POSTED ON December 10, 2015
|Photo courtesy of ZGF Architects LLP|
Building envelope commissioning (BECx) is of growing interest to the building design industry because of increased focus and ambition on building energy performance, along with concerns about the quality and durability of building enclosure components due to enclosure failure. BECx encompasses all building enclosures including roofs, walls and fenestrations. Here are seven important things to know about building envelope commissioning:
According to the National Institute of Building Sciences (NIBS), the BECx process validates that the design and performance of materials, components, assemblies and systems achieve the objectives and requirements of the building owner. This process achieves this through experience, expertise, modeling, observation, testing, documenting and verifying materials, components, assemblies and systems to validate that their use and installation meet the owner’s requirements to create a high-performance envelope.
“Architects are designing better buildings through BECx because they now can gain a better understanding of how various components within the enclosure affect other critical assemblies,” says Jeff Crowe, PE, BECxP, project manager, Pie Consulting & Engineering, Denver. “For example, architects can assess how metal panels and their connections will impact the performance of the weather-resistive barrier (WRB) or thermal barrier. Some metal panel connections and penetrations through the WRB may create the potential for water leakage through exterior walls. With BECx, an architect can define specific performance criteria for the wall assembly and require testing that verifies that performance is being achieved.”
There are two detailed industry guidelines that describe BECx: The National Institute of Building Science Guideline 3-2012 (NIBS GL 3) and ASTM E 2813-12 Standard Practice for Building Enclosure Commissioning. Architects need to know what these industry standards require and have a basic idea of how BECx will impact a project. Crowe believes that while NIBS GL 3 is a more descriptive guideline, it is somewhat unclear with respect to the required performance testing. “ASTM E 2813, on the other hand, is shorter and less comprehensive, but provides clear direction as to the required testing for differing levels of BECx,” he says. Additionally, LEED v4 includes prerequisite options for fundamental and enhanced BECx. “The emphasis on building performance is seen in the new LEED v4,” says Chris Chatto, principal, ZGF Architects LLP, Portland, Ore. “It explicitly rewards projects which adopt envelope commissioning, as well as the rise of passive house construction in the United States, which requires certification infiltration performance testing to meet a rigorous infiltration standard.”
|Photo courtesy of Simpson Gumpertz & Heger Inc.|
Prior to starting any construction activity, BECx requires serious forethought in the design phase. Understanding early on the implications of detailing and complexities of material transitions and intersections is critical for the successful performance and commissioning of the envelope. Also, it is less complicated and less costly to repair building enclosure problems before they start, before they spread and before they pose a risk to occupants.
The first step in the BECx process is to define the building owner’s project requirements (OPR) via performance metrics. “Some requirements may be as basic as providing an airtight building,” says Andrew Dunlap, AIA, principal, Building Technologies Studio, SmithGroupJJR, Detroit. “Sounds simple enough, right? Well, airtight must be further defined. Most buildings will experience some amount of air leakage. The key is to define the level of air leakage that is acceptable. Requirements may address other topic areas such as watertightness, energy performance, safety and security, and long-term durability to name just a few.”
An OPR document serves as a starting point for the design team to develop the basis of design. Consider it a living document that may be continually updated throughout the design process. For instance, an owner could find out his requirements are quite stringent and might have significant cost impacts. The OPR can be modified by the owner and commissioning team to address owner desired changes.
But preplanning doesn’t end at the OPR. Engage contractors and installers in the design phase to ensure constructability in the field. “Also, it is important to consider sequencing of commissioning activities,” says Chatto. “Preliminary tests should be performed at intervals where remediation and repair, if required, can be completed without unnecessary alteration of installed skin and cladding systems. A rigorous on-site quality-control process is necessary to ensure not only that envelope components are installed correctly, but also to ensure that those components are not damaged in subsequent construction phases. This ensures that the tested results remain relevant and final commissioning tests are successful.”
|Photo courtesy of SmithGroupJJR|
Documentation beyond the OPR throughout the BECx process is also important. Unlike commissioning of other building systems, BECx must account for materials and assemblies that are often designed by various parties, manufactured by different companies and installed by different trades people on-site. “Every decision and change that impacts the enclosure must be documented and distributed so that all of the various parties understand how the building enclosure and the OPR are affected,” says Crowe. “Tools for documentation generally include BIM360 Field, Bluebeam and other platforms.” Throughout the design process, the commissioning team should perform periodic reviews of the design documents to verify that the design is in line with the OPR.
