Expanding focus on movement

FAILURES
Deborah Slaton, David S. Patterson, AIA, and Jeffrey N. Sutterlin, PE
Many building components (including the structure itself) are required to accommodate in-service dimensional changes associated with thermal and moisture variations, as well as reversible and irreversible movements created by other types of structural and environmental loadings. Unfortunately, the focus on accommodating such movements is often limited during the design and construction phases. Inattention to these issues can result in certain movements being inadequately accommodated, or the realization during construction that movement provisions must be incorporated into the building—a process that can be frustrating, time-consuming, and costly.

Accommodation of thermal- and moisture-related movements in exterior cladding components or systems seems to be better understood by both designers and the construction trades, as these are common elements found in most building types. Trade associations such as Brick Industry Association (BIA) and National Concrete Masonry Association (NCMA) provide guidance regarding proper spacing, locations, and size of expansion joints (clay masonry) and control joints (concrete masonry). Similarly, many manufacturers of aluminum-framed curtain walls, storefronts, skylights, proprietary panels, and other claddings offer guidance on the proper design and placement of movement joints within their assemblies.

Joints within cladding systems are also typically addressed during design development because they can have an impact on building aesthetics. It is therefore incumbent on the designer to understand limitations of these products/systems and appropriately locate movement joints; further, the mechanic installing the cladding must incorporate the movement joinery as intended to ensure a serviceable assembly.

In contrast, structural movement joints can often be much more complicated to understand and incorporate. These joints provide a clear separation of the building structure and/or separation between the existing and the new construction, and are intended to accommodate both thermal and dynamic movement of the structure. These joints can take on complex geometries and configurations; they can provide clear separation of structural elements or, in some cases, slip joint connections where the movement joint above one support member is offset with the joint at the member below.

Since structural joints need to be continuous around the building enclosure, without any discontinuities or bridging of the joint, numerous materials in both horizontal and vertical planes are typically involved, including roofing/waterproofing membranes, air/vapor barriers (AVBs), claddings, and, in some cases, floors. As such, these joints need to not only accommodate building movements but also serve as barriers to air infiltration and water penetration.

Apart from location, the detailing of these joints is rarely fully developed or coordinated between the architectural and structural designers, or between trades installing adjacent systems. In some cases, horizontal and vertical expansion joints are addressed under two different specification sections; they may also be purchased from, and installed by, two different trades, making coordination even more critical—the result is often installation challenges and warranty issues.

Deferring the detailing of these joints to be resolved in the field can result in additional work, such as the modification of existing construction to accommodate a pre-manufactured joint. It can also create difficulties with schedule and budget, as pre-manufactured joints may require a custom order with significant lead times.

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.

Jeffrey N. Sutterlin is an architectural engineer and senior associate with WJE’s Princeton office, specializing in building envelope investigation and repair. He can be reached at jsutterlin@wje.com.