The Benefits of Building Envelope Commissioning
By Michael Nelson, CBST, guest author
This article is part of Wood Harbinger’s newsletter series.
The process of commissioning is typically associated with energy-related MEP systems like HVAC, domestic hot water, lighting, and potential renewable energy generation systems. However, building envelope commissioning is another path that can greatly improve building performance. Investing in a good envelope improves indoor comfort and air quality as well as HVAC system optimization. A building’s envelope is generally unchanged for the life of the building; building envelope commissioning is a proven process that helps maximize the chances of getting the envelope right.
What is Building Envelope Commissioning?
The building envelope commissioning program guides the envelope design with the question, “What should the envelope be?” It parallels the MEP commissioning process in many ways. The building envelope commissioning provider is an owner consultant, supporting the design team by developing the Owner’s Project Requirements (OPR); contributing to the Basis of Design documentation and specifications for Divisions 02 (existing conditions demolition), 07 (thermal and moisture protection), and more; and making recommendations to beef up the envelope above code minimum, which saves energy and improves comfort. The building envelope commissioning provider should be an expert in ASTM E2813 and E2947, the standard practice and guide, respectively, for building enclosure commissioning as well as National Institute of Building Sciences (NIBS) and ASHRAE standards and guidelines.
How Does Building Envelope Commissioning Work?
The building envelope commissioning program is not prescriptive; it’s calibrated to the OPR with a focus on the end game of making the envelope the best it can be rather than simply code minimum. During design review, the building envelope commissioning provider checks the architectural details, reviews the vapor barrier and air barrier definitions, and looks at cladding and the weather barrier. They also look at basic practical considerations, such as the chemical compatibility of proposed materials and whether the suggested adhesive will work with the envelope membrane.
During construction, the building envelope commissioning provider conducts regular site visits to verify the means and methods in practice, including review of construction sequencing and installation procedures, then developing inspection reports. They also verify the construction is meeting the design intent. A complex school (say 200,000 SF) would benefit from 10 site visits by the building envelope commissioning provider.
Like HVAC commissioning, building envelope commissioning isn’t a duplication or replacement for the contractor’s testing procedures; it is a means to develop guidelines for their testing and verify that it is completed as defined. For example, a good practice is to include air barrier testing performed by the contractor in the specifications. The building envelope commissioning provider defines in the specifications that this testing should be conducted by a qualified testing agency, holding the contractor to providing effective services. Similarly, for window testing, the building envelope commissioning provider would define in the specifications that an AAMA-accredited testing agency must perform this work, and then field verify that this happens. Using a certified testing agency may increase testing cost, but it saves a battle later on should the testing fail, knowing that a certified testing agency, held to the training and procedure requirements of that certifying agency, has done the testing. Other testing may include sealant pull tests, window assembly and roof integrity, and waterproofing. The type of testing should be scaled to the project complexity and risk/success factors.
After construction, the building envelope commissioning provider role winds down. They review the envelope and cladding maintenance documentation in the O&M manual, and check the cladding and seals around windows and doors during the post-occupancy evaluation.
Building Envelope Commissioning and LEED
LEED credits also illustrate the synergy between the building envelope and HVAC energy consumption. A good envelope controls air infiltration and exfiltration and improves thermal comfort, thereby reducing the work the HVAC system has to do. With a building envelope commissioning provider bridging communication between the envelope and HVAC system design, the HVAC equipment’s required size and capacity can be adjusted to work with the envelope. This saves the project first cost as well as operating cost, and, for projects pursuing LEED, more energy-efficient systems increase LEED credit points. LEED v4 now requires a review of the exterior enclosure design as part of the Fundamental Commissioning Prerequisite and must be commissioned as part the Enhanced Commissioning Credit Option Two. LEED v4 reduces the number of points affected by the MEP design, so earning two points with envelope commissioning is valuable.
Ongoing Efforts
Once the building is turned-over, the building takes on a life of its own and may start to deviate from the as-built condition as changes are made. Roof penetrations are a prime culprit: if someone needs an antenna on the roof, a new penetration is made in the roof, changing the design of the roof envelope. Over time, these modifications can have an impact on the longevity, comfort, and energy performance aspects of the building. Energy performance is a frequent telltale sign of potential envelope failure; increased energy usage may be a flag that additional investigation of the envelope is necessary, not just the system consuming more energy. Additionally, a building envelope evaluation should be a part of a comprehensive energy use investigation.
Existing building envelope commissioning, focused on the current facility requirements, should be conducted whenever a building’s use evolves. A prime example of this is the addition of air conditioning to a space not previously designed for it. A leaky envelope may not allow the A/C system to perform as intended. Interior humidity levels may rise and damage finishes. An investigation of the envelope to verify design assumptions may save costly corrections that lie ahead.
The Case for Building Envelope Commissioning
While retaining a building envelope commissioning provider’s services is an added project cost, the design reviews and construction inspections they provide help save money in the long run. Whether for new construction or renovation, building envelope commissioning helps maximize the chances that a building envelope will perform as intended and as needed.
Michael Nelson, CBST is a project manager with Intertek’s Building Sciences Group. He has 6 years of experience as a building enclosure consultant and field performance-testing technician. He has worked with Wood Harbinger on building assessment projects for the Port of Everett and we actively seek new opportunities to work together.