LEED Envelope Commissioning (Enclosure Commissioning)
What is Envelope Commissioning or Building Enclosure Commissioning (BECx)?
Most of us have heard of Commissioning (Cx) as it deals with HVAC equipment and digital controls. But what is “Enclosure Commissioning” or “Envelope Commissioning,” and what about LEED Envelope Commissioning? Its scope is vast and skills and knowledge required are pretty intensive as well.
LEED v4 has really cast a spotlight on Enclosure Commissioning or ‘BECx’. NIBS guideline 3, available for free online National Institute of Building Sciences = NIBS lays out the full scope of BECx across all phases of a project, starting from early design (Schematic Design or perhaps even Predesign) to end of construction and then into the occupancy phase. It provides a detailed list of all the activities performed at each stage and explains the roles and responsibilities of the BECxA in every phase. ASHRAE Guideline 0-2005 talks about Cx in broad, general terms and is applicable to both HVAC as well as Building Enclosure Cx. ASTM E 2813-12 specifically addresses BECx but is not free.
The NIBS team decided early on that the “E” in BECx would stand for “enclosure” not “envelope” as the latter sounds too much like stationary. Hence BECx is officially “Building Enclosure Commissioning” not “Building Envelope Commissioning.”
AIA also provides a standard contract for BECx services
While BECx begins in schematic design, the work can essentially be boiled down to building science + building testing. Building science involves studying the flow of heat, air and moisture across all 6 sides of the building enclosure – the walls, roof and slab. In order to do this, the different layers in the building skin are (theoretically speaking) divided into weather barrier, air barrier and thermal barrier. Vapor barriers are best avoided in all climates except the coldest regions. E.g., the ply sheathing is the air barrier, building paper is the weather resistive barrier and insulation is the thermal barrier. These 3 barriers need not always be separate – sometimes they come together as in an insulated glazed window wherein the IG plays the role of all 3 barriers. The next step is to ensure continuity from top of parapet to the bottom of the footing for all 3 barriers, despite openings, penetrations, material changes etc. In order to accomplish this continuity, it is important to be able to draw a continuous line through the full height of the exterior wall section without lifting your hand from the paper. You also have to repeat this exercise in plan view across various conditions. In addition to this, the BECxA also reviews the drying potential of the wall and roof assemblies and reviews each condition for water intrusion, much like a water proofing consultant. But unlike the water proofing consultant, the BECxA reviews water proofing for air-transported moisture as well, in addition to rain and wind driven moisture, capillary action and vapor diffusion.
The other significant aspect of BECx scope is building testing
Many of the tests are performed on construction site mock-ups, while some such as the blower door are performed once the building is complete.
NIBS guideline 3 puts the fees for full BECx scope at 0.3 – 1% of project budget.
The main incentive for BECx on projects thus far, has not been LEED but the need for a high performance building. Most BECx projects are located on the east coast or harsher climates than ours.
I completed a course offered by the University of Wisconsin on BECx in order to become a BECxA. The University is slated to come out with a more comprehensive, better course later in 2014, which I’m considering as well. But the fact that I have been studying building science for many years now and have 17+ years of experience as an architect in the Bay Area with experience in just about every type of building construction and sector, helps me tremendously in my work as well.
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