Reaching for Zero Energy in High Density Housing
Buildings contribute nearly 40% of greenhouse gases to the atmosphere, so the push is on to “get to zero” on many fronts. What happens when ambitious goals like zero energy meet a conventional building industry that’s structured on repetition and cost, in a market that struggles to keep up with massive demand? This is often—too often—our challenge.
But housing is a special building type. It defines how people live, determines access to vital services, even predicts the general health, welfare, and resilience of entire communities. Clearly, housing must be part of the solution to climate change, but carbon emissions directly related to a building’s design are only part of that picture. It isn’t easy for conventional sustainable design standards to accurately define what “good” looks like for any given housing project; the right priorities are inherently complex and site-specific.
The quest to get to zero poses a dilemma for housing. On the one hand, it sends a clear and compelling message about what we strive for: housing that stands on its own and is “part of the solution.” But if it dominates the conversation, zero-energy goals can also limit a design team’s ability to recognize strategies that may be equally or more impactful for a community and come at little or no cost.
A zero-energy building is most commonly understood to mean a highly energy-efficient building that generates as much energy as it uses on an annual basis, usually from on-site solar panels. The most obvious challenge with this housing concept is density. A strict “on-site” definition of zero runs counter to the goal of denser construction, which reduces transit emissions and displacement by adding more stories and creating more compact units. Although taller buildings use more energy overall relative to the room they have for solar panels, height tends to drive energy use intensity down, which is advantageous at a regional scale. (Energy use intensity, or EUI, is the total amount of energy used, over a year, per square foot of building.) Meanwhile, denser buildings typically increase EUI and make it harder to hit a zero energy target, because even though they provide more homes in the same amount of space, there are more refrigerators and televisions per square foot in more compact units. Hitting zero would mean making investments in more elaborate renewable technologies or off-site renewable sources, which may not be the most strategic use of resources.
Taller, denser buildings are also more carbon-intensive to build on a per-building basis. But many are likely a net win for the climate, as long as they are used as primary homes, keep people in their community, and are safe and healthy places. This does not minimize the ethical obligation of architects to work to reduce operational and embodied emissions on all projects, but the context of land use, planning, and equity matters.
When it comes to energy targets in our work, we want to focus on an efficiency target: the “lowest attainable” gross EUI for a dense, urban multifamily building. Loosely defined, this is an estimate based on what current technology can reasonably achieve, informed by the latest industry benchmark modeling for mid rise multifamily buildings.
The firm I work at, David Baker Architects, now has two completed projects that meet these “lowest attainable” energy benchmarks: Coliseum Place and Edwina Benner Plaza, both all-electric with significant solar production. The predicted EUI for Coliseum Place, a six-story, 59-unit affordable housing project just completed in Oakland, California, is 17 kbtu/sf-year, which falls to 9 kbtu/sf-year with on-site solar PV. While this might sound commendable, we will hold our applause. We’ve found that it is not uncommon for completed buildings to use as much as 20% to 50% more energy than predicted. Historically, some of this can be attributed to inaccurate initial modeling, combined with the use of cheap, natural gas to fuel hot-water systems. We also think this significant disparity is due in large part to a lack of testing, verification, and commissioning, which are puzzlingly uncommon in the multifamily sector.
Edwina Benner Plaza, our first all-electric building, with a predicted EUI of 15, has been occupied for three years and is operating nearly as predicted, at 16.7 kbtu/sf-year before accounting for PV. This success is most likely owed to a special focus on monitoring the building’s energy use and making sure its super-efficient heat pump hot-water system worked optimally. There are no other emerging technologies on this project. It is important to remember that for conventional multifamily housing, it’s still the little innovations that may offer the most powerful emissions reduction opportunities. This points us back to why pursuing “zero” may not be as much about new technologies and renewable energy solutions as it is about driving a change in process: a closer examination of the purpose and goals of climate-responsive housing.
FIVE WAYS WE CAN THINK DIFFERENTLY
1: Set clear goals.
