This is where it all begins, mess up here and it sends ripples of catastrophe spending upward throughout the rest of the construction project, even more so since we were building the walls from SIP panels which don’t lend themselves to on site modification like can be done with traditional framing. Quite simply the function of the footers and foundation is to anchor the house to its location and support the weight of the house. In climates where freezing occurs it most also be designed to prevent “frost heaving”. Living in Park City, we are no strangers to cold and freezing weather, and local codes dictate that the footers be buried 36 inches below grade. There is another way to prevent frost heaves that gets around excavating the footers so deep. It called shallow depth frost free footer design first popularized by the famous American architect Frank Lloyd Wright in the 1930’s. It uses “wing” insulation around the outside perimeter of the footers. The theory is that as heat escapes from under the house it spreads outward. By putting 4 X 8 foot sheets of 2 inch EPS (expanded polystyrene better known as Styrofoam) around the outside perimeter of the footers, the heat is trapped closer to the footers, keeping them warm and free of frost. This saves excavation expense, saves on concrete, and better insulates your house, a win, win, win proposition. Ours was the first that the Summit County inspectors had ever seen.

Diagram of typical versus shallow depth frost free footer design

pouring concreteThe next novel feature of our footers and foundation was the composition of the concrete we used. We used a 50% fly ash mixture which greatly reduces the embodied energy of our concrete. Concrete manufacture accounts for 5-10% of the world energy use. Also by using the 50% fly ash mixture we are recycling a toxic byproduct of coal fired electric plants. Additionally the mixture ends up with a final cure strength that is twice as strong as the conventional concrete mix. The men pumping and smoothing the concrete thought it was faster and easier to work with as well. The only drawback is that it takes twice as long to cure.

The next feature of our footers prompted the Summit County inspector to request engineering documents. We placed EPS not only on the sides of the footers, but also underneath…which they had never heard of. The concern is easy to understand, when you realize the incredible amount of weight that is going to be supported by the EPS (Styrofoam) underneath the footers. We were able to do it by using special extra dense EPS, and by making the footers cover a much larger surface area than typical to spread the pressure out over a large area. Additionally the sides and tops of the footers were also wrapped with 2 inches EPS, even the foundations walls were wrapped with EPS. Even the narrow gaps between pieces of EPS were foamed to prevent heat sinks. Click to see pics

Another Green feature of the foundation is that it is waterproofed with Ecobase instead of the traditional black tar based material. It is a more environmentally friendly way to water proof the foundation. We even put it on top of the foundation, and along with “ecoseal”, which is a polymer based gasket, allowing us to replace the traditional practice of using the thin blue “bubble wrap” called sillseal and the treated lumber. This allowed us to created a more airtight and durable seal between the foundation and the SIP panels, and saved money as well.

Finally, the last unusual feature of the base of house was the 8 inches of EPS (R32) that was placed on the ground before pouring the basement cement floor. Typical practice is to pour the concrete directly onto the gravel underneath, even if radiant floor heating is used. The temperature of the soil beneath a house is about 55 degrees, while the temperature inside a house is commonly 70-72 degrees. If you radiant heating in your floors, like we have, the fluid is typically heated to 80-85 degrees. The laws of thermodynamics tell us that more of the heat will be “sucked” up by the ground than the air inside the house because of the larger temperature difference. Therefore by placing the EPS underneath our heated basement floor we can greatly reduce our heating load.