Conquering Carbon

Facade designs are key to meeting stringent New York City carbon reduction requirements
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Sponsored by the Ornamental Metal Institute of New York
By Barbara Horwitz-Bennett


While there are many measures that building owners can take to slim down their carbon profile such as switching to LED lighting or installing integrated control systems, many agree that facade improvements are key to achieving LL97 compliance, particularly with stricter requirements going into effect in 2030.

To put things into perspective, Bocra points out that 75 percent to 80 percent of New York’s large buildings should be able to meet 2024 carbon levels with relative ease, but before 2030, around 80 percent of these buildings will need significant retrofits and likely facade work.

“Facades are a key part of carbon deduction and energy efficiency reduction because they are, arguably, the most important part of a building’s energy efficiency strategy from a holistic standpoint,” explains Atilio Leveratto, vice president, CallisonRTKL, New York.

“Robust facades will lead to greater energy efficiency and less robust facades will lead to greater energy loss, all which have carbon implications,” agrees Mandyck.

Image courtesy of Lawrence Berkeley National Laboratory

Improved building facade designs can enable savings via reduced lighting consumption and HVAC equipment and loads.

In fact, air infiltration, heat loss, and solar gain through the facade account for up to 43 percent of a commercial building’s lighting, cooling, and heating loads.

“Improving facades is critical to compliance with LL97,” concurs Roberts. “Updating facade elements will keep buildings better insulated, making them more energy efficient. Technological upgrades to HVAC systems alone are not enough to ensure compliance, as those improvements must be supplemented by better-quality facades.”

Tied into daylighting/lighting and HVAC systems, the building’s level of air infiltration, heat loss and solar heat gain, will directly determine how much energy is required to heat, cool, ventilate, and light the interior. And this has significant ramifications on older New York buildings.

“The facades on most have been compromised in terms of maintaining a consistent thermal and air barrier. With the settling and structural movement that typically happens over time, exacerbated with extreme temperature fluctuations, as the permeability of a façade increases, air pathways are created,” explains Tommy Zakrzewski, PhD., director of integrative energy engineering, HKS Inc., Chicago.

“These air pathways, often cracks through building materials and individual construction components, increase undesirable infiltration. In many instances, infiltration can account for 30 percent to 50 percent of the heat lost or gained in structures that are not completely airtight.1 Furthermore, excess air leakage through the facade can also de-rate the effective R-value of insulation by up to 60 percent.2 Thus, the integrity of the facade plays a key role in meeting the aggressive emissions and carbon reductions in LL97,” he states.

In fact, the U.S. Department of Energy estimates that 40 percent to 50 percent of a building’s heating and cooling loads can be decreased by a high-performing enclosure. “Reducing these loads in turn has the compounding effect of downsizing mechanical equipment and lowers carbon emissions even further,” adds Woods. “These kinds of synergistic opportunities between the architecture and building systems are essential for achieving ambitious carbon reduction goals.”

Offering her perspective, Façade Tectonics Institute President Helen Sanders, Ph.D., expects that improving envelope performance in existing buildings—particularly those with old, single-glazed, non-thermally broken, leaky facades–will become an important strategy to achieving both the near-term 2024 targets and the longer-term 2030 targets.

In addition to improving efficiencies, a higher-performance building enclosure will boost occupant comfort, indoor environmental quality, and resiliency to better survive severe weather events.

Last year, New York City Mayor Bill de Balasio made a widely publicized statement that the city would introduce legislation to ban glass and steel skyscrapers in the fight against global warming, setting off a wave of backlash in the building community. In reality, LL97 does not seek to eliminate glass and steel facades. However, it does require them to meet a more stringent energy standard.

“With a high-performance building envelope, it is possible to create glass skyscrapers without compromising energy performance and still deliver the quality of space in terms of expansive views that developers want in order to market to tenants, and with sufficient daylighting and thermal and visual comfort to support a productive, healthy indoor environment,” says Sanders. “A win–win–win for the planet, the building owner and the occupants.”


As owners begin working to get their buildings up to par, architects, engineers, facade designers, and contractors will have a significant role to play in helping buildings meet these LL97 carbon reduction standards.