BECx validates and verifies the performance of enclosure systems through performance testing. The testing requirements are developed early in the BECx process and must be met by means of mockup or in-situ testing of building enclosure assemblies. “Typical performance tests include ASTM E 1105 for water penetration of fenestrations and claddings, ASTM D 7877 for leak detection of waterproofing membranes, and ASTM C 1153 for locating wet roof insulation,” says Crowe. “BECx also provides an avenue for building owners and operators to monitor the building enclosure by means of a system manual that clearly indicates the assemblies within the enclosure and spells out anticipated maintenance schedules.”
Building enclosure commissioning is handled differently than traditional mechanical system commissioning. While mechanical equipment can typically be accessed, tested and adjusted after installation, building enclosure components (waterproofing membranes, air barriers and insulation) are typically concealed behind finish materials.
“It is difficult and potentially costly to make adjustments or repairs if the enclosure components are not properly designed and installed initially,” says Emily R. Hopps, senior project manager, Simpson Gumpertz & Heger Inc., Waltham, Mass. “This makes it critical to review the enclosure during the design and early construction phases.”
Peter M. Babaian, associate principal, Simpson Gumpertz & Heger Inc., Chicago, agrees that enclosure commissioning is intended to be a process, beginning in the pre-design phase and continuing through design, preconstruction and construction phases of the project. “BECx will not be effective if it is implemented as a series of isolated activities; it must be an ongoing and continuous review and verification throughout the entire design and construction cycle,” he says. “Limiting enclosure commissioning to performance testing during the construction phase of the project risks investing time and resources into installations or systems that are inherently not capable of performing to project requirements.”
|Photo courtesy of Pie Consulting & Engineering|
Envelope air barriers produce substantial energy savings, reducing moisture damage and improving interior air quality. Their design, coordination and testing are key elements in a multi-component building commissioning enclosure strategy. Not surprisingly, it was ASHRAE that published the first building commissioning guide “HVAC Commissioning Guide” in 1988.
Metal enclosure systems require careful consideration of materials compatibility; integration with back-up waterproofing, air, vapor, and thermal barrier systems; and attachment design. Hopps notes these items can be reviewed and vetted through the commissioning process and through the use of mock-ups.
Fred Rose, president of Fred Rose LC, a Butler Builder in Cedar Falls, Iowa, believes when commissioning a building envelope, minimize the variables that could impact a building’s thermal performance as it moves from design to reality. “Pre-punched metal panels help provide an insurance policy that the building is going to go up the way it is supposed to, so architects can rest assured that there won’t be construction challenges or workarounds that hinder performance once the building is complete,” he says. “Because thermal efficiency is not homogenous across the variety of building materials used in a facility, the insulating values of one material may be compromised by an adjacent weak link that creates a thermal short circuit. Using building assemblies that have been tested will also help avoid any surprises after construction.”
“Once the air and vapor barrier detailing and materials have been determined, the design team should coordinate barrier membrane interfaces with the responsible subcontractors and suppliers, the earlier the better,” says Steve Fronek, PE, vice president of technical services, Wausau Window and Wall Systems, Wausau, Wis. “Ensure that sequence of installation is workable, and ideally, does not depend on the window installer to complete the waterproofing contractor’s work.” Fronek believes other design criteria for air barrier tie-ins at window and curtainwall perimeter details that must be stressed in the BECx process include:
• Attachments must accommodate shimming, adjustment, anchorage and building movement
• Connections must maintain continuity of air/ water/vapor permeability
• Thermal “short circuits” must be avoided
• Flashings must drain effectively
One of the primary benefits of the commissioning process is its peer review aspect. “The peer review of the design documents can have benefits that far exceed the particular project that is being commissioned,” says Dunlap. “The design team can take what they have learned and apply it to future buildings. The ripple effect that peer review can have will hopefully be quite significant.”
Exterior enclosure commissioning is not a new development. This type of work has been performed for well over 20 years (if not many decades longer) but Dunlap feels it has often been completed under the guise of Peer Review. “The commissioning aspect may be a relatively recent development that starts to provide an organized baseline framework from which to work,” he says. “One primary item to understand is to not be overwhelmed by commissioning. It can be and should be tailored to every project. Each project has specific needs and the level of commissioning needed must be appropriate to that project. Even if a formalized commissioning process is determined to not be necessary, consider employing a peer review process to ensure that your design is responding to the owner’s desired outcome.”
|The University of California at Berkeley’s Energy Biosciences Building, Berkeley, Calif., is made better via envelope commissioning, which includes an air barrier.|
|Images courtesy of Wausau Window and Wall Systems,”after” photo by Bruce Damonte.|
Reference: Metal Architecture By Mark Robins, Senior Editor, Posted 12/01/2015