Shadyside Passive House
The Victorian house in the Shadyside neighborhood of Pittsburgh, Pennsylvania, had been re-muddled several times and was in dilapidated condition. Thoughtful Balance (TB), a Pittsburgh-based architecture firm specializing in sustainable, low-energy design, decided to take a chance on the gut renovation of the 100-plus-year-old, 3,000 ft2 home. Ten years earlier, TB had completed another gut renovation project right next door; this was essentially the same house.
As the owner of TB, I wanted to design to Passive House (PH) standards and also wanted to make it possible to compare utility bills for this house with utility bills for the code-built house next door. (Details of the two houses are shown in Figure 1.) Measured performance from previous PH projects indicated that by designing to PH standards, she could save 70% of the energy used by the code-built house. As strong believers in PH design, and in its ability to provide a comfortable, energy-efficient environment, TB was anxious to bring the first PH retrofit to this part of Pittsburgh, and to create the neighborhood’s greenest house.
Passive House Details
The PH method of building design was first developed in Germany in the early 1990s. Since then it has become popular throughout Europe and is rapidly being adopted in the United States. Architects here have completed a variety of PH projects at little or no additional construction cost. PH design focuses on energy conservation and efficiency; a U.S. house built to PH standards saves about 65% of the energy consumed by a comparable code-built house.
Figure 1. Details: Passive House vs. code-built house
Figure 2. Energy use: Passive House vs. code-built house
Figure 3. Money saved: Passive House vs. code-built house
In Europe, PH has a proven record of cutting energy use by as much as 75–80%—or more than most LEED buildings. PH design makes it possible to conserve financial and natural resources while providing unmatched interior comfort and healthy air quality—all without costly and complicated equipment. It is a performance-based designation (as opposed to LEED’s point-based designation) and can be applied to existing buildings as well as to new construction. Two performance targets for PH are an annual heating-and-cooling source energy consumption of 4.75 kBtu per square foot, and an envelope airtightness of 0.6 ACH50.
Passive House focuses on the building envelope rather than on the mechanical systems. Using energy modeling, designers superinsulate the envelope and then ventilate with fresh air. Solar orientation can be optimized for controlled solar heat gain and shading as needed. Constant ventilation maintains fresh interior air, and reduces the size of the mechanical system to a fraction of that of conventional systems. The result is a space that is energy efficient, comfortable, and healthy. PH-designed buildings use minimal energy for heating and cooling, allowing owners to decrease their ecological footprint.
For the house in Shadyside, none of the original details was intact, and the façade had reduced openings and aluminum siding. After gutting the interior and stripping the siding, TB installed a layer of outsulation, in addition to filling the walls with dense-packed fiberglass. The resulting insulation levels were R-53 for the walls and R-83 for the roof. All the ducts were sealed at the joints to prevent air leaks. Solitex Mento membrane was used as an air barrier over layers of taped Poli-Iso foam board. Triple-pane glazing in thermally broken window frames was installed throughout the house for maximum energy efficiency and extended life span.
The basement was excavated, the slab removed, and a new one poured, in order to insulate, damp-proof, and create head height for usable space. The basement insulation levels included R-33 for the basement walls, and R-21 under the slab. Now the basement conditioned space is as comfortable as the rooms upstairs.
The Passive House retrofit obtained an airtightness rating of 1.5 ACH50. An airtightness rating below 4.0 ACH50 is ideal for new construction, so achieving that rating in a house over 100 years old is truly remarkable. The airtight shell allowed for significantly smaller mechanical systems, housed in a corner of the basement. A high-efficiency heat pump uses less energy than a standard system, and an energy recovery ventilator swaps stale indoor air with fresh outdoor air. The predicted annual source energy consumption for the house is 5.93 kBtu per square foot for heating and cooling.
From the outside, the house fits seamlessly into its Victorian context. Inside, the floor plan was opened up to create a contemporary feeling, with double-height spaces and a wall that opens up to the garden outside. Walnut book-matched cabinets, maple hardwood floors, white quartz countertops, open stairs, and recessed LED lighting let the rich materials and quality of the house be expressed with simple clean lines. Oversized wood doors give the house a solid yet intimate feeling.
Renovating the house to PH standards cost 10% more than a traditional renovation of the property would have cost. However, heating and cooling the retrofitted space is estimated at less than $35 per month, with a projected energy savings of $80,000 over 30 years.
Though the project has not yet tracked a full year’s worth of energy consumption data, the performance comparison between the PH retrofit and the identically sized, code-built house next door shows how quickly those energy savings will add up. Over a five-month period beginning in October 2015, the PH retrofit used a total of 4,674 kWh, while the code-built house used 30,192 kWh. This translates to a savings in energy of 84.5% (see Figure 2). Energy costs for the PH retrofit were $691, versus $1,850 for the code-built house. This translates to a savings in money of 62.6% (see Figure 3).
In addition to saving energy and money, a PH is noticeably quieter, due to its airtight shell and superinsulation. This became a selling feature for the house in Shadyside. With no drafts or cold spots, a PH is also more comfortable in winter—again, a selling point for the Pittsburgh house. Zoned heating systems keep temperatures even throughout the building, and the air in a PH is frequently described as sweet. The ventilation system ensures a complete change of air every three hours, making the house a very healthy, comfortable place to live.
Realtors advised the owners that appraising the retrofitted house was going to be a challenge, as the house was priced well above average for the neighborhood. Two appraisals were completed that upheld the increased value for a home designed to meet PH standards, due in part to the projected energy savings of $80,000 over 30 years. This project set a precedent in the city for establishing the value added in building a Passive House.
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