CGBC Headquarters: HouseZero


The Harvard Center for Green Buildings and Cities (CGBC) retrofitted its headquarters, a pre-1940s house in Cambridge, MA, into a first-of-its-kind test case to demonstrate unprecedented levels of building efficiency and promote substantial shifts in the design and operation of existing buildings. Dubbed “HouseZero,” the project aims to prove that ultra-efficient retrofits can, indeed, be achieved and replicated by coupling current technologies with better design. Targeting the most rigorous efficiency standards ever achieved by a retrofit, the building has the following performance goals:

  1. 1.  Almost zero energy required for heating and cooling
  2. 2. 100% natural ventilation
  3. 3. 100% daylight autonomy
  4. 4. Zero carbon emissions, including embodied energy in materials

All components of the building are sensor-ed to generate data that will allow the building to adjust itself and fuel CGBC research focused on actual data and simulated environments. The building also features a flexible, highly-controlled and monitored experimental lab that is hardwired to the building’s energy exchange system. Because the lab is connected to an ultra-efficient structure, this space allows for the testing, swapping, and optimization of new, intelligent technologies, façades, and materials to inspire the next generation of ultra-efficient buildings.


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HouseZero   HouseZero    HouseZero



This demonstration project attempts to address the global environmental challenge of climate change by focusing on inefficient existing buildings, which account for vast amounts of energy use and carbon pollution worldwide. In the United States, building stock is responsible for around 40% energy consumption—housing is typically 18-23% of that. While numerous new buildings have achieved net-zero or positive-energy performance goals, the retrofit potential of the current U.S. building stock has not been thoroughly explored.

As such, the CGBC intends to demonstrate that by coupling current technologies with better design, retrofits of our existing building stock can achieve rigorous energy efficiency goals. By retrofitting the current residential building stock in the United States to achieve even some of HouseZero’s radical efficiency standards, we can achieve significant energy savings, which will translate into billions of dollars in savings per year.

Some of HouseZero’s upgrades are solely required to transform the house into a functional office for up to 40 researchers and staff, but most enhancements to the existing house are viewed through the lens of the home renovation market. The CGBC believes that the best ideas should be transferable to other homeowners as a recipe for significant energy and carbon use improvements to their existing structures without costly or wasteful tear-downs. While a homeowner may not be able to implement every aspect of HouseZero, applying one or more of its components could positively impact its environment, the health of its occupants, and building operating costs.



HouseZero aims to rethink the conventions of building design and operation to fundamentally redefine how a home connects with and responds to its environment. Rather than approaching the house as a “sealed box,” the building envelope and materials of HouseZero are designed to interact with the seasons and the exterior environment in a more natural way. Much like a layered approach to clothing, the house is meant to adjust itself seasonally, and even daily, to reach thermal comfort targets.

The use of natural ventilation can substantially reduce energy use and improve thermal comfort. As such, several fundamental design decisions focused on our ability to harness this potential full-time. This presented a significant challenge as reliance on our external environment adds increased levels of uncertainty (while traditional HVAC systems allow us to reliably monitor temperature and air-flow). CGBC-driven advances in energy modeling allowed us to more accurately predict the natural ventilation potential of our local environment, which ultimately allowed our designers to make more informed decisions.

We fully replaced the HVAC system using a different paradigm which relies on additions of thermal mass and radiant surfaces throughout the house. A geothermal heat pump was installed for peak (extreme) conditions. Natural ventilation is used to adjust heating and cooling needs throughout the house as required and other materials will help to control fluctuations in humidity by naturally absorbing and releasing moisture in the air. Artificial lighting isn’t used during daylight hours because the design of the house is optimized to maximize daylight use and passive solar practices in each space. In other words, whenever daylight is available outside, natural daylight is provided inside the building. Solar strategies are employed to protect direct sun during peak summer loading periods, take in the maximum amount of indirect solar (all seasons) and allow direct winter sun to penetrate the interior of the house to a maximum depth.

With the goal of promoting lifelong efficiency, productivity and quality of life for occupants, the structure is designed to be durable, functional, flexible, and comfortable. It models a healthy indoor environment with natural light, pleasing acoustics, and zero off gassing materials. HouseZero also uses materials that are all typically low-impact, and recyclable wherever possible with extremely low life-cycle costs.