When Frank Lloyd Wright designed Unity Temple, he equipped the building with a forced air heating and ventilating system. A network of underground tunnels was construction to carry air from the basement on the south side of the building to Unity House and Unity Temple. Unfortunately, the system proved to be inaequate and was abandoned long ago. Since then, the tunnels have been used for piping, electrical, and communications cables. (Soon, the tunnels will have new life as an integral part of the new ground source heat pump ("geothermal") system that is proposed for Unity Temple.)
Most people don't know that there are tunnels under Unity Temple. They are set into the earth and are under the concrete floor slabs. You can enter the tunnels--and actually crawl through them--at several spots, but they are basically invisible to the naked eye. To make it more of a mystery, the one drawing we have of the tunnels from the time they were built, by Foster & Glidden Co., does not represent their true location.
As soon as we knew we were going to have to shore up the south roof, we knew that we would need to be really careful not to place the shoring posts on top of the tunnels. The weight of the roof bearing on a tunnel could cause collapse. Yesterday, Zera Construction called in Universal Construction Testing to locate the network of tunnels using ground-penetrating radar.
They were able to mark out the actual location of the tunnels. The diagonal blue lines show where the tunnels actually are:
Diagonal blue lines mark the location of Unity Temple's underground tunnels.
Safway, Zera Construction's shoring subcontractor, marked the floor with blue x's last week. As you can see, some of those x's fall directly in the path of a tunnel. Stay tuned for the solution.