Deborah Slaton, David S. Patterson, AIA, and Jeffrey N. Sutterlin, PE
When properly specified and executed, the preconstruction performance mockup of an enclosure assembly can offer several benefits to any project. Most notably, the mockup provides project teams the opportunity to observe, evaluate, and refine the design, fabrication, and installation sequencing of the enclosure assemblies and corresponding interface conditions.
The more obvious goal of a performance mockup is to verify the constructed enclosure satisfies the performance requirements identified in project specifications when subjected to simulated wind, air, and, in some cases, thermal loadings. A less acknowledged (but equally important) goal of the performance mockup is to review installation workmanship, sequencing, coordination between trades, and quality assurance/control (QA/C) checklists before start of construction; through this secondary goal, the opportunity exists to improve detailing, constructability, and collaboration between key trades.
For a performance mockup to provide the value and benefits noted above, detailing of the tested assemblies must be identical to the systems installed on the project—including installation in the same manner and sequence as on the project, and, ideally, by the same mechanics. Any variation in detailing between the approved performance mockup and the actual building construction can result in a condition that compromises the performance of the installed assemblies.
During recent construction of a multistory office building that included punched storefront windows surrounded by aluminum composite metal panels, a standalone performance mockup of the punched window and surrounding opaque wall assembly was successfully tested to resist water penetration when subjected to a static air pressure differential of 575 Pa (12 psf), satisfying the project requirements. However, during installation on the building, significant modifications were implemented in the window installation sequencing (the changes affected the placement of critical seals between the subsill, framing, and opaque wall components). This change, thought to be inconsequential, was implemented to allow the windows to be installed from the building interior, rather than the exterior as was the case during the construction of the mockup—reportedly to allow for a more cost-effective installation.
Fortunately, this project also required in-situ field performance verification testing of the installed windows, which resulted in widespread water leakage at all windows tested prior to applying a pressure differential across the plane of the test specimen. Further diagnostic testing determined a critical seal at the frame/opaque wall interface had not been installed—this seal was included in the performance mockup but omitted in the windows installed at the building due to sequencing issues. Since the first iteration of in-situ field performance verification testing was performed relatively early in the construction process, the missing seals were identified early in the process and sequencing of the work corrected, resulting in no schedule delays or significant remedial costs. The installed assemblies met the specified 575 Pa air pressure differential during the subsequent in-situ testing, highlighting the importance of being faithful to the performance mockup during installation on the building.
The opinions expressed in Failures are based on the authors’ experiences and do not necessarily reflect those of The Construction Specifier or CSI.
Deborah Slaton is an architectural conservator and principal with Wiss, Janney, Elstner Associates (WJE) in Northbrook, Illinois, specializing in historic preservation and materials conservation. She can be reached at firstname.lastname@example.org.
David S. Patterson, AIA, is an architect and senior principal with WJE’s office in Princeton, New Jersey. He specializes in investigation and repair of the building envelope. He can be reached at email@example.com.
Jeffrey N. Sutterlin, PE, is an architectural engineer and senior associate with WJE’s Princeton office, specializing in investigation and repair of the building envelope. He can be reached at firstname.lastname@example.org.