A cement plaster (stucco) project in downtown
Los Angeles over 2 inches of continuous rigid foam.
The new energy code has taken effect in my home state of California. While that may seem to be a world away from most of you, it is closer than you could imagine. The tougher energy laws that affect us with regard to exterior wall systems and claddings are a direct result of the American Society of Heating and Refrigerating and Air-Conditioning Engineers Inc. standard 90.1. This national standard is the model that the national code, as well as states, will adopt as a minimum to build their own energy codes. While this standard covers a wide variety of items for designers, specifiers and energy consultants, it is the building envelope we are primarily concerned with as it has a direct affect on us in the wall and ceiling industry and plastering trades.
Designers have two basic options to be compliant with the new energy code:
The prescriptive method
The performance method
The prescriptive method follows a set of guides or tables set by ASHRAE or the local state energy commission to achieve a preset target number for compliance. For example, the prescriptive method may require an exterior wall on a specific project to be U/R-19. The tables in the ASHRAE standards or state standards will prescribe a parameter to meet this U or R value. With steel framing, it is most likely going to require some additional rigid foam insulation over the steel framing members.
“The Energy Code and Plaster Assemblies: How to
Make Continuous Insulation Work” is available as a free download at www.tsib.org.
The performance method (sometimes called the “trade-off” approach) is to find energy values in other areas of the building that will allow you to build the exterior wall as you have always done in the past. This will most likely require a specialized energy consultant capable to clearly and convincingly demonstrate to the building department that code compliance has been clearly achieved.
On behalf of the Western Conference of Wall and Ceiling Institutes, we felt it important that we be on the lead side of the equation. This was an opportunity to show the design community that we can be the solution to the problem the energy codes have presented them. Since California had adopted the new code, I contacted Michael Logue from the Technical Services Information Bureau and Mark Fowler from the Western Wall and Ceiling Contractors Association to see if they were interested in working together. An enthusiastic “yes” was the response.
As it turned out, Bob Drury, Terry Kastner and Jim Young from the Northwest Wall and Ceiling Bureau were also on board for a joint project. Young felt the timing could not better, as Oregon was in the process of implementing its own strict energy code updates. Locally, Jim Johnson from the Plaster Information Bureau, Bruce Bell from the Sacramento Valley Plaster Bureau and Ben Duterte of the Drywall Info Trust Fund were also contacted and we all began sharing ideas and experiences. The direction became clear: A detailed technical brochure on how cement plaster can be used with the new rigid insulation requirements over steel framing was necessary to deliver the message.
BREAKING NEW GROUND
While some may think that plaster and plaster-like systems or assemblies incorporating rigid foam is breaking new ground, I can assure you we have been doing it successfully for decades. The first and most obvious choice is EIFS. This system was designed specifically for this purpose-energy efficiency. Code approved and time-tested, EIFS is what Europe and North America can count on to meet and exceed even the toughest energy code requirements. However, some owners and designers strongly prefer cement plaster over EIFS. But can cement plaster work with rigid foam? Is it code legal? How about testing?
As it turns out, in discussions with friends and colleagues with decades of experience in plastering, cement plaster and rigid foam has been done for years in markets from San Diego to Seattle and across the country. And when some best design practices are followed, it works out quite well. Bryan Stanley from the TSIB office noted that ASTM C 926, the standard for cement plastering, clearly states that cement plaster may be applied over rigid foam. The mission was clear: visit jobs and find out more about cement plaster over foam.
Mark Fowler, who has a long family history in plastering, noted that his father and uncle applied cement plaster directly over foam in the 1950s as butcher stores and cold storage warehouses needed an insulated wall they could regularly hose down. The plasterers applied shower finish over a basecoat of cement with no lath. Not that we would ever suggest applying cement plaster to foam without a lath but it proved what the Portland Cement Association has published for decades-cement plaster bonds tenuously to most rigid foams.
Bell and Johnson both commented on the bonding ability of cement when used with one-coat stucco systems. While they had concerns about the systems in commercial use, there is precedent and more proof of cement’s ability to bond to foam substrates. Albert Carrillo, of the WWCCA’s Arizona branch, has vast experience in plastering and confirmed cement plaster over foam has been done in Arizona and New Mexico with great success.
A job in Seattle
where cement plaster was applied over 2 inches of rigid foam more
than 10 years ago.
So with a consensus of these experts in plastering and the sum of our knowledge, we produced the brochure “The Energy Code and Plaster Assemblies: How to Make Continuous Insulation Work.” The conference decided on three basic continuous insulated assemblies for cement plaster. A basic simplified specification and very basic details are provided as a guide on our recommended best practices. (The brochure is available as a free download at www.tsib.org.)
The brochure also has an ASHRAE table to guide designers and contractors on how much and what type of rigid insulation will meet the prescriptive requirements of the code. Eventually, we plan to have a series of details on various other CI plaster systems available for designers to use when cement plaster and rigid foam is desired or required.
After all was complete, conference committee members reviewed the brochure and we went to print. Then it dawned on us: Dick Gorman had not reviewed the brochure. Gorman is one of the authors of the Plaster and Drywall Systems Manual first published in the 1960s and is probably the most knowledgeable expert in plastering in North America. How could we forget him? I sent a copy for his review and to our delight, he liked it and was in agreement with our recommendations.
The plaster industry is prepared to meet the new challenges that face us. We may have to do business just a bit differently, but we will survive and hopefully even thrive. We may have to learn new terms like U factor as they replace the older R value system we know and love. But that is the future. We believe the Western Conference Energy Brochure is that bold new direction.
Someday, every new building with stucco may be placed over a solid substrate of foam. We could be leading the way to using significantly lower amounts of energy to heat and cool our homes and offices, and we may make a small profit in the process. Our systems, one-coat stucco, three-coat cement plaster and EIFS can all be part of a revolution to save energy and what is wrong with that? W&C
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