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Building Envelope Commissioning - Saves Money & Energy
Studies have shown that as much as 40 percent of energy consumed by buildings is through air leakage. Air leakage reduction is now considered as important as thermal insulation. Substantial energy loss through the building envelope (roof, walls, windows and floors) can contribute to condensation/water, mold and structural deterioration. However, the potential for these problems can be lessened through building envelope commissioning, or "BECx," which strives to improve the quality and performance of building envelopes. To understand BECx, consider the following facets of testing and inspections:
Geographic Analysis
Temperature and humidity vary greatly depending on whether you are in the Upper Midwest temperature extremes or the hot and humid coastal regions of the southeastern United States. Because buildings react differently in these varying temperatures and humid conditions, designers and contractors need to understand how the occurrence of vapor migration, dew points and air/water infiltration can affect building performance. Knowing your location means understanding these variables and how they can affect the performance of your building. In northern climates, vapor barriers combined with adequate wall and roof insulation are needed to help prevent vapor transmission through wall assemblies. Vapor transmission that passes through the wall assembly can condense within the cavity potentially causing moisture issues that could lead to structural problems. These barriers are typically installed on the interior side of the wall. Conversely, in southeastern climates, the vapor barrier is required on the exterior side of the wall assembly to stop the warm, humid air from migrating into the wall cavity.
Peer Reviews
Performing a design analysis of wall and roof assemblies can provide information about the temperature gradient through the construction materials. This helps to identify the dewpoint within the walls at different times during the year. The designer can then use this information to place the vapor barrier in the correct location to prevent vapor migration and condensation inside a wall. A peer review focuses on wall and roof penetrations and material transitions. Windows are a critical part of wall systems and one of the least understood systems. BECx peer reviews examine window flashings and drainage systems, and the materials and components used within these systems. Identification can be made on the drainage plane to verify that wall systems can drain away water that might seep behind sealants or through joints in the exterior cladding system. Typical oversights include missing thru-wall flashings at the base of walls, flashings at material transitions, and reliance on a caulk joint around windows and at edges of cladding systems as the only barrier against water intrusion. A peer review can identify these issues and may result in additional recommendations or technical support for improvement.
Constructability Reviews
Open communication between designers and contractors is essential. Designers cannot detail every condition, yet every project reaches the point where the contractor has to make a decision about how to seal a flashing or terminate a material. Typically, the results of in-field decisions are quickly covered up by finish materials and forgotten about until a water leak is discovered. Constructability reviews are used to examine key details of the construction and the step-by-step process required to complete the installation. The BECx representative works with the designers and contractors to help them understand correct installation procedures so the envelope may perform as intended. Mock-up testing allows the contractor to evaluate the performance of the construction early in the process (when there is still time to make corrections). Mock-ups can be free standing models or a section of the actual building wall that contains one or two typical window types, the air barrier, penetrations (such as exhaust vents or masonry anchors), finished cladding material and thru-wall flashings. Typically the interior window trim is not installed so the joint between the window and rough opening can be inspected during the testing. Mock-up testing follows ASTM standards for water penetration and air infiltration through windows and the surrounding walls.
Construction Inspections
Periodic inspections of the exterior walls and roof during construction can lead to better installation. Inspections must be timed to observe window or flashing installations before they are concealed. Likewise, roof inspections help monitor the installation progress and quality control. Final Building Performance Testing The U.S. Army Corps of Engineers (USACE) has implemented stringent requirements for testing air leakage in buildings as part of final acceptance. Contractors working on USACE projects understand the importance of implementing a building envelope commissioning process for success in the final air leakage test. Building air leakage testing, which follows ASTM and USACE test protocols, involves pressurization or depressurization of the building utilizing numerous pressurization cycles at incremental pressure settings. Blower door panels are set up with one, two or three fan configurations, depending on the size of the building. The total surface area of the pressure boundary (or air barrier) is used to calculate the maximum airflow required to achieve the maximum pressure in the building. Upon completion of the pressure cycles, a calculation is done to determine the air leakage in CFM (cubic feet per minute) per square foot at the specified building pressure. A calculation can also determine the total surface area of air leakage in the total building. If a building fails the air infiltration test, the BECx agent can use infrared thermography and smoke tracers to locate air leaks in the building envelope.
Conclusion
Building envelope commissioning is gaining acceptance as designers, contractors and building owners begin to understand the value added to their projects. The process promotes better design and higher quality construction, which results in more energy efficient buildings, reduced water infiltration, condensation and mold problems in buildings, and more comfort for occupants. This can mean energy savings, fewer contractor call-backs and warranty claims, and reduced operating costs.
 Ron Reigle, AIA
Braun Intertec
11001 Hampshire Avenue S | Minneapolis, MN 55438
800.279.6100 Toll Free | 952.995.2020 Fax
RReigle@braunintertec.com
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