarders in contact with soil or granular fill.  Generally engineered films should be used for this application, so they are made with 100% virgin resins, will not rot, or degrade, and are made to withstand the application.  Of the products we have on the market currently, none of the 6 mil products pass Class A, one has to go to the 10 mil engineered films, like VaporBlock 10 to pass this standard.

Is it better to put a plastic vapor barrier up over the concrete foundation walls when finishing a basement?

Question:  Is it better to put a plastic vapor barrier up over the concrete foundation walls when finishing a basement?

Answer:  Yes, ideally the top of the foundation wall should be covered with an engineered vapor retarder, such that moisture cannot transfer from the concrete foundation walls up into the wood through capillary action.

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How much vapor really gets into a home or building? Do I need a vapor retarder?

Question:  Do I need a vapor retarder/vapor barrier for my home? How much vapor really gets into a home?

 

Answer:  The amount of moisture entering a building through the slab on grade and foundation walls depends on the vapor pressure differential and the perm rating of the material(s) it must pass through. This value is known as the Water Vapor Transmission Rate ( WVTR ).

If you use construction and agricultural grade plastic sheeting (sometimes called, Visqueen) you don't really have much protection. This sheeting will degrade over time. The key is to get an ASTM E 1745 rated vapor retarder in place.

Adhering Plastic Vapor Barrior to Foundation Wall In Crawl Space

Question:  How do I adhere a plastic vapor barrier/retarder to a foundation wall in a crawl space?

Answer:  The best and most common way to adhere a vapor barrier to foundation walls is with a double sided butyl tape in combination with 1/4 inch plastic "Christmas tree" style push pins.

 
 
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