February 2006

By Ted Smalley Bowen

Frank Lloyd Wright's 1908 Unity Temple in Oak Park, Illinois is considered an early Modernist masterpiece for its compact monumentality and striking planar geometry. Although its interior ranks among the great public spaces of the 20th century, it proved uncomfortable almost from the start. An advanced but poorly executed heating scheme meant noisy radiators in colder months, and the lack of air conditioning and proper ventilation made the building a sauna in the summer.

Images: Courtesy Unity Temple Restoration Foundation

Last year the church's Unitarian Universalist congregation and the Unity Temple Restoration Foundation began the building's first major restoration, which is slated for completion in 2009, the centennial of the building's dedication. A significant component of the $12 million to $15 million project addresses the building's HVAC problems through the addition of a groundsource pump system for heating and cooling. The project will also involve repairs to the temple's reinforced concrete structure, refurbishing its interior woodwork, lighting and art glass windows, a new electrical system, and modifications for ADA compliance, including the installation of an elevator.

The project team, including Harboe Architects of Chicago and Architectural Consulting Engineers (ACE) of Oak Park, are working to balance the needs of the congregation with strict preservation requirements for the landmarked building, which comprises a temple, meeting hall, and entrance hall. "The original users are still using it. It has to function as a house of worship and as a tourist attraction," says principal Gunny Harboe. "It also happens to be an icon and one of most significant Wright sites in the world."

New HVAC efficiencies

In improving the building's indoor environment, the congregation opted for a system that would reduce operating costs and take less of a toll on the global environment.Ultimately, the design team developed a system of geothermal wells. The plan calls for a closed-loop fluid circulation system that will carry an antifreeze formula of glycol, ethanol or another environmentally benign substance. It also has provisions for an ice storage system for producing ice overnight to reduce the required chiller capacity, according to Mark Nussbaum, principal of ACE.

Nussbaum is still working out the number of wells and their exact depth , most likely 300 feet. But he says adding the water loop and ice storage capability does not add significantly to the cost of the project, given the system's greater efficiency and reduced chiller capacity.

The new HVAC system will mostly fit within the existing utility trenches and ducts at Unity, lessening the impact on the original structure.

In a bit of function following historic form, the scheme will be augmented by radiant heat, through the reuse of some of the radiators installed the year after Unity Temple opened.

Among Wright's innovations at Unity was a forced air heating system, fed originally by a coal-fired steam boiler. Poor performance led the congregation to add steam radiators after the first winter, according to Nussbaum.

"The main duct could've heated the whole building, but I don't think the distribution ducts were big enough. It was also hard to balance and manage the airflow," he says.

The boiler was converted to oil in the early 20th century and to natural gas by the 1970s, according to Nussbaum. A high efficiency natural gas boiler will replace the latter to provide backup heat and heat for cooking, he said.

The new scheme's demand/control ventilation system, which is triggered by carbon dioxide levels (which indicate the number of occupants), is tailored to the needs of both users and the historic building fabric, according to Nussbaum.

"It brings in only enough fresh air to meet actual needs, and it allows for a porous building," he says.

Unity's single-glazed leaded art glass is leaky and difficult to control thermally. But measures like storm glazing would compromise the building's aesthetics and could create moisture problems, according to the designers. Nussbaum says Unity's HVAC needs don't require an airtight building. "We don't have any delicate museum artifacts here," he says, "so we can improve indoor comfort without damaging the building's shell, which is pretty hearty."

ACE created software models of the building's energy performance, although its as-built conditions have never been fully documented. "It's difficult to do energy modeling for a building when we don't thoroughly know its construction," he says. "There are some voids in the masonry walls, for instance, but it's not clear exactly where they are."

But the models were accurate enough to approximate the building's performance with its present equipment and consumption levels. Overall, the calculations predict better efficiency during the heating season, which should compensate for the new cooling load. "We expect to see a 40 to 50 percent reduction of utility bills over what a conventional HVAC system costs," he says. Geothermal systems typically put out 80 percent less source emissions compared to systems powered by fossil fuels, he says.

Making the old new again

Wright's cast-in-place concrete structure was innovative for its time, and is still sound, despite some cracks and spalling, according to Harboe. "We're not anticipating replacing rebar," he says. "The major work was the overhangs," he says. Unity's signature heavy eaves were rebuilt several years ago.

The temple skylight requires significant restoration. "It's our intent to go back to the original design. There is some of the original fabric, but there's a question of how much we can reuse," says Harboe.

A photo dated 1925 shows a women’s group that may have been part of Unity’s early congregation.

Most of the temple sanctuary's oak trim is original and much of its original clear resin finish remains, according to Harboe. Wright applied color washes directly to the interior's plaster walls. These were subsequently covered under many coats of paint. The restoration team is looking to replicate the original washes.

Maintenance also figures in the restoration, as the designers consulted records of Unity's previous upkeep for clues to how building has changed over the years. They will also provide guidance on maintaining the newly refurbished building, according to Harboe.

One concern for the interior is that the planned changes, such as the new mechanical systems, air handlers and the like, might affect the temple's excellent acoustics.

The work is being reviewed by a team of architects, engineers, and preservation specialists, whose task is to anticipate the effects of any physical and aesthetic intrusions, and to verify that the new work is reversible where necessary. "We want to make sure we do no harm," Harboe says. "I think it's doable without any major gymnastics."