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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.

DECK LEDGER & FOOTING — SECTIOND22HOUSERIMJOIST2×8 MIN PT LEDGER½" lag screws or bolts, staggered 2 rowsspacing per Table R507.9.1.3(1) · flash per R507.2.4DECK JOISTJOIST HANGER (ea. joist)BEAM per Table R507.5POST per Table R507.4positive post-to-beam connectionGRADEFROST LINEFOOTING — BEARS BELOW FROST LINEsize per Table R507.3.1 · min 12" below gradeLATERAL-LOAD CONNECTIONhold-down tension devices per R507.9.2 —2 min, 750 lb capacity each (where used)NOTES · IRC 2021 §R507• NEVER attach a ledger over brick veneer or stucco (§R507.9.1.1) · All hardware hot-dip galvanized or stainless (§R507.2.2)• Pairs with the BuildSpec Deck Footing Calculator (IRC R507.3) for footing sizingNOT TO SCALE
Deck footing and post base — IRC 2021 R507.Open full diagram →
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.
This guide is BuildSpec’s own summary, not code text. It cites the 2021 International Residential Code and the 2023 National Electrical Code as model standards. The IRC 2021 text itself is in the Code Library for signed-in members; BuildSpec publishes no NEC text, which is at nfpa.org. Neither is an adoption record: your state may be on a different edition with amendments — check your jurisdiction page or get an Address Report.
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