Building Foundations

What is a Foundation?

What does it do?

  • Simply put, the foundation of a building keeps a structure from settling, sinking, and moving as a result of climate and geological forces imposed on the structure.
  • The weight and depth of a foundation also serves the purpose of anchoring your structure on your property when the wind blows.       Think about a tent blowing down the beach at the lake … no foundation.

I Already Have a Slab

This is usually not a good thing

  • Any permanent building must be built on a properly designed, inspected and approved foundation.
  • Existing slabs more than likely:
    • Have not been inspected.
    • Do not have the proper depth or reinforcement to act as a foundation
    • Are probably not level and /or square
    • Will not be accepted by any inspector as a foundation 
    • May not have proper drainage away from itself

Now What?

  • IF:
    • Your slab is level and square and to your knowledge was reinforced properly as a foundation 
  • AND
    • The slab is located in a position on your property that is an allowable location to build an accessory structure
  • AND
    • You can convince a registered professional engineer to sign-off on the slab design as it exists.
  • THEN
    • It can probably  be used to build one our many garage design on it.


    • Build a building larger than your slab outside the existing slab on a new foundation
      • This may or may not work depending on lots of considerations
    • Tear it out and start over
    • Cut the slab and place a new foundation on the perimeter.
    • Keep using it as a basketball court.

Design Considerations for Foundations


In the most basic form of the building code, all foundations must be dug at least 12″ into the virgin, undisturbed soil.  On top of that, there are frost line requirements that require the bottom of the foundation to be at least 18″ deep below the surrounding grade.  The further north you go, the deeper your foundations must be.

Sloping grades can make these depths difficult to achieve, resulting in either:

  • Removing a bunch of material from a hill to make a flat spot
  • OR Digging the footing excessively deep to get into the virgin soil and importing a bunch of material to balance out the slope.

Sloped lots also present challenges for controlling drainage around and away from the foundation.

Perfectly level lots often need to have material imported to build up a pad so that drainage away from the foundation can be maintained.