A 100-plus-year-old brick rowhouse in Lancaster, Pennsylvania, has been retrofitted to meet Passive House certification, a performance standard that requires very low energy use and an extremely airtight building envelope, verified through testing rather than a simple checklist. The project took more than two years and combined layered air sealing (a fluid-applied membrane on the masonry, tapes and sealants, and an interior air-vapor barrier), three kinds of insulation, and triple-pane windows. The finished home tested at 0.3 ACH50 (air changes per hour at 50 pascals, a measure of leakiness), well under the Passive House limit of 0.6.
Heating and cooling for the whole house comes from a single two-ton heat pump system with three indoor units feeding different zones, chosen because it could still heat effectively down to -15°F. Because the house is sealed so tightly, it also needed a dedicated ventilation system, an energy recovery ventilator (ERV), which brings in fresh outdoor air, recovers heat or coolness from the air being exhausted, and distributes it through the house. Bathrooms, the kitchen, and a wellness room with a steam shower and sauna are vented separately to manage moisture. A heat-pump water heater and heat-pump clothes dryer round out the system, and solar panels are expected to bring the home close to net-zero energy use.
The project shows that even a historic home with limited space and shared walls can reach very high efficiency standards, though it required unusually close coordination between the builder, HVAC contractor, and outside verifiers from the earliest planning stages.
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