The detrimental effects of UV on barriers

by nithya_caleb | January 16, 2020 3:45 am

by Peter Barrett

[1]

In any construction project, it takes a combination of the right products and skills to achieve a high-performing building system. In the case of the building envelope, water-resistive barriers (WRBs) play a vital role in the performance of the wall system. Unfortunately, many building professionals may not realize the effectiveness of the barriers can be undermined even before they clad the exterior walls.

The concern is ultraviolet (UV) exposure. Experiential and anecdotal evidence of spun-bond polymeric (polypropylene) WRB membranes deteriorating in the sun after being left exposed for extended time periods prompted an investigation into the effects of UV effects the membrane.

Independent, accredited research commissioned by the author’s company, a manufacturer of air and moisture barriers, has shown when polypropylene WRB membranes are left exposed for as long as it is considered allowable (typically 180 days), it can lose as much as 90 per cent of its original water-penetration resistance. This loss not only has an impact on the effectiveness of the WRB, but also on the performance of the entire wall system because without effective protection, integral structural components are exposed to excessive moisture. This exposure causes all layers of the wall system to degrade, thereby leading to costly repairs.

Understanding and minimizing the impact of UV on WRB is critical to ensure the integrity of the wall system and building performance for many years.

The impact of a failing WRB

[2]

As a key component of the perfect wall, part of a WRB’s role is to protect sheathing from liquid water while allowing moisture to escape from inside wall cavities, and, when installed as part of an air barrier system, the WRB will also resist air movement both out of and into the building. Whether designing the wall or building or paying for it, professionals expect it to be fully functional for the lifetime of the building, maybe 50 years or more. This means each component of the wall, especially the WRB, needs to work and deliver on these expectations.

When any part of a wall system is compromised, it can have adverse effects on the performance of a building. Damaged or under-performing WRBs can cause costly failures and long-term inefficiencies, including:

• damage to insulation, wood, and other structural components due to moisture infiltration;
• mould and air quality concerns from wet wall systems;
• increased energy costs and discomfort for building occupants; and
• potential damage to relationships, reputation, and bottom line brought on by expensive repairs or warranty issues.

To put it into perspective, if the aging process of any WRB is accelerated due to excessive UV exposure, the product may only perform as expected for a few years.

How UV breakdown occurs

[3]

WRBs can get damaged; it is a fact of construction. Most physical damage happening to barriers prior to or during installation can be seen. Holes, cracks, and tears can have a significant impact on a WRB’s effectiveness. These are usually caught and repaired onsite because they are visible. Unfortunately, this is not the case with UV damage. This impact happens at the molecular level, leaving building professionals unaware of and unprepared to deal with the problem.

UV exposure occurs from the time of installation until the WRB is covered with the exterior insulation or cladding. During this period, UV radiation causes the WRB to oxidize, age, and deteriorate. The rate and amount of damage at a molecular level are determined by many factors, including additives such as:

• colour pigments;
• antioxidants;
• UV stabilizers; and
• flame retardants.

How the WRB is manufactured will also have an impact on the degree of breakdown. For instance, manufacturing processes including thermal or shear stresses can initiate early degradation of the WRB. The material experiences heat from the friction that is part of the production process. Higher temperatures cause the polymer molecular chain to break down and react with one another to change the properties of the polymer.

This became common knowledge in the science community as early as 1899 when a Swedish chemist performed experiments that correlated chemical reaction rate constants with temperature. From this research, the Arrhenius Equation theory indicates a 10 C (18 F) rise in temperature will reduce the lifespan by half. Oxidation also has a significant impact on the aging and breakdown of WRBs, which can occur as a result of exposure to heat, certain chemicals, or UV light.¹ This means over-ambitious production methods leading to excessive heat and stress can kick off the degradation process well before the material lands on a jobsite. For polymers, more heat equals rapid aging. So, while a WRB may not physically break down during the allowed exposure time, it is important to understand what happens to the product once it is no longer visible.

Uncovering the unseen damage

[4]

To better understand what happens behind closed walls, an Sageos (a division of the CTT Group) carried out a series of third-party, accelerated aging tests on vapour permeable, self-adhered WRBs.² The research spanned eight months from April to November 2013.

