The most interesting work in an architect’s portfolio is not always the commissions they design for clients, but the homes they create for themselves. For Laura Blau and Paul Thompson, founders of BluPath Design and early adopters of the passive house movement in Philadelphia, that meant bringing their historic townhouse at 1722 Pine Street up to sustainable performance standards. Given the home’s original sources of energy were candles, wood-burning fireplaces, and coal, this was a major endeavor with myriad of challenges along the way.

The Pine Street project was completed in 2022 just short of reaching the ultimate goal of passive house certification. However, it was the first time the Philadelphia Historical Commission gave a thumbs up to retrofitting a property listed on the local historic register with passive systems.

BluPath Design previously completed a number of deeply sustainable projects prior to the construction industry’s adoption of energy-saving principles called “passive adjacent,” including a gut-rehab of their former home in Bella Vista. The U.S. Green Building Council’s LEED for Home Program was launched in 2008. “Passive adjacent is a viable alternative for homeowners who want to improve a property’s energy use, air quality, and water efficiency, but cannot meet passive house certification at the initial phase,” Thompson explained. In 2025, Thompson was the lead architect of a passive house project in Mendham Township, New Jersey. Blau is currently working on a passive house under construction in Bristol, Pennsylvania.

The duo’s townhouse at 1722 Pine Street was built in 1845 as a single-family home. In 1922, its first major renovation converted it into three apartments above a ground-floor professional office. When Blau bought it 30 years ago her first upgrade was turning the fourth floor deck into an inviting shaded space with a container garden.  

In 2016, Blau and Thompson eagerly embarked on renovating the entire building and relocated their home and architecture office there. Their plan included converting the first-floor offices to an owners’ bi-level apartment and office with upgrades and renovations in all units. Their to-do list included adding a fire sprinkler system, underpinning the basement, air sealing, and fully insulating the building, plus additional bathrooms and larger modern kitchens. They also needed to remove the gas service and convert it into an all-electric building with new mechanical, electrical, and plumbing systems.

1722 Pine Street was added to the Philadelphia Register of Historic Places in 1995, listed as a contributing property within the Rittenhouse-Fitler Historic District. In the beginning, the architects’ requests for alterations to 1722 Pine Street presented no problem for the Philadelphia Historic Commission. “Passive house performance required that we replace the historic single-pane double-hung windows at the front and the replacement double-hung windows at the rear,” said Blau. “We also wanted to add insulation with a stucco finish to the rear walls to protect the deteriorating structure and waterproof, insulate, and air-tight the porous brick face.” This is where the Historical Commission dug in its heels.

Attention was paid to preserving historic details throughout the process. “The Pine Street facade windows are trimmed with a thermal insulation milled to the historic profiles. They were not touched, other than new windows, light brick cleaning, star bolts, and historically designed first-floor shutters,” said Blau. “We preserved historic interior details such as restoring historic light fixtures and maintaining original wood floor, trim, and plaster walls wherever possible.”

While their Pine Street property was under construction, Blau and Thompson completed a passive house project in the Italian market which was the first PHIUS+ certified building in the region. “This was a totally new house, allowing for greater freedom in design than most retrofits. It was built on top of a former 7-Up soda warehouse for an Italian Market mercantile family,” said Blau. Locals do a double take at this 2,200 square foot, two-story dwelling with double-high windows and sculpted metal roof that provide both light and shade, along with winter warmth and summer coolness in a zero-energy house. The 90-foot-deep warehouse now provides a rare South Philly amenity, a garage, where the homeowner keeps his cars and kit airplanes.

After some negotiation, Blau and Thompson received permission to replace all of the windows with passive-house-simulated double hung units. However, approval to cover the rear brick took more convincing. They appealed the Historical Commission’s decision, using the Environmental Bill of Rights, which guarantees current and future Pennsylvanians the right to clean air and water. That’s a steep ask considering the 2025 American Lung Association report ranked Philadelphia among the worst in the nation for air pollution. “The difficulty in renovating a Philadelphia rowhouse for passive house certification is not the historical features, but the fact that it is a renovation of an old masonry building in a dense urban situation,” said Thompson. The front of their house faces busy Pine Street, part of the city where finding a parking space is a white knuckle endeavor at best, let alone unloading construction materials.

The architects’ renovation went into overtime. “We thought it would be a couple of years of construction. Not four or five,” said Thompson. “We went through multiple electricians, carpenters, and HVAC contractors whose work did not even meet code. The disruption was stressful.” As if this wasn’t enough, the City lost BluPath’s structural drawings and shut work down during the basement underpinning, costing the project another nine months. Due to these and other issues, the Pine Street house is not yet certified. “At this time we are over code, but not to passive house standard,” said Blau. “None the less, there is not another historic district property that has come as close to certification as ours.”

BluPath Design’s other projects included a Colonial-era house built in 1787 with an 1800s addition boasting the first in Society Hill to receive approval from the Philadelphia Historical Commission for a rooftop solar array. “The project was what we call a high-performance retrofit,” said Thompson. “Our work included improving the house’s layout, function, and coordinating high-performance building envelope and mechanical systems, while preserving the historic character inside and out.” Only from the mews along the side yard can you detect the presence of solar photovoltaic panels on the roof.

“When wildfires impact others, we have no stink or smoke because of our HEPA-filtered energy-recovering ventilation system works so well,” said Thompson. Passive houses typically lower external noise by 50 percent, while providing air quality usually found on mountain tops. “There is almost no dust so  I need my cleaning service half the time than I used to, and we no longer have mice!,” said Blau. For homeowners who suffer from allergies, this would be reason enough to invest in a retro-fit, if not a new passive house.

“We decided to convert our building to passive energy to be competitive in the rental market and to show that it can be done in an historic house,” said Blau. “We believe that it is imperative that renovations, especially of historic properties, should be done with long-term benefits in mind, using the latest building science knowledge, while maintaining the historic features that make Philadelphia such a wonderful place to live.”

While Blau and Thompson are aware of how the high cost of passive house conversions can affect people’s decisions, they remain optimistic about its future in Philadelphia.”We would love people to understand the long-term value in health, durability, and comfort passive strategies offer,” said Thompson. “There are thousands and thousands of rowhouses in Philly that need work. That work should all be to passive house performance, if not certification.”

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