June 22, 2009

Building Envelope

Building Envelope Commissioning boosts performance

PETER KENTER

correspondent

By the time a major building project is completed, dozens of trades and sub-contractors have contributed to it.

Building envelope specialists are concerned that conscientious individual efforts may not create a building envelope that functions according to its design.

“So many trades have been involved in the construction of the building envelope over such a long period of time that there’s no guarantee that the building envelope is meeting its original performance requirements or design intent,” said Scott Armstrong, Manager of Sustainable Design Services with the Toronto offices of Halcrow Yolles.

“There’s a big difference between the perspective of a single contractor and a building envelope specialist.”

Armstrong said that the process of building envelope commissioning can help to co-ordinate the work of designers, engineers and trades to ensure the building envelope performs according to specs.

By working together to an accepted quality assurance standard, the complexities of unexpected conditions or unforeseen circumstances during construction have a greater likelihood of being addressed, he said.

“I think that even some of the people who are used to the idea of building commissioning take it for granted that this includes the building envelope,” he said.

“They reason that the building materials being used are common and that the building systems aren’t very complex. That isn’t close to the truth.”

The desired level of building envelope commissioning can be set by the design team, based on the owner’s tolerance to risk, the building type, project complexity, building size, and the desired level of quality.

“The intent to commission the building envelope must be conveyed to the design team as early in the game as possible,” said Armstrong. “And, the framework for commissioning during project design and construction should be agreed on before the project starts, to minimize cost and maximize benefits.”

Armstrong said that ASHRAE Guideline 0 outlines the general process of commissioning, setting the framework by which to address all areas and components of a building.

The National Institute of Building Sciences Guideline 3 builds on that framework by providing specific direction on commissioning the building envelope during each project phase.

Attempts have also been made by the Canada Green Building Council (CaGBC) to apply building envelope commissioning principles to the green building industry by the introduction of a Durable Building credit—MRc8—in the LEED Canada-NC rating system.

“This credit formalizes the material selection process utilizing CSA-S478, Guideline on Durability in Buildings, and requires the development of a Building Durability Plan and an appropriate review process,” said Armstrong. “The CaGBC also includes a fairly good list of credentials that should be required of people or firms that claim to be capable of commissioning the building envelope.”

Green building projects may have the most to gain from effective building envelope commissioning precisely because they often incorporate novel or complex features such as innovative cladding technologies and materials and because of the heightened interaction between the envelope and HVAC systems.

“If members of the project design, construction team or the various trades are unfamiliar with these materials, or if there’s been insufficient review of performance characteristics during design, it can contribute to building envelope failures,” he said.

“If the building envelope fails, it can result in reduced occupant comfort, unrealized energy savings, and premature deterioration of building envelope components.

Trying to re-establish the original performance parameters after the fact can be a costly process.”

The Philip Merrill Environmental Center, the first project in the U.S. to achieve the Platinum rating under the U.S. Green Building Council’s LEED program was considered a successful design.

However, the location and exposure of the building to the Atlantic Ocean, the choice of materials and the way in which they were used to complete the building envelope resulted in long-term repair and maintenance challenges for the building’s owner.

A review of envelope materials and transition details identified several problem areas that could have been addressed by an envelope commissioning agent during design and construction.

“Engage an independent or third-party building envelope consultant early in the project to assist in identifying the materials that will work in that service environment, as well as to identify how materials interface with each other,” said Armstrong.

“Building projects will become increasingly complex, and involve more and more specialty trades, but envelope commissioning can help these complex projects become better buildings.”

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