Building code frost line depth for deck footings
By My Yard Editorial Team · 7/28/2026
The Quick Answer
Deck footings must bear below the local frost line, which ranges from 12 inches in the South to 48+ inches in the far North. Nearly every deck attached to a house requires a permit and inspection.
The Witty Breakdown
The inspection happens at the open-hole stage. Pour before the inspector sees it and you may be digging it back up.
Footing diameter matters too — it's based on tributary load, usually 12–16 inches for typical residential decks.
Step-by-Step Fix
- 1
Get your frost depth and footing size requirement from the building department.
- 2
Call 811 for utility marking before digging any holes.
- 3
Schedule the open-hole inspection before pouring.
- 4
Use proper post bases — no wood in direct contact with concrete.
Pro-Tip / Do Not Do This
Don't attach a ledger board over siding without flashing. That's the single most common cause of deck collapses and rot.
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