Vapor Barriers

Photo Credit: We Got You Covered - Commercial Building Roofing & Maintenance Services Ottawa


Improper installation resulting in mold is the leading source of health concerns when it comes to vapor barriers. However, it’s also important to understand the health implications of the material options when spec’ing vapor barriers. 


Vapor barriers are used in areas of a building prone to excess moisture. Factors such as geographic location and varying climate are important to consider to determine the need for and location of vapor barriers. Understanding the physics of this phenomenon is critical to create a healthy wall assembly.1


A costly concern that results from omitting vapor barriers is indoor air quality issues from mold and mildew growth. According to the EPA, once molds grow under ideal conditions, they can produce irritants, allergens, and mycotoxins. 2


Vapor Barrier Options:
The most common membrane products designed as vapor barriers and vapor retarders include polyethylene, nylon, and paper-based membranes.3


Polyethylene is considered a safe plastic and is not toxic to human health in its solid form.4 However, in its vapor or liquid form, it can be toxic during manufacturing if inhaled or absorbed into the skin.5 Polyethylene often goes unrecycled due to supply chain control issues and the low price of virgin resins.6 It is also important to consider the feedstock of these materials. Polyethylene uses natural gas instead of petroleum.7


Nylon, on the other hand, is primarily derived from petroleum.8 Petroleum based products contain toxic compounds which leach into the environment and enter our bodies, and have been linked to health problems such as cancer, learning disabilities, birth defects, and allergies.9 Nylon is also not biodegradable.8


Paper-based membranes are the only fully-recyclable option but may not be as durable as the the other alternatives.


“Smart” vapor barriers should be specified whenever possible. These products slow vapor diffusion in less-humid conditions while allowing drying when conditions are more humid, resulting in better performance than standard vapor barrier options.3


Applying the knowledge: 
When SPEC’ing vapor barriers, communicate the importance of proper installation to your contractor and consider the implications of your membrane options.  Be sure to ask manufacturers for transparency documentation before choosing the most appropriate option that meets project goals.


✓ Look for products that:

  • Specify brands and products that offer HPDs.
  • Specify Declare Red-List Free products.

 ✓ Be sure to:

  • Analyze the vapor profile of the building to understand use case.
  • Maintain a balance of permeability between layers of moisture barriers.
  • Use with a compatible air barrier or choose a water resistive barrier to combine vapor retarder and air barrier elements.

 ✗  Avoid:

  • Using poly, foil faced batts, reflective barrier foils, and vinyl wall coverings on the interior of air-conditioned assemblies.11