The first step toward successful, climate-responsive multifamily housing is setting a set of clear, achievable goals, making sure they’re the right goals, and ensuring that they are backed up by a firm commitment. The goal should be the answer to this question: What would it look like for this project to “stand on its own” and be “part of the climate solution”? Energy accountability is certainly a part of the answer, and the goal should probably include a target EUI and as much PV as the owner can possibly afford. But the goals must be a natural fit for the strengths and vulnerabilities confronting a specific community.
2: Evaluate value with cost.
The next step is to use design tools that allow the team to evaluate design options on the basis of value—a measure’s ability to serve the goals of the project—rather than cost and compliance by themselves. Cost and basic compliance dominate as decision-making factors without having a clear purpose that extends beyond providing “four walls and a roof.” For example, comfort models and resilience- planning rubrics are two tools we use to track predicted outcomes of the decisions we make.
3: Connect value to social equity.
How the team defines “value” should be based on an examination of residents’ improved access to opportunity and be mindful of the complicated relationship between social equity and technological innovation.
Coliseum Place taught us that energy efficiency was actually the least-important selection criterion for residential heating, cooling, and ventilation systems. Because HVAC system options are limited and bring enormous cost implications, resident health, comfort, resilience, and sense of dignity and control must take precedence. The good news is that you usually don’t have to trade efficiency for human benefits. But the attitude and the approach matter. This logic should extend to all areas of design if we recognize all the ways in which the design of our homes and neighborhoods impacts our quality of life. The more that residents have to cope with a home that is isolating, unhealthy, or unsafe—or that becomes unsafe in a disruptive event—the harder it will be to reduce the overall, long-term footprint of housing.
To successfully reduce emissions in multifamily housing, we should strive to give people of all incomes and abilities equal and fair access to technologies that allow them to adapt and thrive in a changing world. The pandemic has thrown this imbalance of access into high relief. It also highlights a relatively cheap measure that might seem far outside the scope of a zero energy discussion, such as high-speed internet and virtual mobility. Many low-income households lack access to this essential service, which, pandemic or not, limits the community’s ability to thrive. Buildings can’t solve systemic inequities, but this represents the kind of blind spot we can have when global, greenhouse gas–reduction goals define how we think about sustainable housing.
4: Remember carbon!
It’s important to remember that zero-energy buildings can have very different carbon-reduction profiles because they still use grid electricity, even though they contribute to an overall greener grid. Strategies to load shift and add storage can not only deepen future emissions reduction, but also save the owner utility costs and contribute to community resilience. You can do these things without “getting to zero.”
Embodied emissions are another critical factor. Coliseum Place taught us that, while we might assume there is not much room to reduce embodied emissions in a typical multifamily building, we can’t forget to have a conversation about our options. For a wood-framed building with one level of concrete, our structural engineer, KPFF, told us that reducing the emissions of the concrete foundation alone by replacing as much cement as we could get away with, using lower-carbon alternatives, would save about 175 metric tons of CO2, which happened to be the very same reduction our zero energy measures would achieve by 2030, based on a crude, back-of-the-envelope estimation.
5: Commit to verification and training.
The last and most important change to our process is not new, but, again, puzzlingly new to this sector: verification. This would include basic but thorough examinations of things like envelope-framing efficiency, insulation installation and air tightness, efficient hot water distribution, and systems commissioning. It may extend to pre-programming thermostats and giving residents clear information about the systems in their apartments. The cost of this work is minor within the context of large systems decisions, and setting the tone influences everything from more effective pre-construction meetings to successful handoffs with building operators and residents. If Coliseum Place meets its ambitious EUI goals, for example, it will be because residents understand their comfort systems,and the distributed hot water system works as intended, which relies on thoughtful and intentional communication with the building manager about the design.
We have many immediate changes to make and more to strive for in the coming years. To draw down emissions and begin to reverse global warming, we have to rethink how we work on every project starting now. Part of that is recognizing that climate-responsive design is not about meeting singular, absolute goals like zero energy. The power of housing providers to fight climate change starts locally, in securing and expanding direct benefit (stability, health, adaptation) to the communities where they operate. This calls us to find a broader understanding about what “zero” energy (and carbon) means for housing.
Featured image: Edwina Benner Plaza was completed in Sunnyvale, California in 2019. Photo by Bruce Damonte.