Building envelope essentials: The role of a water-resistive air barrier

Installing and specifying WRABs

Properly specified and installed WRABs can help protect a building envelope from premature decay, save energy, improve comfort, contribute to better air quality, and allow mechanical systems to perform optimally. Building designer’s should consider obtaining advice from building envelope experts, such as building science specialists or manufacturers’ technical representatives, when selecting materials for the building envelope.

Recent feedback from designers and installers of WRABs indicates the following list of the most requested performance features:

• Maximum compatibility with other products.
• High temperature stability of the installed material.
• Low temperature application of the material.
• Solutions for various UV exposures.
• Clear installation details and designer support.
• Material options to suit the project’s climate region and zone:

◦Permeable or non-permeable.

◦Self-adhered sheets or fluid applied.

Building codes and standards

What part do building codes and standards play in ensuring the design and installation of the WRABs are considered resilient? Simply put, they do not play a role. Many may argue it is not their responsibility to ensure resiliency—after all, codes and standards have always set reasonable minimum standards. They have done this by systematically evaluating the risks and these risks have always been based on historic experience and data when it comes to weather related events. Benchmarks, such as 50- or 100-year storms, have been considered reasonable and for the most part, accurate in determining guide minimums. However, there are many that believe the trajectory of climate events is on a very steep climb to examples not seen before, so how could codes and standards keep up with such change?

However, all is not lost. There is a growing consensus within the industry that it needs to do better, and there is a larger understanding among professionals that, although no one has a crystal ball, there is some valuable input being made into accurately predicting the events to come. Based on those models, at least there is understanding as to where things are heading, and allows for reasonable engineering judgements to be made in preparing for resiliency.³

Currently, there are default codes and standards in place. The following list of documents provides what is currently available as reference and guidance for the design, specification, installation, and testing of air barriers:

• National Building Code of Canada (NBC)

◦Provincial building codes

◦Part 9—Small buildings

◦Part 5—Environmental separation

• CAN/ULC-S741-08(R2020), Standard For Air Barrier Materials—Specification
• CAN/ULC-S742:2020, Standard For Air Barrier Assemblies—Specification
• ASTM E2178-21a, Standard Test Method for Determining Air Leakage Rate and Calculation of Air Permeance of Building Materials
• ASTM E2357-18, Standard Test Method for Determining Air Leakage of Air Barrier Assemblies
• ASTM E3158-18, Standard Test Method for Measuring The Air Leakage Rate of a Large or Multi-zone Building