In the world of standards and processes for evaluating building materials, ASTM E96 stands out as an essential test for determining the water vapor transmission rate. Along with similar standards, ASTM E96 provides critical testing and assessment for a range of commercial products, including water resistive barriers (WRB), water resistive coatings, roofing underlayments, and vapor retarders such as spray foam insulation.

As a third-party testing agency, ICC NTA uses this standard to determine a material’s rate of water vapor transmission so that specifiers know whether or not a particular material will work in its intended end-use.


Permeance and PermeabilityASTM E96 Water Vapor Transmission Assessment

Water vapor transmission (WVT) testing determines both permeance and permeability. Permeance, measured in perms, is the time rate of water vapor transmission through unit area of flat material or assembly of materials induced by vapor pressure difference between two surfaces. Permeabilty, measured in perm inches, is the arithmetic product of permeance and thickness.

Watch a video about the ASTM E96 test method for more information on how WVT is determined.


Water and Desiccant Methods

Within ASTM E96, there are two methods for determining water vapor transmission rate: the desiccant method and the water method. These methods are also commonly referred to as ‘dry cup’ and ‘wet cup’ tests, respectively. Calcium chloride desiccant is used in the ‘dry cup’ method, whereas water is used in the ‘wet cup’ method. By analyzing the change in weight of the cups over time, we can determine the movement of water vapor through the test material.


Why It’s Important

This type of analysis is vital to help prevent situations that could allow moisture in places you don’t want it, like inside a wall cavity, which could lead to corrosion, rotting, or other detrimental conditions.

In a more general sense, different types of water-resistive barrier testing can also be helpful with forecasting how materials will stand up to water damage, especially as the 100-year storm phenomenon becomes more common. ASTM E96 contemplates environmental exposure that is widely important in determining how buildings stand up to pressure over time.

ICC NTA works with stakeholders to determine water vapor transmission rates and more for building materials. Performance standards like ASTM E96 are important for helping building product manufacturers, specifiers, Authorities Having Jurisdiction (AHJs), and the general public to evaluate materials for use in construction.

About ICC NTA, LLC: As an accredited third-party agency and part of the International Code Council (ICC) Family of Solutions, ICC NTA provides code evaluation, product certification, inspection, engineering, plan review, and testing services, as well as independent quality and standards compliance verification for building product manufacturers. With offices, testing labs, and training facilities in Nappanee, Indiana and Bryan, Texas, ICC NTA serves residential and commercial builders, code officials, manufacturers, and suppliers throughout the building industry.