What Size Rebar for Deck Footings?
Practical B500B bar-diameter, cage layout and concrete cover guidance for deck post footings — with a worked material estimate and DIN 488 / EN 10080 supply information.
Why Deck Footings Need Rebar
A deck footing (also called a post pad or pile footing) transfers the load from a timber or steel post down into the ground below the frost line or zone of seasonal movement. Unreinforced concrete footings can crack under the eccentric loads imposed by wind and live deck loads; rebar ties the footing together and provides tensile continuity that plain concrete cannot.
Typical deck footings take one of two forms:
- Pad footing: a square or rectangular shallow slab, typically 400–600 mm square and 200–300 mm deep, bearing directly on firm ground.
- Pier / column footing: a cylindrical or square bored concrete pier, typically 250–350 mm diameter and 600–1000 mm deep, extending below the frost depth.
Both benefit from B500B ribbed bar to DIN 488 / EN 10080. In Europe, the frost depth can reach 600–800 mm in colder regions; footings must extend below this. Always check local building regulations and confirm designs with a structural engineer.
Typical Rebar for Deck Footings
General guidance — B500B ribbed bar, normal residential deck loads.
| Footing Type | Size | Vertical / Main Bars | Ties / Links | Bar Diameter |
|---|---|---|---|---|
| Pad footing (small deck) | 400×400×200 mm | 4 bars each way | — | Ø10 mm |
| Pad footing (medium deck) | 500×500×250 mm | 5 bars each way | — | Ø12 mm |
| Pier footing (light) | Ø250 mm, 700 mm deep | 4 vertical bars | Ø6 links @ 200 mm | Ø10 mm |
| Pier footing (standard) | Ø300 mm, 900 mm deep | 4–6 vertical bars | Ø8 links @ 200 mm | Ø12 mm |
| Large pad / heavy deck | 600×600×300 mm | 6 bars each way | — | Ø12–16 mm |
Indicative figures for domestic decks. Engineering design required for elevated or heavy-loaded decks.
Rebar Layout in a Deck Footing
Pad footings
In a pad footing, bars are laid as a two-way mat (orthogonal grid) near the bottom of the footing, with a minimum 75 mm cover to the underside where cast against blinding, or 40 mm where cast against a formed void. A post anchor or hold-down bracket is typically cast into the top of the pad — coordinate its position with the rebar cage before the pour.
Pier / column footings
Pier footings use a vertical rebar cage: typically 4 or 6 longitudinal bars arranged in a circle with circular link ties (stirrups) at regular intervals (200–300 mm). The cage must extend to within 75 mm of the bottom of the bore. The post anchor bolt group is cast into the top of the pier and must be located accurately before concrete is placed.
Concrete cover
For subterranean footings in normal ground conditions, a minimum 50–75 mm cover to all rebar is standard under Eurocode 2 (XC2 exposure class). In aggressive ground chemistry (sulfates, high moisture), increase cover or use sulfate-resisting concrete mixes.
Linking to the post
Starter bars projecting from the footing top into a concrete post base, or anchor bolts cast into the pad, must be accurately positioned. Rebar couplers (mechanical splices) provide a neat solution where bar projections would interfere with formwork or post installation.
Worked Estimate: 6-Post Deck, Ø300 mm Pier Footings
Indicative material take-off only — verify from engineer’s drawings.
- Pier spec: 6 × Ø300 mm piers, 900 mm deep, 4 × Ø12 mm vertical bars + Ø8 links @ 200 mm.
- Vertical bars per pier: 4 bars × 1.0 m (900 mm + 100 mm top projection) × 0.888 kg/m = 3.55 kg × 6 piers = 21.3 kg
- Links per pier: 900 ÷ 200 = ~5 links; perimeter of Ø300 cage ≈ π × 240 mm = ~0.75 m per link; 5 × 0.75 m × 0.395 kg/m = 1.48 kg × 6 = 8.9 kg
- Add 10 % for laps & tying wire: ≈ 3.0 kg
- Indicative total: ~33 kg
We supply B500B in 6–12 m stock lengths, pre-bent stirrups / links to your dimensions, and mechanical couplers for Ø12–40 mm. See also our retaining wall rebar guide for adjacent foundation works.
Frequently Asked Questions
What size rebar do I need for deck footings?
How deep should deck footings be?
Do I need ties (stirrups) in a deck footing?
What concrete cover is needed for deck footing rebar?
Can Steel Rebar Germany supply pre-bent stirrups for deck footing cages?
Source German-standard rebar with full export documentation
Tell us your deck footing specification and destination port — we’ll respond with a detailed quotation.