ASTM (American Society for Testing and Materials) E1745 is the Standard Specification for Plastic Water Vapor Retarders Used in Contact with Soil or Granular Fill under Concrete Slabs. This standard requires products undergo conditioning testing designed to simulate in-service (under-slab and installation) conditions, and it classifies vapor retarders based on their tensile strength, puncture resistance, and water vapor permeance ratings.
ASTM E1745 is the standard for flexible sheet membranes to be used as vapor retarders for on-ground and below-grade slab applications under concrete. It requires that applicable products be tested to determine their tensile strength, puncture resistance, and water vapor permeance ratings, this final metric being measured both before and after undergoing mandatory conditioning testing.
Once these measurements are taken, the vapor retarder is given one of the following three classifications:
The required tests mentioned above utilize specific standard test methods:
Once you have a clear understanding of ASTM E1745, choosing a classification of vapor retarder for your project should be much simpler. However, there are drawbacks to the standard that need to be taken into account. For instance, maximum permeance rating requirements don’t change by class. Choosing a Class A vapor retarder does not necessarily guarantee sufficient protection; you may need to specify a permeance rating well below 0.1 perms. Also, ASTM D1709, while useful for determining puncture resistance, simulates only impact resistance and not the push-through or point loads caused by rocks or other sharp objects.
4 critical items to verify with the manufacturer prior to purchasing a vapor retarder are:
The quality of any construction project depends on three simple factors: good design, superior workmanship, and quality products. A product that also incorporates these principles will prove to have durability and functionality that exceed the design requirements. ASTM E1745 is an extremely useful standard for any specifier of under-slab vapor retarders and barriers. While it’s not a complete or comprehensive tool when creating specifications, it’s still an important component.
Under the 2021 International Residential Code (IRC®), it is required that water vapor retarders used beneath concrete floor slabs conform to the ASTM E1745 Class A specifications. This inclusion in the residential code emphasizes the necessity for higher-performance materials that offer more robust vapor protection at the first side of the home. Adhering to these requirements is not only crucial for meeting building codes but also for helping provide homeowners with a healthy and durable living environment.
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Editor's note: This blog post was initially written by Dan Marks, our former Technical Director at Stego, in October 2016 and has been revised to stay up-to-date.