High-Performance Facades: Performance Attributes – What to Consider & Measure

Mic Patterson (President & Director of Strategic Development for Enclos) and Jennie Matusova (Zaha Hadid Architects)

Article originally published 7 March 2013 at enclos.com

While Extended Industry Standard Architecture (EISA) develops a set of attributes for high performance and green high performance, qualitative terms like “integrates, optimizes and outperforms” are subjective and relative measures that yield no concise metrics for evaluation. The National Institute of Building Sciences (NIBS) is one of the organizations working to define these needed metrics, baselines, benchmarks and verification strategies, specifically with respect to the building envelope. The building envelope is the nexus of many, often conflicting, functional demands, or as NIBS states: “many high-performance attributes interact at the envelope” (National Institute of Building Sciences n.d., 4). NIBS has leveraged EISA 2007 to define a set of performance attributes relevant to the building envelope, with an emphasis on enhanced security. The following attributes are similarly derived.

Attributes for Determining Performance of the Building Facade

Building energy performance is significantly impacted by various attributes of the facade. The building skin provides thermal insulation, mitigates air infiltration and controls solar energy radiation, providing daylighting opportunities to reduce electricity consumption and heating loads resulting from artificial lighting. Solar energy harvesting technologies will one day contribute to net-zero and net-plus energy buildings. Natural ventilation through the facade can play a significant role in building energy efficiency.

Environmental impacts of the building facade include energy consumption and resulting emissions over the operations phase of the building lifecycle, as well as larger, more lasting impacts. The lifecycle context requires that embodied energy, disassembly and end-of-life impacts also be considered. Waste generation through the building lifecycle is another important consideration.

Safety and security are provided to the building occupant by the facade systems (at the most fundamental level, keeping bugs and burglars out, and babies in). Protection from weather extremes includes impact resistant design practices. Blast loading criteria is now commonplace in facade design. NIBS references ballistic, chemical, biological and radiological protection.

Durability is an often neglected but fundamental aspect of performance and sustainability for all building systems, with special significance for the facade in its protective role of separating inside from out. In the majority of cases, a predicted service life for a building and its facade system goes undefined. Most damage and deterioration in a building can be traced to moisture penetration and migration through the building skin. Weathering is a particular concern for the exposed elements of the facade. Renovation requirements should be anticipated and planned for over the full building lifespan.

Cost-benefit, or economic efficiency, is yet another important performance consideration, which takes into account at what cost performance attributes are being amplified, verses the benefit the improvement provides. High performance and green programs are often motivated by promotional and image interests (greenwashing) and may ignore simpler and less costly solutions capable of providing equal or greater benefit at less cost, solely because they do not provide a high-profile green “wow” factor.

Human comforthealth, and productivity are profoundly affected by the facade system. The facade provides thermal and acoustical comfort, daylight, visual comfort and glare control, as well as connection to the natural environment. Natural ventilation through the facade can greatly enhance indoor air quality. Favorable biophilic facade attributes are well documented in providing a more productive and healthier indoor environment (Terrapin 2012). Even small improvements in productivity can quickly trivialize related first costs.

Sustainability criteria are included by the EISA in evaluation of high-performance systems. This opens the evaluation to the wide and varied considerations – and the inexact science – of sustainability. Many of the issues discussed here are fundamental sustainability issues. These considerations also include emergent issues like resilience, or the ability of a system to withstand extreme and unanticipated future conditions. Sustainability considerations will drive future development of facade technology. Water harvesting, for example, will become an increasingly important function of the facade in many geographic areas as supplies of potable water diminish. Lifecycle Assessment (LCA) will become the framework for the sustainability metrics that will drive future development of facade technology.

Operational considerations for the building facade include its integration with other building systems, the user interface, and maintenance and renovation requirements over the operational phase of the building lifecycle. Provisions must be considered to keep a building operational during planned renovation cycles, including disruptions to fuel and water supply, extreme weather conditions, and political instability.

Using the EISA definition then, a high-performance facade would be one that integrates and optimizes the above attributes on a lifecycle basis. A high-performance green facade is a high-performance facade that outperforms similar buildings with respect to key sustainability metrics as described above, again, on a lifecycle basis. Context, however, will determine the attribute set and the priority of those attributes as represented by the project specific criteria adopted for each attribute.

The EISA definition effectively leaves no performance attribute off the table when it comes to evaluating high-performance systems. But is it reasonable to “integrate and optimize” all of these attributes in each application? What if a facade application optimizes one area–energy efficiency, for example, but ignores durability analysis or acoustical performance? What about greenwashing? If a facade design employs high-performance materials and technology in an application where near equivalent performance could have been achieved with a simpler and less costly strategy (i.e., an expensive double-skin system where triple-glazed IGUs would have sufficed), is the system still deserving of the high performance designation? One begins to recognize how easily the term high performance may be applied with inadequate discrimination. High performance and green are terms that should be protected from dilution of meaning by clear definition and standards of practice.

While helpful to have some relevant performance attributes identified, related metrics are still lacking. The evaluation of some of these attributes may be inherently subjective, while others lend themselves to quantitative measure. In either case, appropriate evaluation criteria must be developed.

National Institute of Building Sciences n.d. “High Performance Based Design of the Building Envelope.” Accessed 11 February 2013: http://c.ymcdn.com/sites/www.nibs.org/resource/resmgr/HPBC/HPBDE_Workshop-Project_Overv.pdf

Terrapin 2012. The economics of biophilia: Why designing with nature in mind makes financial sense. New York: Terrapin Bright Green, LLC. Accessed 8 June 2012:
http://www.terrapinbrightgreen.com/

© Enclos Corp 2013

This entry was posted in ECO in the City. Bookmark the permalink.