In the second of this three-part series, we looked at creative applications of the code to address life safety and exiting requirements in existing buildings, while preserving historic resources and embodied carbon. This month we consider examples of multistory high-performance buildings where atriums provide daylight, natural ventilation and views. Sometimes the desired architectural expression and sustainability goals can be at odds with prescriptive code requirements. As you will read within each example, the critical smoke-control issues are addressed in radically different ways, by using advanced simulation tools to support creative approaches while also achieving the required compliance objectives.
The Delicate Dance of Code Innovations (Part 3)
The first project is the new Multnomah County Courthouse in Portland, Ore. Currently under construction, this 17-story, 460,000-square-foot building, designed by SRG Partnership with CGL Ricci Greene, includes courtrooms, civic spaces, administrative offices, secured sallyport, and detainee holding areas. One of the key features of the design is a welcoming, three-story public entry lobby with a grand stair leading to the third floor and offering sweeping views of the river and mountain beyond.
Multnomah County Courthouse, Portland, Ore. Image courtesy of SRG Partnership.
Ordinarily, a space like this is considered to be an atrium, which triggers a set of prescriptive code requirements including a smoke-control system. Such a system would require a smoke evacuation system ducted up through the roof, and controls that automatically open the lobby entry doors for air intake in a fire event. This would have added cost and created an unacceptable security breach, especially with the secure holding area located adjacent to the lobby for programmatic reasons. Code Unlimited took a fresh look at this challenge and developed a preferred solution in collaboration with the architects and Hoffman Construction (the general contractor).
They reclassified the space as a shaft (rather than an atrium), a penetration through multiple floors designed with two-hour separations to prevent the spread of fire and smoke to adjacent spaces. Most of the spaces adjacent to this grand lobby were already shafts (elevators, exit stair, etc.), so only a limited number of walls had to be upgraded to meet the separation requirements for this reclassification. A fire shutter was also added at the top of the grand stairs since these stairs were not required for means of egress. This solution required an appeal to the city’s board of appeals. Code Unlimited demonstrated the safety of this solution by using advanced computational fluid dynamics (CFD) modeling to simulate a fire in the lobby, and additional analysis to show that occupants in the lobby and in adjacent spaces were able to evacuate safely, especially because there was early visual notification of a fire to all the occupants in the public lobby.
The appeal was convincing, and it was approved. The solution preserved the architect’s design intent, avoided security issues, improved visibility from the building’s fire command center and saved approximately $100,000 (because smoke evacuation system was not required).
Atrium versus shaft diagram. Image courtesy of Code Unlimited.
The second project is a research and testing lab for a consumer products company. The four-story, 693,000-square-foot building wraps around a 7,800-square-foot, four-story atrium, capped by a saw-tooth roof with clerestory windows. In support of the owner’s sustainability goals, the atrium was proposed to be naturally ventilated with air inlets at the ground level and exhaust through operable clerestory windows and roof vents. Code Unlimited worked with the architect to develop a smoke evacuation system based on this passive design feature.
To refine the design and demonstrate to code officials that the solution was viable, they used Fire Dynamics Simulator (FDS) software developed by NIST, to produce a CFD simulation of a worst-case fire and the resulting smoke of the atrium. The biggest concerns in any atrium space are that the sprinklers are too far from the fire (32 feet above the source, in this case) to control it in a timely manner, and that the accumulating smoke prevents the occupants from safely exiting the building. Through the CFD modelling, the sprinkler activation was observed to occur only 216 seconds after ignition, controlling the fire and excessive smoke development so that occupants on all floors would be able to exit safely. The analysis showed that the saw-tooth roof form help to concentrate and direct of the flow of warm air and smoke, accentuating the natural stack effect of the atrium and reducing smoke accumulation.
Simulation tools help architects and engineers refine their designs for high-performance buildings, enhancing energy performance, daylighting, ventilation, and thermal and visual comfort. They are also critical to support non-traditional paths for code compliance, especially when unique design circumstances create conflicts between prescriptive requirements and design goals. Because of the gravity of potential consequences, the skillful application of modeling for code compliance is critical to convincing code officials that solutions are viable, and to refining the design for compliance. These tools support creative problem solving and ultimately lead to better solutions. As the examples presented in this column and in the last two months demonstrate, it is clear that the thoughtful application of building codes can have an important influence on sustainable design practices including building reuse, material efficiency and indoor air quality, while also protecting the health and life safety of building occupants.
Alan Scott, FAIA, LEED Fellow, LEED AP BD+C, O+M, WELL AP, CEM, is an architect with over 30 years of experience in sustainable building design. He is a senior associate with WSP in Portland, Ore. Samir Mokashi is the founder and principal of Code Unlimited in Beaverton, Ore. He has more than 25 years of architectural and code consulting experience, codeul@codeul.com. To learn more, visit https://www.wsp.com/en-US/services/built-ecology and follow Scott on Twitter @alanscott_faia.