Q&A of the Week: Building Foundations on Bedrock

I recently answered a subscriber’s question about building a foundation on bedrock – one of the best options for support any new building.

Q: How can I build a home foundation on bedrock? I really like the idea and simplicity of cutting foam concrete forms to follow the bedrock, but my building inspector is unfamiliar with this and wants some engineered drawings.

A: The issue isn’t all that complicated. I’ve had great results using insulated concrete forms (ICF) to contain the concrete, not primarily because of the insulation value of ICFs, but mostly because the foam is easier to custom-cut to conform to the undulations of bedrock. As long as the undulations are minimal, this is much easier than wrestling with standard plywood forms.

As with any foundation on bedrock, it’s wise to pin the concrete to the rock with rebar set into epoxy in holes. The only question then becomes the spacing of this rebar and rebar size. I’m a big fan of fiberglass rebar since it can’t rust. I don’t use bare steel rebar any more since I’m concerned about rusting and the destruction of concrete that it can lead to. A civil engineer can produce the stamped drawings your inspector wants.

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– Steve Maxwell