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Step by step (critical sequencing)

slaton patterson FAILURES
Deborah Slaton and David S. Patterson, AIA
The benefits of maintaining continuity and proper integration between varying components of the exterior building envelope are becoming better understood. Despite an increased level of awareness and improved specification language, detailing, and execution of critical interface details in the field, good intentions can still go awry if installation of various components is not properly planned and sequenced. Further complicating the move toward improving building envelope performance is that achieving better integration of assemblies often requires changing traditional thought processes of how building construction is sequenced.

For example, it is becoming more common for window and curtain wall assemblies in cavity wall construction to be integrated with the air/weather barrier through the use of transition membranes. This is easier to perform before other cladding systems are installed, unlike the more traditional approach in which windows and curtain walls follow the installation of the cladding that defines the fenestration opening. This change in sequencing can affect other work, and lack of proper advance clarification can result in resistance from the installer, poor execution of the detailing, and added cost.

This curtain wall assembly was designed to be integrated with the air/weather barrier via a silicone transition strip. Poor coordination and sequencing of the work resulted in the installation of the continuous cavity insulation and stone cladding before the transition strip was integrated with the barrier. This meant removing the stone, anchors, and cavity insulation to correctly complete the installation. Photo courtesy WJE
This curtain wall assembly was designed to be integrated with the air/weather barrier via a silicone transition strip. Poor coordination and sequencing of the work resulted in the installation of the continuous cavity insulation and stone cladding before the transition strip was integrated with the barrier. This meant removing the stone, anchors, and cavity insulation to correctly complete the installation.
Photo courtesy WJE

Installing fenestration before the cladding typically requires the former be protected from damage during installation of the latter. This is particularly the case when the wall assembly is masonry, which uses wet materials (e.g. mortar) and requires a wash-down following the work. Installation of the fenestration assembly must also be closely coordinated with that of the air/weather barrier, as well as any other accessories (e.g. cavity closures), for proper sequencing.

It is also necessary to determine which contractor installs which component. For example, although the transition strip engages the fenestration assembly, it is really an extension of the air/weather barrier and is generally best installed by the contractor responsible for the air/weather barrier—a division of labor that can generate much discussion if not clearly defined. Installing the fenestration before the cladding may also require a tightening of installation tolerances. Thus, without thorough planning and sequencing of the work, what might appear to be a simple, logical addition to integrate two adjoining wall components can have a significant ripple effect in the overall installation process.

To avoid sequencing problems in the field, the responsibilities for installation of various components and progression of the work must be properly specified and understood. An effective coordination/sequencing tool is the pre-construction meeting, in which all trades responsible for the various assemblies of the exterior envelope meet before the work begins and discuss how each aspect is to be coordinated with other adjacent construction.

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 dslaton@wje.com.

David S. Patterson, AIA, is an architect and senior principal with the Princeton, New Jersey, office of WJE, specializing in investigation and repair of the building envelope. He can be e-mailed at dpatterson@wje.com.

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