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Harvard’s HouseZero Aims to Prove Retrofits Can Drive Energy Efficiency in Old Buildings

Energy efficiency and sustainability is foremost on the minds of many of the world’s great architects. From LEED-certified buildings to solar power, many designers and builders are working with ultra-efficiency in mind. But it’s not as easy to attack these challenges when working with buildings that were built many years ago.

That’s why a new project by the Harvard Center for Green Buildings and Cities (CGBC) is so exciting for many professionals within the architecture segment. The CGBC’s new venture is the “HouseZero” project, which is in the process of retrofitting a pre-1940s three-story home with green and sustainable technology. The timber-framed, cedar-lined building is located on a residential street near the Harvard University Graduate School of Design.

Wildly Ambitious Goals

To call the project ambitious would be an understatement. Most projects of this scope would start with a costly and often wasteful teardown—a process known as a “scrape“. Scrapes involve the purchase and demolition of an older home to make way for larger structures, and the practice has tracked the overall housing market.

Where HouseZero differs dramatically is in its approach. Instead of simply tearing down the structure and starting over with new construction, the team behind the project aims to transform a challenging building stock into a prototype for ultra-efficiency in existing builds via a complex retrofit.

The teams working with CGBC believe the retrofit potential of the current U.S. building stock has not been fully explored. That’s why the team is working in collaboration with Oslo-based international design firm Snøhetta and Swedish multinational construction and design company Skanska Technology, to retrofit a nearly 80-year-old building into a functional office for up to 30 researchers and staff. But the end result is really a byproduct of a groundbreaking process aimed to transform the home renovation market.

The performance targets for HouseZero are startling, including 100 percent natural ventilation, 100 percent daylight autonomy, nearly zero energy required for heating and cooling, and zero carbon emissions. In fact, the building will produce more energy over its lifetime than was used to renovate and operate it.

Groundbreaking Energy-Efficient Design

The design team’s approach to the transformation of HouseZero is fascinating. Rather than treating the house as a “sealed box”—the energy-efficient approach used by most green home designers when starting from scratch—the building envelope and materials that make up HouseZero are designed to interact with the seasons and the exterior environment in a more organic way. Just as people in colder climates take a layered approach to clothing, the house is meant to adjust itself both seasonally and day-to-day to reach its thermal comfort targets.

Naturally, the design and construction teams are fully replacing the HVAC system with an advanced system that relies on additions of thermal mass and radiant surfaces to help achieve the building’s ambitious energy goals. A geothermal heat pump will also be installed for peak conditions.

The plan for HouseZero also includes the installation of new flooring made of concrete with a high level of slag cement, which is a byproduct of iron blast furnaces. To make this unique product, molten slag diverted from an iron blast furnace is rapidly chilled, producing glassy granules that yield desired reactive characteristics when ground into traditional cement. Adding this high-density material to HouseZero will enhance the home’s thermal inertia, making it easier to manage dramatic temperature swings.

The plan for the retrofit also aims to reduce “hidden emissions” that are generated during a building’s construction and lifecycle. Measures are being taken to reduce gas emissions during fabrication, transport of building materials, construction, maintenance, and decommissioning.

Finally, the interior material palette is designed to complement the home’s original aesthetics, including natural clay plaster, Birchwood and nanoceramics—all chosen for their performance capabilities, local availability, and lack of gas emissions.

Of Air, and Light

Natural ventilation will be used to help adjust heating and cooling needs, using advanced materials to control fluctuations in humidity. The windows, skylights, and other features will be replaced to make daytime hours dependent on natural light and passive solar practices. Solar strategies will protect direct sun exposure during peak summer loading periods, taking in the maximum amount of indirect solar during all seasons.

On the east façade of HouseZero, the team will install a glazed solar chimney that uses sunlight to create thermal updraft. This feature helps draw hot air out of the building’s basement, which is being used as an event space.

An underfloor radiant system and ground-source heat pump adapted from ultra-efficient Nordic technology will add another layer to the home’s comfort control systems. Energy for the home will be generated via photovoltaic panels on the roof, while surplus energy will be fed back into the city power grid. Another solar thermal panel on the roof will supply hot water for occupants.

A Sustainable Solution for a Mass Market Challenge

“Before now, this level of efficiency could only be achieved in new construction,” said Ali Malkawi, professor of architectural technology at the Harvard Graduate School of Design and creator of the HouseZero project. “We want to demonstrate what’s possible, show how this can be replicated almost anywhere, and solve one of the world’s biggest energy problems—inefficient existing buildings. The long-term goal is to pioneer new energy-efficient solutions to be released into the market.”

Once complete, HouseZero will be a model for designers with its healthy indoor environment with natural light, pleasing acoustics, and zero carbon emissions, including embodied energy in materials. It will be a home-turned-office that is durable, flexible, functional, comfortable, and organically connected to its own natural environment. One might envy the researchers who will soon occupy HouseZero, a place for worker well-being, comfort, and productivity.

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