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Case Studies: Making Housing And Mixed-Use Density More Affordable

There are a growing number of multifamily and mixed-use projects across the country using such strategies to tackle the challenges of density and affordability.

Affordable Housing in Portland, Maine

On the opposite coast, architect CWS Architects and general contractor Zachau Construction are adopting similar tactics in their affordable housing project, Wessex Woods. It’s a four-story, 40-unit, affordable senior housing development for Avesta Housing in the Nason’s Corner neighborhood of Portland, Maine.

By using mass timber, the team cut the hard costs related to long-drawn-out construction schedules.

“Traditionally it’s always been CMU (concrete masonry unit) for elevators and stairs,” said Ben Walter, president at CWS Architects. “But we were able to demonstrate that a new material, and a different set of details to install it, fit nicely here.”

They compressed the shaft’s expected three-week construction time to one day, reducing their budget by $75,000, while realizing additional cost savings related to lower labor, heating, and tenting requirements.

Drew Wing, chief operating officer at Zachau Construction, witnessed the project’s time-saving benefits of CLT and wood panel construction firsthand. “In addition to erecting stair towers and elevator shafts in a day, it also allowed the framing of the building to happen concurrently, something we could not have done with masonry,” said Wing. “We were also able to lift and crane the panelized components into place easily, saving an enormous amount of time on the project schedule overall.”

“The design team, construction manager, and owner all worked together. That's what allowed CLT to happen in this fashion,” Wing added.

Mixed-Use Infill Project in Atlanta

Infill housing and mixed-use development is a powerful way to bring more housing and amenities to community areas while enriching and blending with existing neighborhood culture and appearance.

The architects of the Emory Point project, a vibrant, mixed-use apartment complex in Atlanta, employed a number of strategies to create an affordable solution that also boosted density.

The property’s central location maximizes what they can do with the site. Its access to public transit ensures that residents can live comfortably without a car, reducing local traffic and carbon emissions, as well as the need for parking.

By building with wood—which allows for prefabrication off-site and quick construction—the developers met an aggressive schedule resulting in significant cost reductions for labor and construction.

“Cost for the structural frame portion of the building only was about $14 per square foot,” according to Brad Ellinwood, engineer on the project. “In comparison, a 7-inch post-tensioned concrete slab and frame would have cost $22 per square foot. So, the wood-framing option yielded about 35 percent savings in the structure.”

Building on Top: Innovative Use of Urban Space in Washington, D.C.

Another creative solution to space constraints and making the best use of urban sites is to build on top of already existing buildings—adding stories to established structures, allowing for higher density while retaining the economic value and historical significance of the original building footprint. Mass timber’s light weight opens new opportunities for overbuild construction. The 80 M Street addition in Washington, D.C., is creating additional office spaces, meeting areas, a beautiful rooftop terrace, and gathering places on top of an existing seven-story office building.

From Carbon Source To Carbon Sink: Redesigning The Built Environment For Climate Change

Amidst the urgent need for affordable housing and urban infrastructure, the culminating impacts of a changing climate demand dramatic shifts in how we design and construct our buildings. One important part of the solution—convert the built environment from a significant carbon source to a carbon sink.

The Urgent Need to Lower Building Carbon Footprints

Climate change demands dramatic shifts in how we design and construct our buildings. At the same time, the urgent need for housing and supportive infrastructure continues to surge at record rates. Buildings and their construction account for 39 percent of global carbon dioxide emissions, of which 28 percent come from operational carbon—the energy used to power, heat, and cool a building. Buildings’ operational carbon can be reduced through energy efficiency measures, and policymakers, architects, developers, and engineers have made significant advances in this arena. The remaining 11 percent of carbon emissions are generated from building materials and construction. This “embodied carbon” can account for half of the total carbon footprint over the lifetime of the building.

To reduce the greenhouse gas emissions associated with construction, specifiers and stakeholders need to act now to create embodied carbon strategies that reduce environmental impacts from buildings we’ll use well into the future. The costs of delaying any longer are too high. Greenhouse gas emissions have increased by 90 percent since 1970. A 1.5 percent increase in global warming will have catastrophic results for ecosystems and people around the world, including the United States.

Embodied carbon is a priority for many environmental, architecture, and urban planning organizations including C40 Cities, Architecture 2030, Urban Land Institute, and the World Green Building Council. Many experts believe addressing embodied carbon for buildings and building materials is critical to achieve the goals of the Intergovernmental Panel on Climate Change (IPCC) and the 2016 Paris Climate Agreement.

Embodied Carbon in a Building’s Life Cycle

Embodied carbon is determined by conducting a life cycle assessment (LCA) of a product, assembly, or the building over declared life cycle stages. An LCA study returns results for a number of environmental metrics, including the potential to impact climate, or “global warming potential (GWP)." Embodied carbon is the GWP result. Embodied carbon is measured for each stage of the product’s life cycle, allowing comparisons across any combination of stages.

As buildings become more energy efficient, the upfront embodied carbon from materials begins to account for a higher proportion of a building’s carbon footprint. Very soon, embodied carbon is likely to become the dominant source of building emissions.

Embodied carbon varies dramatically between concrete, steel, and wood, making product decisions key in achieving lower carbon buildings. Manufacturing wood products requires less total energy, and in particular less fossil fuel energy, than manufacturing most alternative materials including metals, concrete, or bricks.

Embedded Carbon in Wood Products

Embedded carbon is the storage of carbon for long periods of time. Wood products are approximately 50 percent carbon by dry weight. And wood’s lightweight advantage when it comes to density and city building is making it an attractive, climate-smart choice as pointed out in a research paper: “Lightweighting with Timber: An Opportunity for More Sustainable Urban Densification.” The use of wood products in buildings provides an additional environmental benefit by storing carbon removed from the atmosphere. This ability to sequester, or “embed," carbon makes wood an ideal product for buildings, which are designed for long service lives. Essentially, a wood building is a large carbon sink. This storage of carbon is a unique environmental attribute that does not exist in other structural products.

Photo courtesy of ThinkWood

Embedded carbon

Timber as a tactic for curbing climate change is backed by a growing body of research and advancements in calculating the carbon footprint of building materials. In a recent paper published in the journal Nature Sustainability, experts at the Potsdam Institute for Climate Impact Research in Germany delved into four possible scenarios of timber use in buildings over the next 30 years. In the first case, “business as usual,” 0.5 percent of buildings are made with wood while the vast majority remain constructed of concrete and steel. There’s a 10 percent timber building scenario, a 50 percent timber building scenario, and a fourth scenario in which the vast majority—90 percent of new construction—is made with wood. Their findings suggest that the lowest scenario could result in 10 million tons of carbon stored per year, and in the highest, nearly 700 million tons. “Buildings, which are designed to stay for decades,” researchers write in the paper, “are an overlooked opportunity for a long-term storage of carbon, because most widely used construction materials such as steel and concrete hardly store any carbon.”

While the research is limited to European wood construction, the authors of the study see global potential. “This is the first time that the carbon storage potential of wooden building construction has been evaluated on the European level, in different scenarios,” said Ali Amiri, one of the researchers of the study. “We hope that our model could be used as a road map to increase wooden construction.”

Case Studies: Carbon and Climate

Design professionals across the country and around the world are increasingly constructing buildings using light-frame and mass timber structures in a commitment to combat climate change. Not only does wood continue to store carbon, its insulative thermal properties lend well to energy efficient solutions like Passive House.