Codes & compliance · Glossary
Frost line
Also called: frost depth
The frost line is the maximum depth at which the ground freezes in a given climate. Foundation footings and exterior post bases must be poured below the frost line to prevent frost heave. Frost line depth varies by region: 6 inches in Los Angeles to 48 inches in parts of the Pacific Northwest.
Why this matters for renovation projects
Frost line shows up on permits, contracts, or estimates that Renology covers across LA, San Diego, San Francisco, Seattle, Portland, and Denver. Most homeowners encounter the term once a project is already mid-flight, when there is no time to learn its mechanics without slowing the contractor. Knowing what it means before signing the contract is the difference between a clean project and an avoidable surprise. For how Renology calibrates cost ranges against permit valuations and contractor invoices, see the methodology.