Why Are Concrete Footings Important for Decks & Foundations?
Answer: Concrete footings transfer your deck’s weight to stable soil, preventing sinking, heaving, or collapse. Without proper footings, frost, poor soil, or heavy loads can crack or tilt your deck.
Key Details:
- Footings must extend below the frost line (typically 36–48″ deep) to avoid frost heave.
- They distribute weight across a wider area than posts alone.
- Code-compliant footings prevent safety hazards and costly repairs.
How Do You Calculate Footing Size and Depth?
Answer: Footing size depends on soil type, deck load, and local codes.
Step-by-Step Calculation:
- Determine load:
- Deck weight = (Deck area in sq. ft.) × (50 lbs/sq. ft. for live + dead loads).
- Example: 12’x16’ deck = 192 sq. ft. × 50 = 9,600 lbs total load.
- Check soil bearing capacity:
- Compact gravel: 3,000+ lbs/sq. ft.
- Clay: 1,500–2,000 lbs/sq. ft.
- Size footings:
- For 1,600-lb load on 3,000-psi soil: 12″ diameter footing (0.79 sq. ft. × 3,000 = 2,370 lbs capacity).
What’s the Best Way to Lay Out Footings?
Answer: Use batter boards and string lines for pinpoint accuracy.
Steps:
- Mark post locations with stakes.
- Set up batter boards 2’ beyond corners.
- Run strings to form a perfect rectangle (check diagonals for squareness).
- Drop a plumb bob where strings intersect to mark footing centers.
Mistake to Avoid: Don’t eyeball measurements—even 1″ misalignment throws off your deck.
How Deep Should You Dig Footing Holes?
Answer: Dig below the frost line (check local codes) and past topsoil.
Guidelines:
- Cold climates: 36–48″ deep.
- Warm climates: 12–24″ (but always below organic soil).
- Poor soil? Use bell-bottom (“elephant foot”) footings for extra stability.
Tool Tip: Rent an auger for hard soil or rocky ground.
Should You Use Tube Forms or Spread Footings?
Answer: Tube forms (Sonotubes) work for most decks; spread footings are better for weak soil.
Comparison:
| Type | Best For | Pros | Cons |
| Tube Forms | Standard soils | Easy to install, cheap | Limited bearing area |
| Spread Footings | Clay/sand | Wider base, more support | 2x cost, harder to dig |
Pro Choice: BigFoot Systems combine tubes + spread footing in one pour.
How to Mix and Pour Concrete for Footings?
Answer: Use 3,000-psi concrete mixed to an “oatmeal” consistency.
Pouring Steps:
- Pre-wet tubes to prevent premature drying.
- Fill holes halfway, then insert rebar (4 vertical pieces per tube).
- Tap tubes with a shovel to remove air bubbles.
- Pour to 2″ above grade and level with a trowel.
Mix Options:
- Bags: 1x 80-lb bag = ~0.6 cu. ft. (for 1–2 footings).
- Ready-mix: Order 0.5–1 cu. yd. for larger decks.
Calculator Tip: Use our Concrete Calculator to find exact bag/yard needs!
How to Set Anchor Bolts and Post Bases?
Answer: Embed J-bolts or post bases while concrete is wet.
Steps:
- Set bolts centered and plumb (use a template if needed).
- Leave 1″ of thread exposed for nut/washer.
- For adjustable bases (like Simpson ABA), attach after curing.
Critical Check: Measure bolt spacing to match your post layout.
How Long Does Concrete Take to Cure?
Answer: Wait 7 days for full strength, but posts can be set after 48 hours.
Curing Tips:
- Cover with plastic to retain moisture.
- In cold weather, use insulating blankets.
- Avoid heavy loads for 28 days (optimal cure time).
When Should You Call a Pro?
Answer: Hire a contractor if:
- Soil is unstable (quicksand, peat).
- Deck is >12’ off the ground.
- You’re unsure about load calculations.
Cost: $150–$300 per footing (vs. $50 DIY)
How to Prevent Common Footing Failures?
Answer: Avoid these mistakes:
Shallow footings (heaving in frost).
No rebar (cracking under load).
Off-center posts (uneven weight distribution).
Fix: Use our Deck Footing Planner to double-check your design.
Final Tip:
“Always pour footings wider and deeper than minimum code—it’s cheap insurance!”
Ready to start? Calculate exact concrete needs with our Deck Footing Calculator → [Insert Calculator Link]