Vapor Retarders


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8.5" x 11"
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Use this free downloadable 3-part SimpleSpecs™ master specification to specify vapor retarders to control moisture vapor transmission passage through the roof, wall, and floor floors.

As a construction professional, you are likely familiar with the many challenges that come with building and maintaining structures. One key factor to consider is the impact of moisture and water on the building materials and the overall stability of the structure. That’s where vapor retarder sheeting comes in.

What is a Vapor Retarder Sheeting?

A vapor retarder is a material used to prevent the movement of water vapor through building envelope components such as walls, floors, and ceilings. Vapor retarder sheeting is a type of vapor retarder that is made from a thin, flexible material and is installed as a barrier to prevent moisture migration in the building.

Why is Sheeting Important?

  • Protection against Moisture Damage: Vapor retarder sheeting helps prevent moisture from penetrating the building envelope and causing damage to the structure, insulation, and other materials. This is especially important in areas with high humidity or high levels of precipitation, where the risk of moisture damage is elevated.
  • Energy Efficiency: By preventing moisture from entering the building, vapor retarder sheeting can also help improve the energy efficiency of the structure. When moisture is present, it can cause the insulation to lose its effectiveness, leading to higher energy costs and lower comfort levels.
  • Improved Indoor Air Quality: Moisture can also contribute to indoor air quality problems, such as mold and mildew growth, which can pose health risks to building occupants. Vapor retarder sheeting helps prevent these problems by blocking moisture and keeping indoor air dry and clean.
  • Long-Term Durability: Proper installation of vapor retarder sheeting can help extend the life of the building and its components. By preventing moisture damage, the building will remain stable and secure, even in the face of harsh weather conditions.

What is a perm rate?

Permeance, also known as perm rate, is a measure of the ability of a material to allow water vapor to pass through it. In construction, permeance is used to evaluate the effectiveness of vapor retarders, such as vapor retarder sheeting.

ASTM E96 is a standard test method used to measure the permeance of materials, including vapor retarders. It is a widely recognized method for determining the permeance of a material and is used to compare the performance of different vapor retarders. The test involves exposing the material to a controlled environment, such as a laboratory, and measuring the rate of water vapor transmission through the material. The results of the test are expressed in perms, which is a unit of permeance.

Helpful tips:

  • The term vapor retarder defines a material with a moisture vapor transmission rate of less than one (1) perm. The term vapor barrier is often used to describe these plastics, but that is discouraged. As it is nearly impossible to construct an absolute barrier.
  • The design professional should take careful consideration of various factors to prevent condensation within the roof, wall, and floor assemblies. Climatic conditions including mean summer and winter temperatures and average relative humidity, both indoor and outdoor, can have a huge effect on moisture vapor movement. In addition, the location of the vapor retarder within the assembly is critical.
  • In order to be effective, the vapor retarder must be continuous. With joints sealed and the vapor retarder sealed around all penetrations and at the perimeter.

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