What frost line means
The frost line is how deep the ground freezes in a given area. Footings and water lines go below it so freezing soil does not lift or break them.
Also called frost depth.
Where it matters on a concrete job
Frost depth is set locally and drives footing depth for decks, additions and fence posts. Look it up for the job address and put the depth in the estimate.
What the model code says
- Footings extend below the frost line set in the local design table, unless frost protected by insulation as the code allows. (IRC 2021, Chapter 4)
Check which code edition your building department enforces for frost line before you quote.
What it costs
Jobs that involve frost line are priced in the new foundation cost guide: about $9,250 typical, usually $5,200 to $42,000. The guide shows its sources and what moves the price. The concrete block calculator prices a job line by line.
Work it out
- Free calculator: Concrete block calculator
- Cost guide: New foundation cost
- Tools, templates and guides: Free concrete resources
Sources: 2021 International Residential Code, Chapter 4, Foundations (ICC). Checked October 9, 2026.