The Damaging Effects of UV Exposure on Air- and Water-Resistive Membranes


In many commercial construction projects, the ordinary practice is to protect the work site by installing air- and water-resistive barriers (WRBs) early.

But this practice does not account for the damaging effects of ultraviolet (UV) rays on the air and moisture membranes that are left exposed during construction.

Misalignment between product data sheets and real-life performance

What many manufacturers’ data sheets fail to make clear are the consequences of exposure to UV light on the performance of WRBs.

Unfortunately, the results can be significant. Testing data shows that leaving products exposed for as long as considered allowable by some manufacturers can result in as much as 90% loss of the original water resistance of the product, as reported on the manufacturers’ data sheets.

That’s a major loss that can have an enormous effect on the performance of the building and can call to account the decisions of Architects and Contractors.

The problem with manufacturers’ warranties and claims

The data sheets that accompany products like WRBs are vital documents for product evaluation, installation instructions, and understanding the performance expectations and warranties. Designers, Contractors, and Building Owners rely on these data sheets and their own personal experience to make decisions about crucial products like WRBs.

A significant downfall of most WRB data sheets, however, is that they fail to provide two vital pieces of information about the impact of UV exposure on the long-term performance of their product.

Without this information, it becomes difficult to choose the best WRB for a project.

  1. UV exposure times are provided without explaining the long-term impact on performance and durability of the product.

While a WRB may not physically break down during the allowed exposure time, it’s important to understand what happens to the product once it is covered by cladding. Often the UV exposure recommendations (some as long as 180 days) are marketing claims and are made based on the short-term performance of the product and user convenience, rather than any testing results or research.

In fact, the industry lacks any American Society for Testing and Materials (ASTM) standard testing requirements to identify acceptable exposure limits. Without this information, manufacturers are failing to provide users with the data needed to understand the product’s long-term performance.

  1. Most products indicate a single UV exposure limit without any clarification on the impact of the location or season.

Manufacturers’ recommendations generally include a single acceptable time exposure for their product or a general time range. These recommendations don’t include considerations for seasonal fluctuations or geographical differences.

Winters in Ontario would expect to see significantly less exposure than summers in Florida, so 6 months in both locations should not be considered equal.

Issues with a damaged WRB/air barrier

A less-than-perfect building envelope can have an enormous effect on the performance of a building.

Damaged and underperforming WRBs cause costly failures and long-term inefficiency of the building, including:

  • Damage to insulation, wood, and other structural components due to moisture infiltration;
  • Mold and air quality concerns from wet wall systems; and
  • Increased energy costs and discomfort for building occupants due to air leaks.

Architects and Contractors also should consider the impact of a poorly performing building on their business. Buildings that don’t perform up to standards only a few years after construction can not only affect their reputation, but also bring costly investigations, repairs, replacements, warranty claims, and litigation.

The hidden impact of UV damage

Damage to a building’s exterior finish, or holes, cracks, or tears in the WRB prior to it being enclosed, can be seen and repaired.

Damage to WRBs from UV light, however, may not appear until well after the exposure has happened, and often when the wall is completely enclosed.

As a result, a building can be performing poorly without any immediate visual evidence of the cause.

Because UV exposure occurs from the time of installation until the WRB is covered with the exterior insulation or cladding, UV radiation causes it to start to age and deteriorate almost immediately. If this process is accelerated, the product can begin to underperform within a few years, despite the fact that an Architect, Contractor, or Owner might have the expectation that a WRB will perform for the life of the building (50 years or more).

You might also like…Dr. Joe Lstiburek Explains UV Damage

How UV breakdown occurs

When WRBs age and break down due to UV exposure, the damage occurs at the molecular level. The rate and amount of the damage of any individual brand of WRB is determined by many factors, including additives like color pigments, antioxidants, UV stabilizers, flame retardants, and others.

How the WRB is manufactured can also have an impact on the degree of breakdown. Manufacturing processes with excessive thermal or shear stresses can initiate the degradation of the WRB.

Research shows that oxidation has a significant impact on aging and breakdown of WRBs, which can occur as a result of exposure to heat, certain chemicals, or UV light. Manufacturers combat some of this vulnerability through the addition of antioxidants and UV stabilizers in their products. Regardless of the WRB product, however, all will experience aging when exposed to UV radiation, humidity, freeze and thaw cycles, and extreme cold or hot temperatures.

How to choose the best air- and water-resistive barrier for your project

Whether you’re the Designer of a building, a Contractor, or the Owner, you want to have all the information at hand when you choose a WRB for a project.

WRBs play an important role in the long-term function of the building, and you’ll need to have the right UV-resistant water barrier and installation process in order to achieve the perfect wall.


Beware of UV

It’s important to understand that UV exposure will impact the performance of the WRB you install. There are many different factors that influence how much that exposure will impact long-term results, but all the WRBs tested eventually experienced negative results.

Understand your environment


The graphic above shows the UV index for the United States as of May 2022. If you understand the UV radiation expectations at your site, you can consider your product and exterior cladding installation appropriately.

Minimize exposure

Include specifications and schedule details to install the exterior cladding as soon as possible after the installation of the WRB.

By minimizing exposure, the potential damage UV will have on long-term performance is limited. If the Owner or the Architect is concerned that the Contractor prefers to have more flexibility in their schedule, it will be important to communicate the consequences only a few weeks can have on long-term performance.

Ask the manufacturer for more information

If you have a preferred product that you have worked with in the past, you should reach out to the manufacturer and ask them for more information. Some may have data specific to the long-term performance of their product given the UV exposure recommendations they provide. Others, however, may not have any test results.

Check your own records

If you’ve been in this business for several years, you may have experienced the impacts of failed WRBs in buildings you’ve been involved in. Ask yourself which product you used in those cases, and how long you tend to leave the WRBs exposed before covering them. It’s also an option to ask other professionals in your area about their experiences with a specific product or process.


If you’re looking for a UV-resistant air barrier for your projects, DELTA®-STRATUS SA is the only vapor permeable air- and water-resistive barrier with a fourth layer of added UV protection. DELTA®-STRATUS SA was tested using real-world conditions to ensure it retains optimum water-penetration resistance, air tightness and building integrity.