A weather resistive barrier (WRB) certainly plays a key role in protecting the building envelope against air and moisture infiltration. It’s a best-practice component of any high-performance wall system. But is housewrap required by code?
The short answer? Yes. A weather resistive barrier has been a part of the International Residential Code since 2006 and has been widely accepted in local codes since then. But meeting bare minimums only tells part of the story.
How is Housewrap Required by Code?
Section R703.2 of the 2018 International Residential Code requires a WRB to continuously cover the wall behind the veneer/cladding and to be integrated with all penetrations and to provide a means of drainage to the exterior. A WRB is not required over concrete or masonry walls.
The minimum requirement for the WRB is No. 15 felt complying with ASTM D226, Type 1. The next option is a WRB that passes ASTM E2556, which evaluates tensile strength, water holdout, vapor permeability, and pliability testing. The International Code Council provides a service to ensure compliance with the changing codes by evaluating material properties, testing procedures, and installation requirements (ICC-ES AC38 – Acceptance Criteria for Water-resistive Barriers.) An assembly can also be tested under ASTM E331 to evaluate the integration of the WRB to the windows and other penetrations.
In addition, Section R703.4 – Flashing states that a flashing material, such as a tape or liquid-applied, must be shingle-overlapped and integrated with the WRB at all windows/doors per the manufacturer install guide.
Why Builders Should Think Beyond the Building Code
The building code represents the minimum requirement to pass inspection. In other words, code is a good—and necessary—starting point, but it is designed to be vague on details and product selection to allow builders the most freedom to make their own choices. To build homes that deliver the utmost in longevity and energy efficiency, it’s important to think beyond code minimums.
For example, code-compliant felt paper will not perform as well or last as long as a synthetic flat housewrap and definitely not as well as a drainable housewrap like HydroGap and others. HydroGap reduces moisture risk by allowing water to drain and keeping the wall dry. By building to a higher standard, we can create an assembly that will last much longer. For example, homes built to Passive House standards offer 90% energy savings and provide better comfort and indoor air quality.
Ideally, consult with energy and green building programs for guidance on designing and building more robust wall and roof systems that will last longer and deliver greater ROI. The Home Energy Rating System (HERS), Passive House standards, the building science community, and high-performance-minded manufacturers can help provide details, guidance, and products based on the best building practices that exceed the minimum code standards.
Benjamin Obdyke also can assist in this process. Our product systems not only elevate the performance of the wall system, they also make ordering and installation easier because they are designed to work together.
While housewrap is required by code, it’s important to design above and beyond bare minimums to build longer-lasting, more efficient homes and set your company apart for quality.
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