Four Projects to Be Featured on PHN's Passive House Buildings Tour June 18

The Passive House Network 2022 Passive House for All Conference kicks off this week on June 10th with a day of remote sessions followed by an in-person event in Boston on June 17th. Virtual attendance is also available for those who can’t make it to Beantown next week. Combined, the event will feature 25 sessions, workshops, a manufacturers’ expo, and dozens of occasions to network and mingle.

Registered conference participants will also have the opportunity to take part in a Passive House Buildings Tour. The tour will depart from a site in downtown Boston at 8:30 am and include four stops before returning to the city by 5 pm. Lunch and transportation will be provided. The stops will include an office building, a school, a single-family dwelling, and a multifamily residence. To learn more about these projects, keep reading!

Office Building: Winthrop Center

When completed in early 2023, Winthrop Center will bring over 1.8 million gross square feet of residential, office, and retail space to Boston. At 691 feet, it will also be the tallest skyscraper in the Financial District and stand just blocks from the new 678-foot tower being built atop the city’s South Station complex. While the two may draw comparisons because of their heights, developer Millennium Partners Boston (MP Boston) anticipates that Winthrop Center will be recognized not only as a new peak along the city’s skyline, but as a beacon of building excellence and environmental sustainability.

The through-block area that makes up the ground floors of the Winthrop Center will serve as a public extension of nearby Winthrop Square and the surrounding urban landscape. Known as the Connector, this arcade will not only contain amenities for the building’s occupants, but also provide a home for year-round cultural programming and regular rotating educational, collaborative, and civic events. Rising above the Connector will be 812,000 square feet of Class A office space, along with 510,000 square feet of residential space housing 317 condos.

Certification from both the Passive House Institute and the International WELL Building Institute will be sought for the office space, which, if successful, will put the project on the path to being the largest Passive House office building in the world and the only project at this scale to achieve WELL Gold. While the residential portion of the project will be LEED Gold certified, the office component will be LEED Platinum certified. According to MP Boston, energy models indicate that other LEED Platinum buildings in Boston use 60% more energy than the office space in Winthrop Center is forecasted to, and a typical Class A building in Boston’s existing stock uses 150% more energy.

Since MP Boston began planning this project approximately six years ago, there has been a push to create what Brad Mahoney, director of sustainable development at MP Boston, describes as an exemplar of the next generation of buildings. Mahoney said that their starting point was to build in a way that aligned with the principles shared by people and organizations that view the climate crisis as an existential threat. Additionally, Mahoney said they wanted to create a building that could become a “talent magnet” in its own right.

Handel Architects, the project architect renowned for their social transformative and environmentally conscious design, advocated in the early design stages for integrating Passive House into the project. Handel and Steven Winters Associates, the energy consultants for Winthrop Center, had recently finished constructing the then-tallest Passive House building in the world—The House at Cornel Tech’s Roosevelt Island campus—and brought their expertise on the benefits of Passive House and how to apply it to the project. The team was joined by Suffolk Construction, which is managing construction services on the project. Additionally, MP Boston traveled to Germany and met with representatives from the Passive House Institute who provided guidance on the extremely ambitious project and agreed to use it as a pilot project.

MP Boston hopes that the success of the project will not only win them accolades from people who are interested in sustainability. They also hope to raise the bar for the entire industry.

“The climate crisis is here,” Mahoney says. “So how do you create leadership?”

Mahoney believes it’s by taking positions that challenge the wisdom of the status quo. Even if these decisions may at first seem quixotic, successful outcomes can push the market in directions that make what was business as usual just a few years ago seem archaic. “It’s a big undertaking, but it’s well worth it,” he says.

School: The Waring School

The Waring School is an independent school for students in grades 6-12 that sits just outside of the town of Beverly, a North Shore community about 20 miles northeast of Boston. Its campus has been located at the same bucolic site since 1976, when the school purchased an estate and inherited five separate structures: a main house, barn, farmhouse, greenhouse, and stable and carriage house. Over the years, these structures have been adapted for use by the school, but the stable and carriage house began to show signs that it was reaching the end of its lifecycle several years ago. Known around campus as “the School”, it sat within a floodplain and had been subjected to increasingly frequent floods that left the foundation and much of the original structure beyond rehabilitation.

It was clear that Waring needed a new School.

After reviewing several proposals, Waring decided to partner with OPAL Architecture, which is based in Belfast, Maine. OPAL had previously been the architecture half of the design/build company, GO Logic, and launched as an independent architecture firm in 2019.

As OPAL’s Management Partner Timothy Lock notes, one of the major challenges facing Passive House designers of high-occupancy buildings is overheating. “Once you get to a higher occupancy, trying to take advantage of direct solar gain is actually damaging to the energy model,” he says. “All the space-planning strategies we use for single-family [dwellings] are inverted,” he continues.

To counteract these solar gains, the team made use of an existing wooded area to provide shade to the building’s south-facing windows. “We used the design as a way to contort the building to ensure we’re getting shading where we need it and don’t have to count on the systems to do it for us,” Lock says. “The design should be able to do it on its own.”

