27 May 2009

Pressure Equalized Rainscreen Literature

Updated 11 October 2008

Here is some of the best succinct literature on Pressure Equalized Rainscreen (PER). I have provided short descriptions to help you choose which you want to read if you don’t have time for or interest in all of them. My recommendations are Number 4 for the design professional and Number 7 for the manufacturer.

1. “Rain Penetration and its Control” by G. K. Garden, 1963, http://irc.nrc-cnrc.gc.ca/pubs/cbd/cbd040_e.html, was the first publication on our continent regarding rain screen walls. The principles he espoused have been confirmed by laboratory and field testing over the ensuing years, but it’s only recently that the industry has begun to develop a performance-based definition for pressure equalization.

2. “Brick Masonry Rain Screen Walls”, BIA Technical Notes 27, 1994, http://www.gobrick.com/BIA/technotes/t27.htm, applies PER principles to brick masonry construction. Although the recommendations provided do not meet the prescriptive requirements for PER discussed below, there has been some field testing that seems to confirm that it works.

3. “Infinity System Specifications – A Patented Pressure-Equalized Rainscreen Exterior Insulation and Finish System”, Dryvit, 1994, http://www.dryvit.com/fileshare/doc/us/specification/ds136.pdf, is a PER EIFS specification. The significant value of it is that it includes a performance requirement for PER what was developed for them by the laboratory in Canada that has been instrumental in a lot of the Canadian PER research. The significant drawback is that its performance requirement is a vague "in accordance with procedures developed by the National Research Council of Canada, Institute for Research in Construction."

4. “The Design of pressure-equalized rainscreen walls,” Poirier, Brown, and Rousseau, 1995, http://irc.nrc-cnrc.gc.ca/pubs/fulltext/prac/nrcc48643/nrcc48643.pdf, gives an excellent overview of the topic and basic prescriptive requirements, such as number and size of openings, to create a PER. If you can only read one of these articles, this would be the one I recommend.
   *Unfortunately it seems to have recently disappeared from the web. An adequate replacement document is "Construction Technology Update No. 17: Pressure Equalization in Rainscreen Wall Systems," Roussau, Poirier, and Brown, 1998, http://www.nrc-cnrc.gc.ca/eng/ibp/irc/ctus/ctus-n17.html.

5. “The Rain Screen Principle and Pressure-Equalized Wall Design,” AAMA CW-RS-1-04, available from AAMA, is essentially an adaptation of Garden to the curtainwall industry. It is heavy on theory and light on both prescriptive and performance requirements.

6. “Protection from Precipitation Ingress through Walls – Parameters and Criteria for Invoking Mandatory Open-Rainscreen,” Chown, 2001, http://irc.nrc-cnrc.gc.ca/pubs/fulltext/nrcc46002/nrcc46002.pdf, recommends that PER be used on all non-temporary, non-masonry commercial construction. Note that this is a committee paper and, as far as I know, has not been adopted or promoted by NRC. Never-the-less, because it is an argument for a change to the Canadian Building Code, it offers insight on the benefits of various rainscreen technologies.

7. “Voluntary Test Method and Specification for Pressure Equalized Rain Screen Wall Cladding Systems,” AAMA 508-07, available from AAMA, was recently developed by the metal panel industry and is growing in acceptance and use by the manufacturers. It is the only widely available prescriptive definition of PER that I am aware of, and seems to have applicability beyond the metal panel industry. For example, Centria has tested the horizontal joints of their Formawall to this standard. (The horizontals are PE, but not the verticals.) In my conversations with exterior enclosure manufactures and their reps, I challenge them to investigate this test, and I am seeking out those who have already done so.

One of the beauties of PER is that even if the system is imperfect (due to an installation defect), the system will still be successful in keeping water out of the building. However, as in any wall, water may become entrained within the system due to defects in materials and workmanship, so it is still important to provide either drainage or drying capability, or both. AAMA is working on performance-based tests to quantify these as well. In the meantime, we have the following literature:

8. “Designing Exterior Walls According to the Rainscreen Principle,” Brown, Chown, Poirier, and Rousseau, 1999, http://irc.nrc-cnrc.gc.ca/pubs/ctus/ctu34e.pdf gives an overview of the need.

9. “Understanding ‘The Rainscreen Principle’”, Metal Construction Association (MOA), 2006, http://www.metalconstruction.org/pubs/pdf/mca07_Rainscreen.pdf, gives an overview and comparison of Drained/Back-ventilated and Pressure Equalized rainscreen systems.

10. “Evaluation Guideline for a Moisture Drainage System Used with Exterior Wall Veneers,” ICC EG356, 2006, http://www.icc-es.org/criteria/pdf_files/eg356.pdf, includes a rudimentary drainage test that could be used to establish alternative compliance requirements from a code point of view. Read it in conjunction with Chapter 14 of the IBC, which requires drainage in all non-masonry walls unless they have been tested to ASTM E331 for 2 hours (i.e., are a tested barrier wall).

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