Understanding engineered rainscreens

Industry involvement
Over the last few years, there has been a shift in the building industry toward all-wall drainage and ventilation materials. Organizations, such as the Air Barrier Association of America (ABAA), were one of the first to point out the importance of protecting the entire building envelope by using a system, not component approach. All-wall drainage and ventilation mats should be considered part of that system.

Last July, the Building Enclosure Moisture Management Institute (BEMMI) created the testing criterial that became the standard for ASTM 2925-14, which lays out the guidelines to specifying the correct type of engineered rainscreen drainage mat. The strict criteria include elements such as:

  • heat aging;
  • compression testing;
  • surface burning;
  • drainage efficiency;
  • ultraviolet (UV) testing; and
  • nominal thickness testing.

(It is important to note drainable house wraps are not engineered rainscreen drainage mats—they simply do not meet the requirements of ASTM E2925-14.)

Both stucco and manufactured stone applications are seeing the value of a drained cavity created by these all-wall drainage mats as well. The cavity created by these drainage mats gives a cavity wall concept without the cost of a true cavity wall system. Organizations, such as the Masonry Veneer Manufacturers Associations (MVMA), make reference to drainage mats in the third and fourth editions of the Installation Guide for Adhered Concrete Masonry Veneer. Major siding manufacturers are also putting these drainage mats in their installation instructions and technical details.

Points of consideration for specifying and using all-wall drainage mats include:

  • total rainfall and frequency;
  • wetting and drying cycles;
  • wind and storm conditions;
  • freeze-thaw conditions;
  • temperature; and
  • humidity.

It is recommended to use all-wall drainage mats in geographic locations receiving 508 mm (20 in.) or more of rainfall annually. In Oregon, it is becoming code for areas receiving upward of 1524 mm (60 in.) of rainfall a year to use all-wall drainage mats—such a requirement may also end up occurring in similar regions in Canada down the road.

Areas with high wind content are prime candidates for rainscreen drainage mats. As an example, an 80-km/h (50-mph) wind will exert 41.3 kPa (6 psi) on a wall’s surface—enough pressure to force moisture into cracks of any size.

Conclusion
In summary, building with rainscreen technology allows moisture to drain and ventilate properly by reducing the amount of rainwater allowed to linger in a wall system. Building owners should see a significant decline in efflorescence, staining, structural decay, and poor IAQ, along with an increase in the building’s lifecycle. All-wall drainage mats are cost-effective and have proven to be an effective way to improve the life and performance of a building.

LolleyHeadShotKeith Lolley is a graduate of Southern New Hampshire University with a bachelor’s degree in business management. He has been involved in the construction industry for 16 years and is the vice-president of Advanced Building Products while currently holding a seat on the board of directors for the Building Enclosure Moisture Management Institute (BEMMI). Lolley can be reached at klolley@abp-1.com.

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