They also designed the building so that the natural light comes in primarily from the north and east. This strategy influenced the location of the space for the All-School Meeting, which has been a staple of Waring’s routine and democratic spirit since its founding 50 years ago. By situating it in the northeastern corner of the building, the room is assured to get plenty of indirect natural light without running the risk of overheating. As part of the foundation insulation strategy, the team built a full frost wall, while the above-grade walls are comprised of an 8-inch wood stud wall and 6 inches of continuous insulation outside of the air tightness layer, thereby achieving an R-value of 52. The exterior is a Unilux window and curtain wall system that also includes some punched windows. The roof system has an average R-value of approximately 90 and is made up of wood trusses that are dense packed with cellulose and air sealed on the underside.

Thanks to its passive design, the building stays comfortable with appropriately sized active heating and cooling systems. When certified by the Passive House Institute later this year, the new School will be the first academic building in the state of Massachusetts to be recognized for this level of performance.

Learn more here.

Single-Family Dwelling: Park Passivhaus

Construction of what became known as Park Passivhaus began in 2012. Designed and constructed by Placetailor, the two-story house contains three bedrooms, no basement, an unconditioned garage outside of the building envelope, and a treated floor area of 1,317 square feet. The design is simple to avoid thermal bridging, with windows situated in the middle of the walls and installed in line with the insulation.

The foundation is an 8-inch reinforced concrete stem wall with a Stego wrap vapor barrier and an inner shallow ring beam that has been thermally separated by 2 inches of mineral wool, while the floor joists have been filled with dense packed cellulose that extends below the joists. The walls are double-stud construction, with 2x6 exterior walls and 2x4 interior walls that are filled with 14.5 inches of dense packed cellulose. The roof assembly consists of Huber Zip panels taped with Siga Wigluv black 60 and a prefabricated scissor truss insulated by 20 inches of loose packed cellulose. The vapor control and air barriers were both provided by Siga.

Homeowner and certified Passive House designer Vladimer Pezel says that this all resulted in some “pretty beefy” R-values. The R-value of the wall assembly is 56, while the R-values for the floor and roof are 61 and 76, respectively.

With respect to windows, the team opted for wood frame with aluminum cladding. In keeping with conventional Passive House construction, they are triple pane, tilt and turn. The door is also made of wood with a cork core and aluminum cladding. The windows and the door were manufactured by the Slovakian firm Makrowin and have U-values of 0.814 W/(m2K) and 0.754 W/(m2K), respectively. Surprisingly, Pezel says that the team found it relatively easy to obtain these components, because there was a distributor of high-performance fenestration systems already operating in the Boston area.

A solar thermal system located on the roof provides domestic hot water, while the heating and cooling come from a Mitsubishi mini-split heat pump system that consists of one condenser with a 22,000-Btu/hr capacity and two indoor evaporator units with a 9,000-Btu/hr capacity. Ventilation is provided by a Zehnder ComfoAir 350 HRV. To avoid overheating, Pezel has installed some shade sails over the patio door and the kitchen window, as well as some wooden slats to reduce the impact of the summer sun. Consequently, there are only a few weeks in August when it has been necessary to turn the AC on.

Some of the other benefits that Pezel has observed since moving into the home in April 2013 should be familiar to Passive House advocates. He notes that the walls and windows are never cold to the touch, even in the dead of winter. It’s also extremely quiet and likens it to being in a cocoon.

However, perhaps Pezel’s favorite benefit of living in a Passive House was realized after he installed a 4.8kW photovoltaic system on the roof in 2016 and made the house a net-positive building. Prior to this time, he says he paid between $60 and $80 per month for energy. Since installing the system, the utility company has been issuing him a credit, because the system pumps more energy into the grid than the family uses over the course of the year.

Learn more here.

Multifamily: The Loop at Mattapan Station

Preservation of Affordable Housing (POAH) and Nuestra Comunidad Development Corporation are working to transform a 2.57-acre parking lot next to the Massachusetts Bay Transportation Authority’s Mattapan Station into a mixed-use development that will include housing, retail, and community space. In addition to providing critically needed affordable and market-rate housing in the Mattapan community, which sits just south of Dorchester, the innovative transit-oriented development project will provide residents of the complex with a variety of transportation options, including public transit, ride-share, and bike-share, along with direct access to the Neponset River Greenway.

The site plan leverages local opportunities for growth and expansion by adding jobs, creating commercial space, and providing stable affordable and workforce housing. The plan calls for 135 rental apartments, half of which will be affordable for residents making 60% AMI and below, and approximately 10,000 square feet of first floor retail space. The design will highlight the Neponset River Greenway and create an access point for the neighborhood to this important community amenity.

By repurposing the 2.57-acre MBTA parking lot in Mattapan Square, Preservation of Affordable Housing and Nuestra Comunidad CDC will create a vibrant, mixed-income community that will strengthen the property’s connections and contributions to the surrounding community.

Learn more here.