We are especially proud of the foundation we have built for the home. We have used what is called a Frost Protected Shallow Foundation (FPSF), where insulation is used on the outside of the foundation to trap ground heat (and some residual heat from the home) under the house so that the concrete foundation walls do not have to go below frost depth (typically 42 inches in our area). In fact, the foundation walls on this home only extend 14-16 inches below the final grade around the house. This cuts down significantly on excavation and concrete costs, and makes it safer to work on since the “hole” dug for the home is only a little over a foot or so deep.
Like the vast majority of builders, typically we have poured our foundations in three parts: footings, walls, and slab. In order to minimize the amount of trips by the concrete contractor, we combined the footings and walls into one pour. It is a 12″ wide by 16″ tall footing/wall reinforced by rebar. We also inserted J-bolts upside down into the wall to connect it to the slab later. You can see how the footing/wall was formed and poured in these photos:
Next, after the underground plumbing was complete, the inside concrete forms were stripped away and the inside of the foundation was filled with sand and compacted. The outside forms stayed on to act as a form for the pouring of the slab later:
Next, we laid down the under-slab insulation layer. We chose 2 inch thick (R-10) Dow extruded polystyrene (XPS) because of it’s excellent thermal properties, crush resistance, and the amazing gift-in-kind program that we have with Dow, where they donate their foam products to Habitat affiliates all over the U.S. and Canada. Thank you Dow!!!
Next, a layer of polyethylene sheeting was placed over the foam layer as a vapor and radon gas barrier, then the concrete slab was poured on top of that. The outside metal forms were stripped off and the foundation is complete.
The benefit of this type of foundation is that the entire slab of the home is thermally isolated from the ground under it, which means no cold slab under your feet and drastically reduced heat loss into the ground during the winter.
For more information on the Dow gift-in-kind program with Habitat, click here: