It’s often tempting to reach into the digital archive and rehash an old detail. For the sake of the planet—and your own career—please stop. If it doesn’t minimize operational and embodied carbon, it’s got to go. The details described and shown below, by contrast, are taking steps in the right direction.
Rwanda Cricket Stadium, Kigali, Rwanda
Detail: Vault section at footing
Firm: Light Earth Designs, Cambridge, England
Description: Handmade by local workers using mostly local materials—hydraulically pressed soil and broken granite—this trio of open-air tile vaults assumes a parabolic geometry that puts the structure entirely in compression, masonry’s strong suit. At just 250 millimeters (10 inches) thick, the vaults span up to 16 meters (52 feet). Also noteworthy, says Light Earth Designs founding partner Michael Ramage, is the use of a flexible polypropylene grid instead of reinforcing steel for seismic resistance. Because the grid is sandwiched between each tile course at the vault-and-pier connection, the construction team built temporary framework to hold the structure in place until the concrete set. “Changing the mode of operating and thinking isn’t hard,” Ramage notes, “but it does require some concentration.”
Performance Highlight: “Two people with a van can carry a 300-square-meter roll of geogrid, further reducing its embodied energy from that of steel mesh. Overall, the tile vaults have approximately 75% less embodied carbon than if they were built using reinforced concrete,” Ramage says.
Tufts University Science and Engineering Complex, Medford, Mass.
Detail: Exterior wall section at spandrel panel
Firm: Payette, Boston
Description: Full-height glazed curtain walls abound in all climate zones, desired for their ability to let in daylight and visually connect the indoors and outdoors. At Tufts University, Payette strategically inserted a glass box between two historical red brick buildings—one of which the institution had proposed demolishing or relocating. The result is a singular interdisciplinary research hub that Tufts plans to own and operate for the next 100 years or more. “You want the insulation as close to the glass as possible,” says Payette principal and building science director Andrea Love, AIA, without creating a large temperature differential between components or building up heat behind the wall. The detail uses mineral wool insulation, which has a lower embodied carbon than extruded polystyrene (XPS) and polyisocyanurate, though options with even lower embodied carbon could be potentially specified.
Performance Highlight: “As built, this detail achieved an R-value of 15.6, about 160% higher than a traditional spandrel panel,” Love says.
Project Name Withheld, East Coast, United States
Detail: Conventional versus optimized plaster over metal-stud rainscreen
Firm: McLennan Design, Bainbridge Island, Wash.
Description: For this zero-net-energy project, McLennan Design is putting its ongoing research of sustainable materials into practice. “Having an innate understanding of where embodied carbon comes from more fully allows you to come up with custom details for specific projects and locations,” says designer Brad Benke, AIA. By undertaking these studies, he adds, architects can pinpoint missing industry data, encourage more manufacturers to publish Environmental Product Declarations, and “drive market change for lower carbon solutions.” In these details, the firm discovered that switching the insulation material provided the greatest reduction in embodied carbon, while the plaster finish had the highest individual contribution. “We are now investigating ways to reduce the cement/lime content of the plaster while still maintaining performance,” Benke says.
Performance Highlight: The optimized wall assembly reduces embodied carbon by 22% without compromising thermal performance. “Almost any cladding material could be used” with this wall assembly to achieve similar results, Benke says.
Bed-Stuy Passive House, Brooklyn, N.Y.
Detail: Traditional versue Passive House masonry wall retrofit
Firm: Co Adaptive Architecture, Brooklyn, N.Y.
Description: For the renovation of their own brownstone, Co Adaptive principals Bobby Johnston, AIA, and Ruth Mandl, AIA, used no fewer than four insulation types. At an equivalent R-value, mineral wool has a lower embodied carbon impact than XPS, expanded polystyrene, polyisocyanurate, and spray foam, while cellulose is considered to have a negative embodied carbon impact. Wood fiberboard can be substituted for XPS, but Johnston has yet to find a non-foam structural insulation. A continuous "smart" air and moisture control membrane wraps the interior of the building that allows vapor, but not air to pass through. "It modulates permeability based on seasonal humidity to change the flow direction of the vapor drive," Johnston says. "This allows the wall construction to not trap vapor within the assembly and effectively makes the building air tight."
Performance Highlight: "The effective R-value of the Passive House wall assembly is 33.7, nearly 70% higher than the code minimum," Johnston says.
Stereoform Slab, Chicago
Detail: Optimized concrete framing
Firm: Skidmore, Owings & Merrill
Description: At the 2019 Chicago Architecture Biennial, the local office of SOM revealed its latest iteration of a more efficient concrete slab—“the most common element in contemporary construction,” according to the firm’s press release. The optimized arched geometry was created with reusable polystyrene molds fabricated with robotics, a faster process than erecting conventional wood formwork. “The built form,” says structural engineering director Benton Johnson, “is fluid in appearance and can be used in open-ceiling applications where additional cost and carbon footprint savings can be achieved.” Specifying low-carbon rebar and carbon-sequestering aggregate in the concrete could further reduce the project’s embodied carbon.
Performance Highlight: “This detail reduces concrete materials by 20% and steel reinforcing quantities by 10%, while increasing the span length of conventional flat-plate structures,” Johnson says.
This article appeared under the headline "Architectural Details to Reduce Embodied and Operational Carbon" in ARCHITECT's January 2020 issue.
