By Jay Fox

Susie Clemens House is a modest three-story building located at the northern edge of suburban Philadelphia, in Hatfield, Pennsylvania. It provides 60 units of affordable housing for older individuals and is part of the larger Derstine Run campus, which currently consists of three buildings that contain 60 one-bedroom, one-bathroom apartments apiece.

Though the first building on the grassy, 28-acre Derstine Run campus opened its doors in 2011, the Susie Clemens House was not completed until 2021. The master plan for the campus indicates that a fourth building will eventually be built and that it will also provide more affordable housing for seniors. The buildings are operated by developer Advanced Living Communities, which currently manages six buildings and more than 500 units, and has served low-income seniors in southeastern Pennsylvania for over 50 years.

Despite its modesty, the Susie Clemens House is designed to Passive House standards. It received Phius+ 2015 certification in April 2022. The building’s exceptional performance is a reminder that Passive House buildings don’t have to wear their energy efficiency on their figurative sleeve. They can look like conventional buildings and still meet Passive House levels of performance and provide occupants with extremely cozy indoor spaces that are quiet, thermally comfortable, and supplied with a continuous supply of fresh and filtered air.

The modest finishes and simplified geometries of the Susie Clemens House also allowed the design team to reduce upfront costs, though it should be noted that state policy played a role in reducing costs, as well. When applying for federal incentives to build affordable housing within Pennsylvania, teams submit applications to the Pennsylvania Housing Finance Agency (PHFA).

Like other states, the agency uses a points system as part of a qualified allocation plan (QAP) to determine which teams receive the incentives. As of 2015, the PHFA added a criterion for Passive House certification, offering teams an additional ten points if they obtained certification. As the total number of possible points was 130 in 2015 and 150 in 2017 and 2018, deciding to seek certification during those years was considerably more valuable than at present (the total points allocated in the 2025/2026 QAP is 232).

As a result of this incentive, Pennsylvania saw an early surge in Passive House construction. The policy had the downstream effect of adding depth to the state’s pool of architects, consultants, builders, and tradespeople who are familiar with high-performance building techniques. With more experience and familiarity comes not only a better product, but also the ability to address and resolve difficulties more efficiently, explains Steven Winters Associates Principal Sustainability Consultant Scott Pusey. Pusey, a Certified Passive House Consultant, is also credited as being the Phius Certified Verifier on the Susie Clemens House.

Like many developers, Pusey says Advanced Living Communities recognized that Passive House certification would not only align with their mission to provide quality housing but also increase their chances of being awarded low-income housing tax credits (LIHTC) through PHFA. This turned out to be true, and the project was awarded the LIHTC in 2018.

Keep It Simple, Susie

The groundbreaking ceremony for Susie Clemens House occurred in 2019. Construction was scheduled to last 13-16 months, but the team had to pause during the height of the COVID-19 pandemic. It was completed in 2021.

The design schedule was even quicker, lasting only 4-6 months, and involved very few hiccups as architects KMA Design Studio worked with Pusey and the Steven Winter Associates team to make the building as comfortable and efficient as was feasible. One potential issue that the team recognized early on was the possibility of overheating. While the building may not be as dense as a high-rise in New York City or Philadelphia, the apartments are still relatively snug, and the combination of excessive internal heat gains combined with the hot and humid summers of Southeastern Pennsylvania was a cause for concern during design.

Luckily, the client’s vision for the campus involved situating the building on a north-south axis, so the solar orientation was already optimized. Additional modeling showed that exterior shading elements would not be necessary and that unwanted solar heat gains could be mitigated with conventional privacy blinds.

To further avoid thermal bridging, Pusey advised against the use of metal flashing around the windows and doors. To ensure no weak points in the enclosure, all glazing is triple pane. The windows come from Brooklyn-based IKON Windows. The team used their Optima Plus models, which have aluminum frames and are compatible with Passive House construction. The U-value for the fixed windows is 0.12, while the tilt and turn units have a U-value of 0.13. For their door systems and storefront windows, the team used fenestration systems from Kawneer.

The foundation is fairly conventional and not over-insulated, with an R-value of R-10. It is slab-on-grade with two layers of 1-inch XPS foam board insulation beneath. Pusey describes the two layers as being kind of shiplapped to avoid joints going directly into the ground. Along the perimeter is a CMU frost wall that has been outfitted with an aluminum cover.

The roof system consists of a Huber ZIP System roof deck that has an average R-value of R-43. As the majority of the roof is flat, it is topped with a white thermoplastic polyolefin (TPO) system. The roof houses some of the equipment for the building’s mechanical systems and is currently without a PV array. However, the roof is solar ready, and the owners anticipate installing a PV array in the future.

The mechanical systems are primarily electric (widespread adoption of electric DHW systems in multifamily construction was still a few years away when the team was designing Susie Clemens House). Each kitchen is outfitted with an electric oven and induction cooktop, and each unit is outfitted with a single-zone mini-split system manufactured by Samsung. Each unit has one air handler that Pusey describes as a “slim duct” that is concealed in the ceiling plenum, and then the refrigerant lines run up to the condenser unit on the roof. Each apartment is also outfitted with a Panasonic ERV that is also concealed in the ceiling.

While the units provide occupants with the ability to have more control over their personal space, there are two issues that arise when the HVAC system is this decentralized. The first concerns filter maintenance. The filters for both systems are accessed from within the unit through a drop ceiling. If they are not changed periodically, the result can be suboptimal performance. Pusey reports that the filters should be changed approximately three times per year, which can be a strain on maintenance crews, especially since they need to enter apartments in order to change out the filters.

Secondly, since each ERV needs to have independent ductwork for intake and exhaust, the result is a dramatic increase in the number of penetrations in the enclosure. While Passive House design principles typically discourage excessive penetrations, the impact on the building’s airtightness can be mitigated with methodical planning and the right tools to make sure the ductwork is sealed to avoid both air leakage and condensation around the ducts.

It’s not a complicated detail, Pusey notes. “There’s just a lot of them.”

Don’t Sweat the Small Stuff

To ensure all the assemblies were as airtight as they hoped, the team created mockups of wall sections on site that included details like the mansard roof and window installations and performed chamber tests. They then pretested some specific portions of the building once the enclosure was complete, particularly areas with the mansard roof, but didn’t break up the building into wings or floors before performing the whole building blower door test, which they passed on their first attempt. This is an especially monumental achievement because it was Harkins Builders’ first certified Passive House.

“It was one of the most professional construction teams I’ve worked with, and I’ve worked with a lot,” Pusey says. “It worked out because everyone on the team was very focused on achieving certification,” he adds.

Keeping the team on the same page involved working together early and onsite. This helped them maintain a set schedule, but it also kept the lines of communication open. Keeping the team focused on the overall goal is vital, and it’s best not to needle crew members about issues that may seem insignificant. “On larger buildings you can’t lose sleep over each and every one-off pinhole in the air barrier,” he says. “But you better make sure you catch the repeated gaps, cracks, and holes.”