In terms of preparation, Stephen Selkowitz, affiliate, building technology and urban systems, Lawrence Berkeley National Laboratory, Berkeley, California, advises designers to start by deepening their understanding of the role that the facade plays in both energy impacts and occupant comfort/satisfaction. Then they should better familiarize themselves with the technological options available, and not just glazing, but shading and daylighting controls/management as well. “Some of the best available options are sometimes difficult to ferret out,” he explains.

Further, Bocra points out that there are some limitations to the U.S. Environmental Protection Agency portfolio manager’s tool which owners typically use to report to us in their annual energy benchmarking. Consequently, it is very helpful to engage with an architect or an engineer “to dig into the details of how they’re calculating their greenhouse gas emissions and fully understand where are the sources of the excess emissions in their buildings and then translate that into the opportunities that are going to help them move forward the fastest,” she says.

“To be in the best position to discover these ideal design solutions, this likely requires an integrated approach where a team of multi-disciplined professionals—with expertise in energy modeling, facade engineering, and thermal analysis—create a comprehensive delivery method that will see these projects through from start to finish,” adds Leveratto. “Having the ability to make decisions quickly about materials, thermal properties, modeling, and mockup will be key to finding the highest performing facade with the biggest impact to the building systems, while also taking into consideration the design aesthetic,” he explains.

Along these lines, Perkins and Will recently developed a new modeling tool called SPEED, Simulation Platform for Energy-Efficient Design. The tool was designed to significantly help reduce building energy use and carbon emissions at the earliest stages of design. While more suited for new construction, the tool will have relevance for many kinds of projects—once a new building receives its certificate of occupancy, it immediately falls under Local Law 97 requirements, so all New York City projects moving forward must consider carbon.

Image courtesy of Perkins and Will

Utilizing Perkins and Will’s Simulation Platform for Energy-Efficient Design (SPEED) program, the optimal combination of window-to-wall ratio and glazing type on the south facade of a New York City building is analyzed.

“SPEED gives design teams the power to rapidly model hundreds, even thousands of building scenarios—taking into account variations in sizing, massing, stacking, and orientation—to identify the highest-performing configurations,” explains Woods. “This includes configurations of the building envelope.”

Beyond carbon emissions and performance, Brandon Andow, PhD, RA, senior building performance analyst, EYP Architecture & Engineering, Denver, notes that the building facade is a “confluence of conflicting issues that span building physics and human comfort.” He further explains that heat transfer, water vapor transport, and advection are not easily intuited by designers and often defy rules-of-thumb.

For instance, designers may be looking to replace single-pane glass with double-pane insulated glazing, but if the non-thermally broken frames are left in place, the facade will still exhibit poor thermal performance and struggle with air infiltration.

“Architects and engineers will need to evolve their skill sets to effectively make decisions that increase the energy performance of facades and improve occupant comfort, all while avoiding moisture problems, navigating cost pressures, and reimagining one of the most recognizable skylines in the world,” says Andow.

Along these lines, some educational resources include courses offered by AIA New York’s Committee on the Environment and New York Passive House. Other groups offer spaces for professionals to exchange knowledge and ideas on facade retrofits and other elements of LL97 compliance. In particular, Max G. Wolf, AIA, P.E., CPHD, LEED AP, associate, SOM, recommends NYC’s Retrofit Accelerator, and the Building Energy Exchange, which hosts classes in Passive House design and THERM.

Personally, Wolf decided to become a Certified Passive House Designer and has spent time honing his skills in THERM, an LBNL 2D heat transfer modeling, and WUFI dynamic hygrothermal analysis. While professional modelers inevitably need to be brought in to perform these complex calculations, Wolf is now in a better position to work more effectively and efficiently with these consultants.

Mandyck further advises architects and engineers to transition from an energy to a carbon mindset. While these two metrics are sometimes used synonymously, they are very different things. For the most part, buildings do not emit carbon, they use energy, primarily in the form of electricity. That electricity may come from a fossil fuel electrical plant hundreds of miles away where carbon is emitted, but the building owner is now being held responsible for that.

“Before now, the playbook was all about energy, but now it is carbon. This is a big transition that we are going to have to make,” Mandyck explains.

He adds that as power plants become more renewable, this puts less pressure on the building design, so designers will need to pay more attention to the electrical grid.


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Originally published in Architectural Record
Originally published in November 2020