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Building Envelope Commissioning

Alan Scott, Posted 05/01/2017

When LEED was first released in 2000, most building owners, developers, and design and construction teams were unfamiliar with commissioning. The Fundamental Commissioning (FCx) prerequisite and Enhanced Commissioning (ECx) credit in LEED introduced a new best practice to many project teams, demonstrating that HVAC and lighting systems benefited from a little extra attention to ensure they were installed and operating as intended to save energy and improve indoor environmental quality.

Commissioning acknowledges that even with the most professional and attentive design, construction and facility management teams, critical details can fall through the gaps left between the various specialists who design, install and operate modern building systems. As with the original, LEED v4 has introduced us to the established, but still uncommon, practice of Building Envelope Commissioning (BECx). While it is not a prerequisite, architects should become familiar with BECx and learn how they, their clients and the general contractor can benefit from the practice.

 

Why is BECx important?

Advances in material technology have helped unleash the creative freedom of architects while also supporting enhanced thermal performance and moisture management in building envelopes. However, these high-tech envelope systems are still composed of multiple components made by different manufacturers and installed by different trades that all must come together to form a cohesive enclosure. Also, as we work toward zero net energy buildings, we are reminded that envelope performance (and the resulting passive effect on heating and cooling loads and thermal comfort) becomes increasingly important.

We are now familiar with the role of the Commissioning Authority (CxA) for FCx and ECx serving as a building system performance facilitator, interfacing with the mechanical, electrical and plumbing (MEP) design engineers, general contractors, MEP subcontractors, and the operators who will inherit the completed building. Similarly, the Building Envelope Commissioning Authority (BECxA) helps guide the design, detailing, installation and maintenance of high-performance building envelope systems.

In both cases, the CxA leads a process to define performance expectations, review the execution in design and construction, validate that the desired performance was achieved, and ensure the building operations team is prepared to maintain that performance over time. Architects are skilled at material selection, specification and detailing. But, sometimes it helps to have an expert on the team to supplement your own knowledge. The BECxA understands design, material properties, building science, and the realities of construction and maintenance.

 

What is BECx?

The BECx process begins as early as pre-design, with the development of the Owner's Project Requirements (OPR), which spells out the owner's expectations for appearance, thermal performance, durability and maintenance for the building shell.

Based on those requirements, the architect will create the Basis of Design (BOD) document that will inform the BECxA in developing a commissioning plan that defines the quality assurance process to verify that all requirements will be met.

During the design phase, the BECxA will review the architect's details and specifications, identifying potential risks and making recommendations to mitigate or eliminate them. One common source of problems is the incompatibility of proposed materials in enclosure systems, such a vapor permeable sheathing combined with a polyethylene vapor barrier that could trap moisture in the wall during hot and humid conditions.

During construction, the BECxA will review submittals, and inspect mock-ups and initial installations to identify potential issues before all installation is complete (and costly corrections are required). They will also develop and witness tests of mock-ups and completed installations to ensure that the systems are functioning as designed.

Testing is performed using infrared cameras, tracer smoke, calibrated water hoses, moisture meters and blower door assemblies. This testing can reveal both design flaws and construction deficiencies, especially in critical areas (like the exterior wall enclosing a negatively pressurized ceiling plenum of a positively pressurized under-floor air delivery system, where the consequences of infiltration or exfiltration are magnified). After construction is complete, the BECxA will ensure that the facility manager or building engineer has all the information on the building enclosure materials and systems and is fully trained on required maintenance.

 

One Size Does Not Fit All

An important role of the BECxA is to understand the unique circumstances of each building project and to propose the best approach to meet the owner's requirements. Some testing procedures can be complicated or costly to execute, depending on the size of building and type of enclosure system. The BECxA must evaluate and inform the owner and architect about potential risks and balance those against the costs of addressing them in the commissioning process.

The Enhanced Commissioning credit in LEED v4 now includes options for monitoring-based commissioning (1 point) and envelope commissioning (2 points). This credit option requires that commissioning process activities be included in the development and execution of the commissioning plan. This must be carried out in accordance with ASHRAE Guideline 0-2005 and the National Institute of Building Sciences (NIBS) Guideline 3-2012, Exterior Enclosure Technical Requirements for the Commissioning Process, considering energy, moisture, indoor environmental quality and durability. These publications are valuable guides to the best practices and procedures necessary to successfully complete a BECx process, regardless of project's LEED aspirations.

The proper construction and maintenance of a high-performance building enclosure ensures that the building will maintain its aesthetic appeal, durability, energy performance and indoor environmental quality while reducing the long-term maintenance and replacement costs. Implementing a building envelope commissioning process can create real value for the building owner and occupants, while helping to protect the architect and general contractor from the costly consequences of design errors and construction deficiencies.

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Alan Scott, FAIA, LEED Fellow, LEED AP BD+C, O+M, WELL AP, CEM, is an architect with nearly 30 years of experience in sustainable building design. He is a director with YR&G Sustainability in Portland, Ore. To learn more, visit www.yrgxyz.com and follow Alan on Twitter @alanscott_faia.

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