Foundation, p3
Insulation and Drainage
The trench was dug 20 inches wide - 18 inches to accomodate the straw bale width, plus an additional two inches for the foam insulation. The depth was calculated for this area from the Design Guide for Frost-Protected Shallow Foundations, as previously mentioned. This document also provides insulation thickness formulas based on the type of foamboard being used.
Trench with insulation, drain pipe, and "rubble" (stone).
After the trench was dug the foam insulation was placed around the outside perimeter. An thin layer of rubble was then added to hold the foam in place and raise the drain pipe off of the trench floor. The pipe was placed around the center of the trench with holes facing down, and the end of the pipe was run out and away from the foundation at a gentle slope (top of photo), ensuring any water in the pipe would be carried away.