In Philadelphia’s Northern Liberties neighborhood, where narrow rowhouses shape the urban fabric, architect Lauren Thomsen is charting a path toward a more sustainable model of city living. Her namesake practice, Lauren Thomsen Design, is an architecture and interiors firm dedicated to passive house construction and high-performance design.
Passive architecture relies on rigorous standards of insulation, airtightness, and energy modeling to drastically reduce a home’s energy consumption while maintaining year-round comfort. For Thomsen, this technical precision is paired with a restrained, modern aesthetic that emphasizes quality, efficiency, and longevity.
The Northern Liberties Passive Rowhouse is the perfect example. Certified under the PHIUS+ 2018 standard, the home creates bright, expansive interiors on an 800-square-foot lot by prioritizing openness, connection to daylight and durable natural materials. The result is a fresh take on the Philadelphia rowhouse tradition, proving that smaller, smarter spaces can provide greater comfort and livability.
Thomsen, an award-winning architect, educator, and member of the Carpenters’ Company, sees passive design as both a responsibility and an opportunity. Her projects challenge conventional ideas about square footage and style, instead emphasizing environmental performance and spatial experience.
In conversation with DNN, Thomsen reflects on how teaching has shaped her design philosophy, the strategies behind her celebrated rowhouse, and the promise of passive architecture as it gains ground in the United States.
Teaching passive architecture
DNN: First, let’s begin with a bit of your background. You’ve taught at Temple, Jefferson, and RPI, and are part of the Carpenters’ Company. How has teaching shaped or changed how you design?
LT: Being in a teaching environment is incredible because students have an indomitable energy that they bring to the design process. In the academic world, one is not mired down by the realities of executing a project. Students, therefore, have the opportunity and are encouraged to dream big with design possibilities. It is incredibly invigorating and a good reminder that one can push the envelope, even in practice on real project work.
DNN: What first drew you to sustainable architecture and eventually to the rigor of passive architecture and high-performance design?
LT: What we as architects produce has a lasting impact on the built environment and on those who inhabit our projects. I believe architects have a responsibility to design solutions that do as little harm as possible, or even benefit the ecosystems with which they interact.
The Northern Liberties Passive Rowhouse
DNN: On a narrow Philadelphia lot, you managed to create interiors that feel calm and expansive. What design strategies made that possible?
LT: The clients wanted a minimal approach in terms of space, amenities, and materiality, and also wanted the project to be as high-performance and resilient as possible. We kept the interiors open and bright and used a minimal material palette.
DNN: You gave up interior square footage to open the home to the adjacent park. Why was that decision worth it? Since the home buyer has been taught to maximize square footage, make the argument for a homeowner on the fence about doing something similar.
LT: The decision sacrificed precious potential interior living space on the tiny 800 sf lot, but allowed for glazing on the long southern axis with southern exposure (uncommon for rowhouses), created a visual connection to the park, and also provided an opportunity for a small terrace off the main living space. Increased natural daylight, views to the park, and the ability to step outside from the main living space are daily benefits for the homeowners. Sometimes, the experience of the space is not weighed into the design decision-making, but we really stress this in our office. In this case, less was more.
DNN: The Passive House nods to the rowhouse tradition but there’s also something new and fresh about it. What do you love about classic row houses and what sort of updated spin do Lauren Thomsen designed row houses have?
LT: We tend toward a minimalist yet warm aesthetic, open planning that focuses on access to daylight and views wherever possible. Many rowhouses feel dark and cramped as a result of the narrow lots and solid party walls. To us, there is an honesty in designing for light and space rather than adhering to a specific design style or period.
DNN: Talk to me about the materials you used in the Passive House. How do you weigh durability, sustainability, craft and creativity in material choices?
LT: We used natural and durable materials wherever possible on both the exterior and interior of the project. On the exterior, resilient corrugated metal is paired with thermally modified tongue and groove red oak siding, which is more durable than regular red oak siding. We keep it honest and smart.
DNN: What was the most technically demanding aspect of achieving PHIUS+ 2018 certification, and what did you learn that might shape future projects? Were there any surprises/unexpected hurdles?
LT: From a performance perspective, designing and constructing a single-family passive house in an attached and dense urban condition was challenging. The team actually worked with PHIUS to modify their certification standards to better account for adiabatic party walls in the envelopes of attached single-family homes and pave the way for other project teams with similar design ambitions.
DNN: The Passive Home integrates EV charging, battery storage, and smart panels. How do you ensure technology feels like part of the architecture rather than a mechanical add-on?
LT: We put them in the garage! (Just kidding). In reality, we work as hard as possible to reduce the home’s energy load before considering energy generation and storage. From the outset, we work iteratively with energy modeling to refine the design to be as efficient as possible. Once we’ve ‘maxed’ out the benefit of added efficiency, we move toward these technologies.
Industry & cultural context
DNN: How do you respond to concerns that energy performance standards might constrain design, and instead ensure they enrich the quality and feel of the space?
LT: There are unsung benefits to high-performance homes, particularly in urban conditions. Perhaps the most important of those is the acoustic privacy that a highly insulated envelope and high-performance windows can bring. Being transparent, the most significant constraint is not spatial, but rather that of cost.
DNN: Adoption & Scaling – Passive House is still niche in the U.S. compared to Europe. What do you see as the biggest barriers to adoption, and is that changing?
LT: As mentioned above, it is an issue of cost, both to build and to certify. The certification process is evolving to be able to include more projects and we are excited to see that happen in the coming years.
Collaborating on passive design
DNN: Where do you see the most powerful opportunities for collaboration between architects, interior designers, and makers, and how must architectural education evolve to foster that?
LT: Since the pandemic, our homes are increasingly important spaces in our lives, and the average individual is spending more time thinking about the spaces they spend time in. This is exciting for our industry.
Our goal would be to educate individuals as to the benefit of good design and encourage them to make changes, whether design or performance related (preferably both!). This naturally will require collaboration and present opportunities for cross-pollination of industries, and designers should be open to that.
