Proactive Service / Allegro Apartments

“ Over time I developed the deepest respect for the manner in which your company addressed issues head on, and always took full responsibility for their resolution in a manner that you could be proud of. Rather than "work to the rule," I found a willingness and a desire to see how you could exceed the standards set forth in the project documents. ”

Getting Steel and Wood Integration Right the First Time

The Challenge

The design of the Allegro is an urban industrial aesthetic. A highly articulated metal skin clads much of the structure. Brick and other masonry accents, and exposed steel and wood, particularly at the balconies, work effectively to create a modern residential character, convey the industrial aesthetic, and fit in well with the surrounding neighborhood.

Design of a new 297-unit apartment building dictated a structural system that was highly cost efficient. Wood framing over the concrete podium provided that cost efficiency. Given the intended height of the building, wood framing made tremendous sense, as it is used in four- and five-story multifamily buildings quite commonly today.

The combination of the aesthetic considerations of metal panels and metal details on an otherwise wood building created complex challenges that required close collaboration between Harkins, the design team, and the owner. Wood frame buildings are subject to more movement than concrete or steel buildings. They settle over time as the joints between all the individual wood components are compressed by the additional weight imposed during construction. In nature, wood maintains a very high moisture content. The milling and drying process removes much of that moisture as wood is prepared for its use in construction. Moisture is often is reintroduced due to exposure to the environment during the construction process. Eventually, over time, after the building is enclosed and the heating and air conditioning systems dehumidify the building, the wood again dries and incrementally shrinks, causing dimensional changes, particularly in the height of the building.

Metal panels and steel are rigid, and do not shrink or settle. Therefore, they must be designed to anticipate the shrinkage that will occur in the systems that provide their support. If there is no anticipation of these actions, destructive forces develop between the rigidity of the metal and the dimensional changes of the wood. These forces have dislodged cladding materials such as brick, and have even broken glass when they have not been appropriately anticipated.

The balconies on the Allegro were a specific point of concern in this matter. The typical balcony was framed with steel tubes connected to the wood framing. The exterior projection of the tubes supported a 12″-tall steel C-channel that formed a balcony skirt. On top of the skirt, a steel bar and pipe rail created the guardrail for the balcony. Infilling the tube steel, pressure-treated wood joists supported cedar decking and ceilings. The total weight of the average balcony approached 2,000 pounds.

This design element was a major feature of the project, and had the possibility of significant impact on the construction schedule, as well as the possibility of many unintended consequences. The interior portion of the tube steel, used to develop the cantilever, interrupted the normal locations for ductwork and sprinkler piping. Further, the impact of interior uplift in the floor structure as a result of the cantilever was a considerable concern. This was a highly atypical force to anticipate and contend with and required unique design of the floor truss system. The uplift concern was further evaluated to acknowledge that it would increase incrementally as construction activities added components to create the finished balcony. Adequate structural resistance to the uplift was crucial, to ensure that it did not cause a noticeable rise in the finish floor or damage to the cementitious gypsum underlayment.

The Solution

Harkins embraced this challenge as an opportunity. While excavation was still underway for the underground parking facility, a mock-up of the balcony system and a good portion of a typical unit was constructed in a barn belonging to the framing subcontractor – the first of many mock-ups on this job. The balcony mock-up went through many iterations as different elements were studied or added, including:

  • Supporting columns that were incorporated in the exterior walls
  • Internal supply ductwork
  • Bathroom, range hood, and dryer exhaust penetrations, which were all required in the wall surface and needed adequate separation and distance from operable windows and doors
  • Support for the sliding glass door
  • Waterproofing details where the steel would would penetrate the metal panel skin

Construction sequencing was an important part of the entire consideration. The structural engineer advocated stacking the steel channels on laminated wood columns, in order to most directly transfer the weight to the foundation. This requirement caused interference with the connection of the door headers and would have required that the steel tube be placed in the framing sequence, an operation that had the potential to significantly slow the carpenter down and add time to the construction sequence.

The Results

The results of the mock-up exercise allowed the expedient framing of the building and the installation of the steel tubes with minimal further carpentry required after their placement. In all but the most unique units, all production work for the mechanical, electrical and plumbing trades was installed in a well-coordinated fashion and a logical sequence, with a high rate of production that resulted from the knowledge developed. Savings were realized in both construction time and cost because the work was installed correctly the first time, and a consistent and attractive balcony system was installed that complemented the aesthetic characteristics of the building’s design.