Site Work: Pad Completed
As with any building, creating a solid foundation is important as it provides the base for the rest of the structure. In order to improve the thermal performance of the building, as well as reduce construction costs, a slab on grade foundation was designed for the prototype. Typical residential foundations consist of concrete foundation walls that are installed below the frost line on undisturbed soil or compacted gravel. An alternative to excavating and installing foundation walls below the frost line is to install a layer of rigid insulation horizontally under the entire building. This layer of insulation thermally isolates the building from the ground, as well as maintains the earth’s geo thermal heat under the area of the building, and thereby prevents frost heaves at the building’s foundation during the winter months. 
To ensure the thermal performance of the foundation, we installed 6” of rigid EPS insulation under the entire building. The potential liability of installing this thickness of rigid insulation, is that the structure of the insulation can bridge over voids in the compacted layer beneath the building during the foundation installation, but then settle with the weight of the completed construction. To ensure that the substrate is completely smooth and compacted, a layer of concrete and sand called “flowable fill” was installed. This layer of highly aerated concrete is very easy to install and manipulate to create a level and fully compacted substrate. The result of these construction layers and systems is an extremely well insulated and quickly installed foundation. 
Flowable fill is a mixture of coarse sand and cement that is heavily aerated to make it – you guessed it – flowable! It came out of the truck like a frothy milk shake and was easily placed inside shallow forms. When the flowable fill cures it is crumbly and easily raked or dug up which allows for fine tuning and leveling of the pad. 
A layer of high-density insulation will be placed on top of the flowable fill, providing a complete thermal and moisture break between the earth and the building’s concrete footing. The combination of the flowable fill and the high-density insulation are fundamental details that provide the prototype house with a highly insulated foundation at an affordable cost. You can read more blog posts about the GO Home here.