Standard UV exposure tests (such as those required by the International Code Council [ICC] Acceptance Criteria [AC] 38, Water-resistive Barriers, or the Underwriters Laboratories of Canada [CAN/ULC] S741, Standard for Air Barrier Materials—Specifications) use the WRB product samples and expose them to light from UV sun lamps for 10 hours per day for a total of 21 days. In theory, these tests are designed to mimic the conditions naturally occurring in a construction site. These relatively short-term tests do not represent a typical exposure time for WRBs, as some are exposed for nearly 180 days.

As part of the research study, new samples were tested for strength, elongation, and water resistance before being exposed to the UV light to establish a baseline. Those specific tests were chosen to represent the two key, long-term performance criteria one would expect from a membrane in a wall system:

• resistance to water penetration (Hydrostatic Head Tester per the American Association of Textile Chemists and Colorists [AATC] 127-2008, Water Resistance: Hydrostatic Pressure Test); and
• durability (ASTM D5035-11, Standard Test Method for Breaking Force and Elongation of Textile Fabrics [Strip Method]).

The samples were retested after 500 hours of UV exposure and again after 1000 hours of UV exposure, using Cycle 3 of ASTM G155, Standard Practice for Operating Xenon Arc Light Apparatus for Exposure of Non-Metallic Materials.

[5]

It is important to note natural UV exposure varies widely according to geographic location, site conditions, and weather. The 500- and 1000-hour intervals were chosen for all samples to provide consistent and equal exposure for accurate comparison.

Totally, five common self-adhering WRBs were tested, with the acceptable or ‘pass’ criteria set at a minimum of 75 per cent retention of original (‘as new’) test results. All saw a reduction in performance with respect to strength, elongation, and water resistance. The strength of some barriers declined by 80 per cent after being fully exposed for 1000 hours. Even at 500 hours, two of the five WRBs experienced a reduction in strength of 40 per cent or more.

Elongation results and measures of durability were also seen to decline for most products after the full 1000-hour exposure, with four of the five experiencing a reduction of more than 50 per cent. The most significant results, however, came from testing the water resistance of the WRBs. Two products saw a 90 per cent decline in water resistance after just 500 hours of exposure and continued to decline during the remaining exposure hours.

Overall, test results made it clear WRB damage does occur from extended UV exposure during installation periods and the effects can be severe. All WRBs would perform better with less exposure to UV radiation on the jobsite. The sooner the WRB is covered after installation, the less degradation and aging can be expected, and the better its long-term performance within the building envelope. With the right planning and approach, steps can be taken to get ahead of the problem and minimize the impact.

Getting ahead of UV damage

[6]

Many building professionals instinctively turn to manufacturer data sheets for the information they need to select products. In the case of long-term UV exposure, there is no ASTM standard on which manufacturers may base their claim of acceptable jobsite exposure times. However, if this recent UV research has proven anything, it is that more needs to be done outside of this effort to find a solution that best suits the needs of the project. Below are some simple steps to consider when selecting a product.

Know the UV radiation expectations at the site

Understanding the UV radiation expectations at the site can help building professionals plan appropriately for optimal product selection and time demands for exterior cladding installation. For instance, Figure 1 illustrates the UV index for North America in July.

Minimize exposure of WRB to UV

It is advisable to include specifications and schedule details to install the exterior insulation or cladding as soon as possible after the installation of the WRB. By minimizing exposure, one can limit the impact UV will have on long-term performance.

Revisit the impact of failed WRBs used in the past

If building professionals experienced the negative effects of a failed WRB in past projects, it is best to remember the exposure time on that site.

Ask the manufacturer for more information

Reaching out to the WRB manufacturer for more information will come in handy. They should provide information on how the product is manufactured, and some may have data specific to the long-term performance of the material, as well as recommend UV exposure times. Others, however, may not have any test results. It is important to remember a manufacturer’s representative cannot detect molecular damage through a visual check.

Conclusion

Deciding on the best WRB for a project should rely on more than the information provided in manufacturers’ marketing materials. Understanding specific project challenges, exposure rates, schedule demands, and WRB needs will ultimately help one give better results, extend the life of the building, and provide the best performance.

[7]Peter Barrett is the product and marketing manager for Dörken Systems. He has been with the company for more than 12 years. However, his involvement with the design community and building materials industry spans over 25 years. Barrett holds a BA (Hons.) from Queen’s University, Kingston, Ont., and an MBA from Wilfrid Laurier University, Waterloo, Ont. Barrett is a board member of the Air Barrier Association of America (ABAA). He can be reached at pbarrett@dorken.com[8].

Source URL: https://www.constructioncanada.net/the-detrimental-effects-of-uv-on-barriers/

---