by Brian H. Neely, AIA, CDT, BECxP, and Edward J. Stewart, RRC
The long-term performance of any exterior building enclosure assembly is directly related to the level of planning implemented during the initial phases of the design process. It requires the combined efforts of the owner, building enclosure commissioning provider (BECxP), design team, and contractors.
Commissioning consultation services typically begin during the creation of the owner’s project requirement (OPR) document. The services continue through peer reviews of the building enclosure specifications and drawings at each design stage, focusing on the enclosure’s ability to resist moisture intrusion and air infiltration, and to maintain a continuous thermal enclosure. Extending into the construction process, the BECxP (hired by the owner in the majority of instances) oversees peer reviews of the shop drawings and contractor coordination meetings, and performs periodic site observations and mockups/in-field testing to confirm the performance capability of enclosure components.
Building enclosure commissioning can often help avoid common issues in building construction, such as water intrusion, which frequently results in indoor air quality (IAQ) concerns, mold growth, air infiltration, and associated energy loss. There are countless examples of enclosure failures that cost owners, insurance companies, and contractors millions of dollars to remedy the resulting mold and moisture problems. The BECxP can identify design and construction issues at a significant discount as the costs for building enclosure commissioning services are generally but a small fraction of the potential repair costs.
Building enclosure failures
When it comes to remaining dry and comfortable, many new buildings fail to perform as well as expected. Enclosure leaks and/or air infiltration are among the primary cause of lawsuits against design architects. Once construction starts, the contractor is mostly focused on constructing the building in accordance with the drawings while remaining on schedule and within budget. It is the BECxP’s responsibility to maintain the team’s focus on the proper construction of the critical weather, vapor, and air barrier components of the enclosure.
Some of the key causes of enclosure failures include:
- reliance on a single rainwater barrier;
- new untested building materials;
- complex geometries;
- repetitiveness of problem details;
- lack of technical understanding of moisture intrusion mechanisms;
- lack of understanding of inter-relationship with HVAC systems;
- lack of modeling/review/testing/startup; and
- lack of defined expectation of the building’s performance with regard to the selection of materials and details.
Building enclosure commissioning has become more common since 2000. Since the turn of this century, there has been a push for tighter buildings with the introduction of air barriers into the building codes, as well as the introduction of sustainability guidelines, such as the Leadership in Energy and Environmental Design (LEED) rating system. The inclusion of air barriers promised energy savings and higher performance buildings. Instead, the new science was not understood by the designers or installers, and small defects in the exterior enclosure led to significant moisture, mold, and IAQ problems. Air leakage and poor connectivity of enclosure assemblies created a situation where buildings were not meeting the promised performances.
Evolution of enclosure commissioning
With this history of moisture intrusion in buildings, commissioning of the building enclosure became more important to address infiltration issues before project completion. Building enclosure consultants turned to HVAC commissioning, which had been successful over the previous decade. As a process, building enclosure commissioning follows a similar pattern as HVAC commissioning:
- identification of the project performance objectives;
- design-phase peer reviews; and
- construction-phase inspections and testing.
However, for the building enclosure, there is typically nothing comparable to the test and balance and other functional test procedures routinely specified in contract documents for HVAC systems. Further, while HVAC systems can be tweaked and fine-tuned once the building is completed, waiting until construction is complete to test the building enclosure is too late because the façade components are already in place.
The American Society of Heating, Refrigeration, and Air-conditioning Engineers (ASHRAE) Guideline 1-1996, The HVAC Commissioning Process, had been in place for 20 years to help engineers and owners properly design, construct, and test HVAC systems in buildings. In 2006, the National Institute of Building Sciences (NIBS) issued a Building Enclosure Commissioning Design Guide that described the specific application of the commissioning process, laid out in ASHRAE Guideline 0-2005 as it pertained to the building enclosure. This guideline was updated in 2012. At this time, ASTM International released ASTM E2813, Standard Practice for Building Enclosure Commissioning, which defined the practice of building enclosure commissioning and identified the minimum requirements for two specific levels of commissioning: “Fundamental” and “Enhanced.”
Following the publication of ASTM E2813 in 2012, ASTM and NIBS entered into a memorandum of agreement, part of which required the NIBS guideline be developed and published as an ASTM standard guide. This was published as ASTM E2947, Standard Guide for Building Enclosure Commissioning, in 2014.