B
HomeLibrariesCopilotSearchProjectsBookmarksAddress
FeedbackHelp Desk
Libraries
Code LibraryDiagramsAssembliesProductsCalculatorsChecklistsSpecificationsPermitsAddress ReportDOT SpecsModel CodesTransportationRailroadFire SafetyAccessibilityStructuralTransit SpecsUSACE
Jurisdictions
Iowa
Ohio
Utah
Other Jurisdictions
Railroad
AREMA Manual
Accessibility
ADA StandardsPROWAG
PricingLog in
Home / Code Guides / Deck Footings

Deck Footing Requirements — Depth, Size & Frost Protection

Deck footings live or die by two questions: are they below the frost line, and are they big enough for the load? The IRC answers the first with your jurisdiction’s frost-depth map and the second with Table R507.3.1.

RequirementModel Code StandardSection
Frost protectionFootings must extend below the local frost line, bear on solid ground per R403.1.4, or be frost-protected — the local frost depth is set by your jurisdiction (Table R301.2)IRC R403.1.4, R507.3.2
BearingFootings bear on undisturbed native soil or engineered fill; organic soil and uncompacted fill are not allowedIRC R403.1, R507.3
Minimum sizeSized per Table R507.3.1 by tributary area, soil bearing capacity, and live/snow load — small decks on 1,500 psf soil commonly need larger footings than owners expectIRC Table R507.3.1
Minimum thicknessFooting thickness minimum 6 in. per Table R507.3.1IRC R507.3.1
Post-to-footing connectionPosts must be restrained against lateral displacement at the footing — a post base connector or embedment, not just resting on concreteIRC R507.4.1
Free-standing exemptionA detached deck up to 200 sq ft, under 30 in. above grade, not serving the required exit door, may be exempt from a permit — the construction rules still applyIRC R105.2

Worth knowing

  • Frost depth varies wildly by jurisdiction — from 0 in. in the South to 60+ in. in the northern plains. Find yours on your jurisdiction page or in the local Table R301.2 amendments.
  • Precast pier blocks sitting on grade rarely satisfy frost protection in cold climates.
  • Footings within 5 feet of a house wall generally must bear at the same elevation as the house footing or be evaluated for surcharge.
  • The IRC deck provisions (R507) were substantially expanded in the 2015-2021 editions — older span cards are outdated.
Sections cite the 2021 International Residential Code and 2023 National Electrical Code as model standards. This is BuildSpec’s own summary — not ICC or NFPA text; read the authoritative language at codes.iccsafe.org. Your state may be on a different edition with amendments — check your jurisdiction page or get an Address Report.
Deck Ledger →GFCI Protection →Egress Windows →Stairs →Handrails & Guards →Smoke & CO Alarms →