Deborah Slaton, David S. Patterson, AIA, and Kenneth M. Itle, AIA
Replacement windows present challenges in terms of installation and anchorage, especially in ensuring resistance to air and water infiltration and providing reliable structural support. In a 1910 midrise, a former industrial building, new windows were installed within the exterior façade consisting of brick masonry and an exposed concrete structural frame. In this building, brick masonry is used as partial-height spandrel walls below the windows and extends between adjacent concrete columns. Replacement windows were installed approximately 10 years ago, at which time the window openings were made taller to accommodate the larger units. The windows were also provided with new sills closer to the floor level by removing masonry below the original sill location.
During a recent water leakage investigation, the removal of interior finishes revealed conditions related to the replacement window installation. The windows are aluminum-framed, single-hung units. They were installed directly into the rough opening without a new sub-frame. The original exterior wall construction included a 25-mm (1-in.) deep reveal in the concrete structural columns, into which the middle wythe of the three-wythe brick masonry was keyed to provide lateral stability for the brick infill panel. When the window rough opening was enlarged to accommodate new units, a simple sawcut was made in the brick infill wall. The masonry remnants extending into the column reveal were ignored and left in place.
The new windows were anchored with a series of multiple light gauge clips and small diameter screws, fastened directly to the frame and the adjacent concrete or masonry. At the upper half of the new window, the fasteners engaged the structural concrete column, and at the lower half, the fasteners extended only into the brick and mortar remaining within the column reveal. The brick and mortar remnants have deteriorated and are unstable. Therefore, the window anchorage for the lower half of the window is considered unreliable. Repairs will involve removal of the windows, repair/replacement of the brick masonry, and reinstallation of the window unit with appropriate fasteners that are sufficiently long to engage the structural concrete.
In contrast, another installation of new aluminum-framed windows in an existing concrete and masonry structure benefitted from proper detailing. Prior to large-scale project implementation, a mockup installation was performed. The mockup process included removal of non-original older windows, exposing abandoned remnants of the original window system as well as the true profile of the structural concrete surround. The stainless steel anchorage for the new window was then designed to accommodate both the new window system and the configuration and condition of the structural substrate.
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.
Kenneth M. Itle, AIA, is an architect and associate principal with the Northbrook office of WJE, specializing in historic preservation. He can be reached via e-mail at firstname.lastname@example.org.