Guides

• Why the Frost Depth Here Is Not the Number Your Inspector Uses — The frost line in the building code is a value each jurisdiction adopts, not a measurement. How it differs from a physics estimate, and which one wins.
• When the 12 Inch Footing Minimum Is Deeper Than the Frost — In 1,050 of 3,144 US counties the estimated frost depth is 12 in or less, so the IRC 12 in footing minimum sets the dig depth instead.
• Why Frost Goes Deeper Under a Plowed Driveway Than Under Snow — What the ground surface does to frost depth: the same county worked out under snow, gravel and asphalt, from a published table of surface n-factors.
• How Each County's Frost Depth Is Worked Out, and Where It Is Weakest — NOAA daily normals to a freezing index to the Modified Berggren equation, step by step, with the counties where each step is least certain.