Past + Present = Future

Early 20th century history meets a sustainable future in this energy-efficient renovated home.

When they considered the idea of a housing remodel, owners of the Passive House Institute U.S. (PHIUS) ZERO Historic Renovation project in Oak Park, Illinois, had a simple thought: They wanted “a house of the future inside a house of the past.”

From the Judges “This project is an excellent example of a deep energy retrofit that preserves the historic character of the home while updating the building envelope and mechanical systems.”

That future home, as envisioned by the owners, was to make the kitchen an important central gathering point without compromising workspace or visually taking over the interior. Home office spaces and a gym were requested. There was to be a “strong connection” to the backyard for family activities. And the house was to be an all-electric house with low baseline energy consumption, solar panels, and backup power. 

The homeowners got their wish: Their 3,568-square-foot project is a PHIUS Source Zero pre-certified retrofit of a 1902 house in an Oak Park Historic District. Bringing the house in line with modern ideas about space, energy, technology, and health effectively meant a gut renovation, something that Bosi Construction Company and Tom Bassett-Dilley Architects (TBDA) completed in December 2023. 

“Our mission is to help build a clean energy future, and scaling up decarbonization is one of our main strategies,” says TBDA architect and owner Tom Bassett-Dilley. “Clients find us and ask for this kind of project. We wanted to prove that even an old house can meet historic preservation criteria while meeting and exceeding 21st century goals for quality, energy efficiency, and resilience. We believe that this proof-of-concept project can inform many other future retrofits.”

TBDA also believes that this kind of thinking is a key strategy for the best, fastest path to net zero emissions by 2050, radically reducing energy use of old buildings. Only a modest upfront embodied energy input is needed in communities like Oak Park, where the greatest share of greenhouse gas emissions comes from heating old, leaky buildings. Tearing down and building new is not a viable strategy, as it requires huge amounts of upfront embodied energy in materials, while throwing away the old material.

The company notes that unlike cars, whose shape and construction materials have modernized significantly from the early 20th century, most homes are still constructed with a concrete foundation, wood framing, and brick and stucco cladding. This home’s overall mass, window area, and orientation are passive in nature since the home was built before large mechanical systems were a viable option. 

As a result, significant changes were required to bring the home into the 21st century.

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Reimagining the Back of the House

Homes of the early 1900s typically treated the back of the house as a “service” area, with minimal openings and little storage. Outdoor space was focused on the front porch, which was most likely the main entrance. With more frequent car use, more stuff needing a place (mudroom), gardening, and outdoor grilling and playing, the back entrance needed a whole different expression—including some architectural love, like the rest of the house. 

The back entry was reconstructed on-grade with a sheltered patio outside. The ceiling height now matches the main first level, so there are impressive sight lines from the kitchen out and down to the patio and backyard. Meanwhile, the big roof shades the east-facing windows while making a strong outdoor space.

Insulation, Where Art Thou?

This was an eye-opener, according to TBDA: The old house didn’t have any insulation, period. The necessary retrofit included all surfaces of the thermal envelope, as continuously as possible.

This required redoing the basement slab, which enabled a capillary break/vapor barrier, passive radon system, and insulation at the bottom of the house. These steps are needed to ensure a healthy interior.

“We used just enough HFO-blown closed cell foam to protect against condensation risk, and filled the rest with cellulose,” Basett-Dilley notes. “To get the optimal insulation level, we framed a new wall a few inches to the interior, which let us create level, square, and smooth interior surfaces.”

Airtight vs. Leaky: No Contest

Given that the original house was built before the membranes, tapes, and sealants that exist now, it was no surprise that the house leaked like a sieve, TBDA notes. The insulation strategy needed to align with an airtightness strategy that accounts for all penetrations—such as windows and exhaust vents—and connects between surfaces (slab, foundation, framed walls, and roof). 

Following window installation and slab and insulation work, TBDA used a non-toxic aerosolized compound that filled all the gaps as the house is pressurized with a blower door during installation. This typically isn’t needed on new construction but can be a godsend on old buildings with complex geometry, TBDA notes.

Troubleshooting lack of airtightness on such an old house proved to be a construction lesson. “It can take multiple passes at blower door testing and sealing,” Bassett-Dilley notes. “The cramped and complex roof/wall intersection prevented easy access, requiring multiple attempts.”

Goodbye to Natural Gas 

As a decarbonization project, TBDA approached PHIUS Zero like its other retrofits: It dropped reliance on natural gas, opting instead to use ground-source geothermal heat pumps for heating, cooling, water heating, and the clothes dryer, and switching to induction for the cooktop. 

Accommodating enough solar photovoltaics (PV) within historical guidelines to offset the house energy proved to be a challenge. To keep the house roof visually intact, solar PV was installed on the east- and west-facing gabled garage roof (per the town’s Historic Preservation Commission requirements), with a small additional array on the addition’s low-slope roof. 

“We were surprised how resistant the Historic Preservation Commission was to our initial proposal for a solar PV-covered new garage facing the street,” Bassett-Dilley notes. “In light of that opposition, we rotated the garage so the panels were not as visible from the street. It cost us about 15 percent efficiency but allowed the project to move ahead.”

A backup battery system allows for resilience in the event of power outages by supplying critical circuits while being fed from the solar array. 

The installation was so successful that the home’s energy bills are near zero. The home is also healthier, according to TBDA. “Cooking and line leaks inside the home have been shown to be significant pollutants, often making homes more toxic than the outdoors,” Bassett-Dilley notes. “The big-picture energy future is that electrification plus renewables equals zero emissions—it’s where we need to go.”

Ground-Source Heating Plus ERV System

Older homes use a lot of coal or gas to heat their uninsulated, leaky shells. TBDA’s model is the reverse of that, insulating and tightening enough that only a small amount of energy is needed to maintain comfort.

Ground-source heating is more efficient than air-source, but tends to require a single ducted system, versus smaller distributed systems common with air-source. And because all tight houses need good ventilation, TBDA uses balanced energy recovery ventilation (ERV) systems to extract pollutants from areas such as the kitchen, baths, laundry, workshops—even cat litter boxes—and provide equal fresh air to bedrooms and living spaces.

About 80 percent of the energy of the outgoing air is transferred to the incoming air, so it’s an efficient way to maintain healthy, filtered air, TBDA notes. MERV 13 and higher filters can even remove significant amounts of pollutants like PM2.5, the culprit in skies tainted by wildfires in summer. 

“This project had exemplary communication between owner, builder, and architect, so there were no ‘lessons learned’ resulting from lack of coordination or miscommunication,” Bassett-Dilley says. “The entire team is proud to have tackled this challenging project and proved that even an old house can meet historic preservation criteria while meeting and exceeding 21st century goals for quality, energy efficiency, and resilience.” 

To keep the house roof visually intact, solar panels were installed on the east- and west-facing gabled garage roof.

PHIUS ZERO makes extensive use of natural lighting and energy-efficient LED downlighting.

Stairway bannisters and walls throughout the home feature no-VOC paints.

Project Stats