AARST_Radon_Reporter_July_2023

THE RADON REPORTER | 23 MITIGATION Choosing the “Right” Vapor Barrier By Dawn Oggier In the realm of radon and other soil gases, vapor barriers (soil gas retarder membranes) play a vital role in protecting occupants and buildings by impeding movement of moisture vapor. Vapor barriers help maintain the desired indoor environmental conditions such as humidity and improve energy efficiency. Vapor barriers are typically made of plastic films such as polyethylene. There are many on the market to choose from and in this article we are going to wade through what you need to know to choose the “right” vapor barrier: terms such as mil, puncture resistance, tensile strength and permeance and ASTM E1745 Standard(s) to identify the puncture resistance, tensile strength and permeance ratings required to satisfy the ANSI/AARST Standard(s). First up is “mil.” There is a common belief that the thicker the mil, the more robust the barrier. The term “mil” is a unit of measurement equal to “one-thousandth of an inch or .001 inches.” When you see a vapor barrier described as, for example, “6 mil,” it means the thickness of the plastic film is 0.006 inches. This is the most common allowable thickness in building codes and other standards. Using mil as the only criterion for strength may be short-sighted because it doesn’t take into consideration the wide array of 6-mil barriers on the market with varying puncture, tensile and permeance ratings, all of which matter when talking about protecting occupants from radon. The ASTM E1745 standard has criteria for puncture resistance. Puncture resistance refers to the ability of a material to withstand the penetration of sharp objects or forces without tearing or puncturing. Puncture resistance is typically calculated in grams according to the ASTM D1709 Standard Test Method for Impact Resistance of Plastic Film by the Free-Falling Dart Method. In this test, a dart of a specified weight and shape is dropped from a certain height onto a sample of the vapor barrier. When the dart penetrates the film, the energy required to puncture the barrier is measured. The higher the energy (gram weight) required for puncture, the greater the puncture resistance of the vapor barrier. ASTM E1745 also specifies requirements for tensile strength, elongation, and tear resistance. These properties determine the material’s ability to resist stretching, tearing, or breaking when subjected to mechanical stresses. Tensile strength is typically measured using standardized tests, such as ASTM D882. During the test, a sample of the vapor barrier material is subjected to controlled tension until it reaches its breaking point. The maximum force or stress the material can withstand before breaking is recorded as tensile strength. ASTM E1745 permeance rating refers to the measure of a material’s ability to allow the passage of water vapor or moisture. Permeance is typically expressed in units of perms (permeability). A perm represents the amount of water vapor that can pass through a square foot of material in one hour with a specific vapor pressure difference. In the context of vapor barriers, permeance is an important characteristic as it indicates how resistant the barrier is to the movement of moisture vapor. The American Society of Testing and Materials developed ASTM E1745 to provide guidelines for selection, installation requirements for continuity, guidelines for sealing joints, overlaps, penetrations, and inspection of vapor barriers. ASTM E1745 specifies performance criteria for plastic water vapor retarders used in contact with soil or granular fill under concrete slabs. The standard outlines the physical properties that vapor barriers must possess, such as strength, flexibility, and resistance to moisture penetration. After measurement, the vapor barrier is given one of three classifications: Class A - Maximum of 0.1 perms, minimum 45 lb./in tensile strength, minimum 2200 grams puncture resistance. Class B - Maximum of 0.1 perms, minimum 30 lb./in tensile strength, minimum 1700 grams puncture resistance. Class C - Maximum of 0.1 perms, minimum 13.6 lb./in tensile strength, minimum 475 grams puncture resistance. The ASTM E1745 Standard has been incorporated into the ANSI/AARST all Radon / Soil Gas Mitigation Standards. Radon Professionals understand that choosing the “right” vapor barrier not only complies with the ANSI/AARST Standards but more importantly protects occupants against the dangers of radon gas, saving lives.