Finally – the Fog and Myst(ery) surrounding Rainscreen

http://pipes.yahoo.com/pipes/pipe.run?_id=f798f0a8d9468e070178222cfbc78596&_render=rss

well, at least there are now valid and objective means to define the Rainscreen types and their respective performance levels.

Most of the national and regional MCM fabricators and installers have been responding to the growing interest in the “Rainscreen” design concept. In fact, it should be termed and understood for what it is … The Rainscreen Principle. Knowing the proper classification and name of the principle does not however automatically bestow practical understanding. It is because of this ‘misunderstanding’ that the industry ‘fog’ has existed for some time now.
Although the ‘concept’ has been in use in one form or another in the building industry for centuries now (likely dating back to the 1600’s or earlier in Norway with the shingle-lap siding for housing and agricultural structures known as the ‘open-jointed barn technique’), its formalization and value-recognition took root initially in Europe in the early 1900’s, then expanded into Great Britain and Canada where pressure-equalization studies took on a new interest.
It seems, though, that a ‘fuzzy line’ still existed between what had evolved as two distinctly different performance criteria for rainscreen cladding systems – be they wood, metal or masonry. Despite the efforts of many highly recognized research authors and organizations such as Birkeland (Norway), G.K. Garden (Canada) and the NRC-CNRC Institute for Research in Construction (Canada), the principle distinctions within the ‘Rainscreen Principle’ cladding family remained misunderstood by the domestic design and building industry as a whole. To be specific, not many in the industry truly understood what differentiated a ‘Drained and Back-Ventilated (D/BV)’ rainscreen from a ‘Pressure Equalized (PERS)’ rainscreen and what performance differences should be expected. Finally, in 1988 J.M. Anderson and J.R. Gill, CIRCA (Construction Industry Research and Information Association), London, England published what has become the industry definitive treatise on rainscreen entitled Rainscreen Cladding a Guide to Design Principles and Practice.
This ‘fuzzy line’ misunderstanding has led to numerous specifications blending the two design principles and suppliers of systems either knowingly or unknowingly laying claim to performance levels of one type, when in fact their system was truly the other. All the while, the critical weather resistant surface of the building envelope received little attention in specification or detail … the air/water barrier (or weather resistant membrane or coating) seemed a secondary thought or concern. According to the abaa (Air Barrier Association of America … www.airbarrier.org) this critical weather-proofing element should receive as much attention as the aesthetic building envelope system, if not more!
In an attempt to try to clear up this lack of understanding before injury to the industry took hold, the Metal Construction Association (MCA), Chicago, IL appointed a Rainscreen Task Force in January 2005 as a research and educational group attached to its Wall Panel Council. The result of this effort to educate the industry culminated in February 2007 with this issue of the Task Force’s white paper entitled Understanding ‘The Rainscreen Principle’, dated December 14, 2006. This paper presents background, conventional wall design summaries, and fundamental performance criteria, but most importantly, delves into the fundamental differences between ‘Drained/Back-Ventilated (D/BV)’ and ‘Pressure-Equalized/Compartmented (PER)’ rainscreen systems. These two approaches to controlling weather penetration of the building envelope exist equally underneath The Rainscreen Principle banner; however they are distinct and different in their performance and design principles. Accordingly, they should not be blended, nor should they be confused as to their respective levels of expected performance. Just because a cladding system is a ‘Rainscreen’ does not automatically mean it is pressure-equalized! I would urge all readers of this blog to go to the Metal Construction Association’s website at www.metalconstruction.org and download this white paper. It should be the beginning of a clearer understanding and eradication of the ‘fuzzy line.’
In order to further publicize the rainscreen issues and concerns, MCA’s Rainscreen Task Force presented a seminar at the 2007 METALCON International (www.metalcon.com) show in Las Vegas on October 3rd entitled Effective Design & Installation of Rainscreen Cladding. This seminar presented the history of ‘The Rainscreen Principle’, differences between the ‘D/BV’ and ‘PERS’ rainscreen types, a review of general design types, technical design and performance elements which distinguish the two types, and finally the ongoing AAMA testing programs and protocols being developed for both types.
It was this last subject matter (the testing programs by AAMA) that truly held-out a glimmer of real hope for the industry. Up until this point in time, while numerous technical documents and papers had been issued describing scientific analysis and laboratory testing results supporting the theories for both ‘D/BV’ and “PERS’ (the latter receiving much more attention as the fine line of pressure equalization is not easily achieved), no industry-wide definitive test protocol had been developed or adopted by any recognized industry organization. Not until now anyway!
GOOD NEWS!!
The American Architectural Manufacturers Association (AAMA) has stepped up to provide the sorely needed testing protocols that will, in large part, take the guesswork out of whether or not various systems truly perform under the banners of ‘Pressure Equalized’ or ‘Drained/Back-Ventilated’ rainscreens. AAMA has now concluded two separate Task Group Studies resulting in specific and distinctive testing and classification methods for both ‘Pressure Equalized’ and ‘Drained and Back-Ventilated’ rainscreen cladding systems.
Pressure Equalized Rainscreen (PERS) – After a little over two years of meetings and data collection as a result of various testing methods development, the AAMA Pressure Equalized Rainscreen Task Group submitted for and gained approval from AAMA’s Methods of Test Task Group in December 2005 AAMA 508-05 Voluntary Test Method and Specification for Pressure Equalized Rain Screen Wall Cladding Systems. Subsequently, this test procedure was updated, revised and re-issued as AAMA 508-07 Voluntary Test Method and Specification for Pressure Equalized Rain Screen Wall Cladding Systems in May 2007. This testing procedure and protocol is available for a nominal fee at AAMA’s website www.aamanet.org ; click on Publications Store.
Drained and Back-Ventilated Rainscreen (D/BV) – Beginning toward the end of 2007, the Drained and Back Ventilated Rain Screen Wall Cladding Systems Study Group (D&BV Study Group) began work under the auspices of AAMA and hosted by Architectural Testing, Inc., York, PA. On July 31, 2009 the Study Group concluded its testing and technical meetings by addressing all balloted comments and concerns. The final proposed draft of Voluntary Test and Classification Method for Drained and Back Ventilated Rain Screen Wall Cladding Systems was transmitted to the Chairman of the AAMA Methods of Test Task Group on August 17, 2009 for formal approval, processing and publication. The proposed testing and classification method of test was approved during the AAMA National Fall Conference in September 2009 and subsequently was assigned formal test method number AAMA 509-09, and released for publication in October 2009. This formal document is now available publically through AAMA’s website ‘Publications Store’.
Let’s all work to assure that these definitive testing methods become the standard for evaluating performance of proposed systems so that conjecture, supposition and subjective claims become a means of the past and our road to clearly understood and expected performance criteria creates a solid foundation for the entire industry.
Your comments are welcome!