Differences in geography determine the methods used in building a house on a ledge. The type of rock and exact formation of the ledge establish the construction techniques employed. An engineer may need to be contacted for structural advice. He can also provide expert paperwork necessary for compliance with building codes. Each particular site will have its own requirements for connecting a foundation to a ledge. Some locations require blasting while others call for embedded rebar. The shape of the earth determines the placement and depth for each aspect of this type of building.
Remove all topsoil from house site with shovels.
Mark the corners of the building with spray paint.
Drill 6- to 8-inch deep holes into the rock with a diamond drill bit; space these every two feet. Keep the drill bit wet with a spray bottle and use a gentle up and down action to allow the water to get under the bit. The exact position of these bars is dependent on the contour of the base earth and the wall height.
Place No 6 rebar into the drilled holes and secure with epoxy.
Cut foam forms to fit the contours of the house building site.
Brace the rigid foam forms with 2 by 4's to avoid a concrete blowout.
Pour a low slump concrete mix slowly into the foundation forms.