Insights from Dr. Joe Lstiburek: Ultraviolet Damage

Your building materials could be getting sunburned this summer, but it’s not visible to the naked eye. And, over time, this unseen damage will continue to get worse.

The problem begins when WRBs are left exposed during installation. When this happens, they can lose as much as 90 percent of their original water penetration resistance over time, depending on the brand. This is a significant loss that has an impact not only on the effectiveness of the WRB, but on the long-term performance of the entire wall system as well.

Unlike holes, cracks, or tears in a WRB, damage from UV light happens at the molecular level, so it may not appear until well after the exposure has happened and often when the wall is completely enclosed.  Ongoing oxidation and heat degradation will continue the process. As a result, a building can be performing poorly without any immediate visual evidence of the cause, leaving building professionals unaware and unprepared to deal with the problem.


Six Facts About UV Light

  1. UV rays are strongest between 10 a.m. and 4 p.m.
  2. UV rays are stronger during spring and summer months. This is less of a factor near the equator where UV rays are consistently strong all year.
  3. UV exposure goes down as you get farther from the equator.
  4. Higher elevations have higher UV ray intensity.
  5. The effect of clouds can vary, but UV rays can get through even on a cloudy day.
  6. UV rays can bounce off surfaces like water, sand, snow, pavement, or even grass, leading to an increase in UV exposure and intensity.


Using best practices for scheduling, planning, and covering your WRB as soon as possible is always highly recommended. It is a matter of how much of the material’s life do you want to consume while exposed during the construction period and how much do you want to save for the service life of the building. By minimizing exposure, no matter the product, you will help to limit the impact UV will have on the long-term performance of your WRBs, and ultimately your building.

Dr. Joe Lstiburek, acclaimed educator and founding principle of Building Science Corporation, recently sat down with Dörken to break down the complexity of UV light and how long building materials should be left exposed. Although one of three principle damage functions, we often don’t consider the significance of UV damage in our building systems and building assemblies the same way we do heat and water. With this in mind, Lstiburek explains how to select the right products to ensure they perform during the useful service life of the building.


Dr. Lstiburek holds a Bachelor of Applied Science in Mechanical Engineering, a Master of Engineering in Civil Engineering, and a Doctor of Philosophy (Ph.D.) in Building Science. Get the full scope of Dr. Lstiburek’s work, accolades, and contributions to the industry over at Building Science Corporation.


The Best Defense

Dr. Lstiburek knows that product selection is crucial. Once a WRB is enclosed behind the wall, it’s difficult and expensive to assess its condition and performance. Whether you’re the architect, owner, or a contractor, you need to know the facts when choosing a WRB for a project. Standing up to prolonged UV exposure on the jobsite, Dörken’s new DELTA®-STRATUS SA is the only WRB with a fourth layer of UV protection.

DELTA®-STRATUS SA is engineered with two outer layers, made up of high-strength, spun-bonded polypropylene fabric, which are thermally bonded to a highly vapor permeable, watertight polymeric middle layer. On top of all of this, the new product features an innovative acrylic UV-resistant coating that is proven to provide true UV protection currently unheard of in the building industry. This level of extreme protection means that DELTA®-STRATUS SA will be able to provide the high-performance weather protection builders need to ensure the long-term integrity of their buildings.

To learn more about the long-term damage of UV exposure on building materials, read DELTA® Insights.