Building Science Projects

Slab-on-Grade Foundation Best Practices

On-grade foundations are a popular design in Interior Alaska. This project uses modeling software to address these questions:

  • A shallow frost-protected foundation  relies on heat loss to the ground to keep the soils beneath the footing above freezing. What’s the optimal amount of subslab insulation to use to achieve this goal while maximizing energy efficiency?
  • The Design Guide for Frost-Protected Shallow Foundations (prepared by the U.S. Department of Housing and Urban Development) is based on the assumption that the bearing surface of the building foundation is uninsulated in order to maintain heat flow into the soil.  What is the energy loss due to this strategy?  Alternatively, what is the right amount of insulation that could be used beneath the foundation bearing surface that both saves building energy while maintaining frost-free soils beneath the bearing surface?
  • How much “wing” insulation do I need to use if I increase the amount of subslab insulation?

This project will help builders evaluate the most cost effective, energy saving, and safe insulation options for under the slab. A resulting online calculator will help builders and homeowners make decisions about foundation insulation.­


TitleTypeResource Link
Frost Protected Shallow Foundation Insulation CalculatorExternal Links, Calculators

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Shallow Frost-Protected Foundations SnapshotSnapshots



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