When a private developer charged Cuningham Group with designing the condominium buildings Indigo and Element on the same block in Marina del Rey, California, the studio assigned to the task expressed concern about diversity. If the two midrises were too similar, so the hunch went, they might cannibalize sales. Since Indigo already featured more traditional layouts, Element would include lofts to attract a different demographic.
Photo © A Wells
Cuningham partner and director of design Jonathan Watts explains the decision was more than a marketing ploy. Element’s lofts were intended to be the real deal—partition-free interior spaces with a service core that minimally blocks daylight or natural ventilation. And to guarantee that openness, Cuningham determined to use a concrete moment frame. The system is found in parking structures, Watts explains, or, thanks to concrete’s thermal mass, it is not unusual in the neighborhood of the architecture firm’s Minneapolis office. Yet in California, commonly a multifamily property is stick-built on a concrete podium, with plenty of shear walls.
Expense accompanied exception, and Watts estimates a surcharge between 10 and 15 percent for the moment frame. On the other hand, “Here we spanned 60 feet,” he says, “and, instead of us applying a layer of concrete surfaces to the structure, the system provided the interiors with all the finishes expected of a loft interior.” Offering more recompense, the concrete moment frame includes no seismic-resistant elements that might inhibit interior space planning.
Cuningham also figured on a sustainability benefit. The structural system permitted larger apertures in the exterior and more daylight to penetrate them, Watts notes, also saying of the material’s thermal mass, “Our climate is very temperate, and concrete reduces the building’s reaction to any environmental extremes.”
Indeed, Element’s 50 homeowners, most of whom took occupancy two years ago, report not using their air-conditioning. (Cuningham calculated zero cooling load, but the client installed systems as a precaution.) The building’s primary axis is east–west, and canopies mounted to the south elevation keep solar gain from overwhelming natural ventilation.
Watts acknowledges that the cement component of concrete has a significant negative environmental footprint. The design and construction team attempted lessening that impact by opting for precast concrete. Slabs and beams were “pulled” in double-T decks and finished to exact dimensions, avoiding waste. Fabrication took place only 50 miles from the project site, as well, and units were shipped to Marina del Rey and transferred to Element’s rising skeleton. In another example of one solution satisfying multiple demands, the choice of precast concrete was a boon for construction management: The urban site included no service circulation, so the use of a crane suited the tight space; it would have been more difficult to orchestrate crews pouring concrete.
When brittle concrete is chosen for a moment frame, special connections to attach horizontal and vertical components are required. Here, the custom joint is a series of sleeves and threaded rods welded onto the ends of the rebar that is cast inside beams and columns. The frame stands atop concrete spread footings, which are poured deeply enough to withstand punch shear. Crews brought up infrastructure with each floor of decking, and once all floors were installed and electrical and plumbing pulled through the platform, they roughed out the rest of building.
Watts says that erection of the five-story structure required only a few weeks of labor. Element’s concrete moment frame minimizes labor expenses in the future, too. “This is a 100-year building, and you’re not cluttering up the interior with walls and predetermined areas,” the architect comments. “Condos or housing may not be the highest and best use in the future, and because there are no shear walls, because you can clear out all the demising columns, the building can become an office or a warehouse or a post-production shop. It does not need to be demolished to be adapted.”