Test of Time
Is it likely or even possible for a modern building to last for 250 years? Part of the Bullitt Center’s claim to the “greenest office building in the world” rests on the intention to make a building that will last much longer than the 73 year median for an office building in the US1
Bullitt Center under construction
Durability, longevity and environmental impact informed every decision about the materials to use in this building. In spite of the environmental impacts associated with Portland cement and concrete’s other constituents, there’s no viable substitute for a material that anchors the structure and holds back the earth, forms a cistern retaining up to 56,000 gallons of rainwater, transfers the loads of the upper portion of the building to the ground, and frames the primary public portions of the building’s ground floors. Made of the same material as the dome of Rome’s Pantheon, this building’s base and pedestal is likely to endure.
Bullit Center – Level 1
Floors three through six, topping out in the next month, are structured from timber and steel in a manner not seen in commercial office buildings in Seattle since the heavy timber mid-rise offices of the early 20th Century such as the Polson Building. Steel frames at the building’s core carry both lateral and gravity loads. Floor decks are made from 2”x6” boards laid-up vertically and nailed together to form a solid raft spanning 10’-6” between glulam beams. These beams are carried in steel “helmets” fitted into the tops of glulam timber columns, which rest in steel “buckets” at each floor level. A four inch concrete deck at each level, embedded with hydronic tubing that will circulate hot or cold water depending on the season, will serve triple duty as the finished floor, the heating and cooling system, and additional structural strength for the building.
Bullitt Center – Building the 5th Floor
Timber’s advantage over steel in this class of building is that it achieves the required fire-rating without additional materials to wrap and protect it. A steel beam exposed to flame will loose its structural strength before a comparable timber beam will. The timber ceiling, beams and columns will all be exposed as finished interior surfaces.
Bullitt Center – Level 4
While concrete is used purposefully for the building’s base serving at least triple-duty as retaining wall, water tank, and load-bearing frame, the timber used for the floors and frame of the upper levels has a smaller environmental footprint than concrete. Made exclusively of regionally sourced, FSC certified wood, this renewable material contains less embodied energy and has a smaller carbon footprint than concrete or steel in a comparable structure. In addition, it is a material that can more easily be re-purposed at the end of the building’s life.
But how much does durability really count in the actual longevity of a building? A study examining the demolition records for 227 buildings in Minneapolis2 challenges many common assumptions about building longevity, and, in particular, the relationship between structural material and service life. Although it is often believed that “durable” structural materials such as concrete and steel will provide the longest service lives for their buildings, this study found there is no significant relationship between the structural system and the actual useful life of the building. Building demolition is much more likely to be a function of changing land values, lack of suitability of the building for the current needs, and lack of maintenance of various non-structural components. Only eight buildings in this study identified “structural failure” as their reason for demolition.
Stewart Brand’s criteria3 for how well a building “learns” measures the likelihood for a building to adapt to changing needs and to remain useful over a long period of time. Brand describes buildings as nested systems or “shearing layers,” each with its own characteristic churn rate: site, structure, skin, services, space and stuff. Over the life of a building, the stuff and space plan go through nearly continual change, while the electrical and mechanical “service” systems go through more episodic renovation and replacement. The skin of a building might be renewed once or twice during a building’s life, but the elements most important to a building’s longevity are its structure and its relationship to the site.
With a robust, thoughtfully designed and carefully articulated structure, the Bullitt Center was designed to learn and to be adaptable over time. It’s durable structure and orderly geometry relate well to its site, its modular frame can be adapted to different space plans and uses, and it’s size is predictive of the scale and density of development in the Pike-Pine district, making it likely to serve the community’s needs well into the future. It is easy to imagine the building adapting as necessary to residential, commercial or institutional uses. So in addition to its durability, its longevity will be determined by its ability to learn, to adapt to changing uses, and to stand the test of time.
1Buildings Energy Data Book, Buildings Technologies Program, Energy Efficiency and Renewable Energy, U.S. Department of Energy, page 3-12.
2O’Connor, Jennifer. Survey on Actual Service Lives for North American Buildings. Presented at the Woodframe Housing Durability and Disaster Issues Conference, Las Vegas, Nevada, October 2004.
3Brand, Stewart. How Buildings Learn. Viking Press, 1994
Rob Peña is an Associate Professor in the Department of Architecture at the University of Washington where he teaches architectural design studios and environmental control systems courses with an emphasis on ecological design and high-performance buildings.
PHOTO CREDITS: John Stamets
John Stamets teaches photography and runs the Architecture Photo Lab in the basement of Gould Hall. Stamets also runs the Architecture Photo Lab, which is open to all students in the CBE for the purposes of photographing models, art work and other built objects.