Philadelphia’s First Passive House Multi-Family Complex Ready for Occupancy

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After years in limbo, Philadelphia’s first multi-family Passive House housing project is finished and on the market. Located at 219-235 W. George St., the homes were developed by the Onion Flats group in association with Domani Developers. The housing complex is known as the Onion Flats Stable. Of the projected 70 units, the team later downsized the project to only 27 units due to financial difficulties.

The units have a net living area of 2500 square feet, which includes 3 bedrooms and office space, and 3 bathrooms. About one third of the units in this development are set to be Affordable Housing units. This housing project was designed to obtain the LEED Platinum status, making it the first multi apartment complex in the US to receive this certification.

This extremely energy efficient housing project is projected to generate 100 percent of its own power from a 4.23kW PV array. The exterior envelopes are super-insulated (R-34) with the aim of greatly reducing the cooling and heating costs and overall energy expenditure. The roof is comprised of multiple 8 inch deep intensive (occupiable) and 4 inch deep extensive (non-occupiable) Green Roof Systems. The green roofs increase each unit’s insulation values, while also fulfilling 100% of the Storm Water Management needs.

The installed 430,000 gallon tank will be used to siphon water from the high water table located in close to the neighborhood. It will also act as a geo-thermal “heat-exchanger” for the building’s central heating and cooling systems. The tank will also be used as a cistern for the rainwater collected on site. Such a multi-faceted water management system will reduce flooding in the surrounding area, bring down the heating and cooling costs and be used to irrigate the green roofs.

The units are fitted with triple-pane Intus windows and doors. These windows come in R values of up to 10 and offer options such as, wood/wood, wood/aluminum, U-PVC and aluminum. All operable windows made by Intus have three weather/air sealing points and multiple locking points making them very airtight. Other specifications of Intus windows are DP 70, a decibel rating (dB) 47, and Air Leakage of 0.01. Added together, the U-window values of the Intus windows range from 0.102 – 0.16, with the Passive House standard being 0.14. The Stable flats are also fitted with Intus doors, which have multiple locking points.

The building complex is also fitted with a 260 KW Photovoltaic Panel System, and has radiant floor heating embedded in polished concrete floors. The boiler for the radiant heating is centrally located and also heats the domestic hot water for all units. The apartments are also fitted with low-flow toilets, showerheads and faucets. The units are also equipped with a Smart Home Energy-monitoring system, allowing the future occupants to monitor their energy consumption.

The factory-built units are designed so as to consume up to 90 % less energy than traditionally built apartments. The entire housing complex was designed in the popular rowhouse style, which means it fits in nicely with the other buildings in the neighborhood. This building style was also the perfect model for modular manufacturing. The foundations of the Onion Flats Stable building were constructed on site, but the rest of the structure was factory built, which reduced the construction time by 50 %.

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  • Katy Hollbacher

    Tim & his Onion Flats team are really out there pushing boundaries–it is truly inspiring! Thanks for a great summary of this exemplary Passive House project.

  • Katy Hollbacher

    Tim & his Onion Flats team are really out there pushing boundaries–it is truly inspiring! Thanks for a great summary of this exemplary Passive House project.

  • Bruce A Johnson

    Thanks for the post this morning. I just happened to be in the Philadelphia area for a wedding this aft so went to check it out this AM. I was a bit disappointed only 3 were completed and not yet open for a tour, but was delighted with this positive development in sustainable urban living. Thanks again for sharing all this positive progress.

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