Deck Footing Spacing Requirements: Complete Guide to Safe Post Placement

Deck footing spacing isn't negotiable—it's determined by engineering, lumber span tables, and building codes. Space footings too far apart and your deck sags, bounces, or worse, collapses. Space them too close and you waste time, money, and concrete. The right spacing depends on your beam size, joist span, and expected loads. Once you understand the relationships, determining optimal spacing becomes straightforward.

Quick Answer: Most residential decks use 6-foot footing spacing with double 2×10 or 2×12 beams carrying 2×8 or 2×10 joists spanning 8-12 feet. This configuration safely supports standard 40-50 psf live loads. Spacing beyond 8 feet typically requires engineered lumber (LVL or glulam beams).

The Three Factors That Determine Footing Spacing

Factor #1: Beam Size and Species

The beam spanning between footings is the primary limiting factor. Standard beam configurations and their maximum footing spacing:

Critical Note: These spans assume 40-50 psf live load. Hot tubs, heavy planters, or crowd loads require closer spacing or larger beams.

Factor #2: Joist Span

Longer joist spans transfer more load to beams, which may require closer footing spacing:

• Short joist span (8-10 feet): Less beam load, can use standard spacing
• Medium joist span (10-12 feet): Moderate beam load, standard spacing works
• Long joist span (12-16 feet): Heavy beam load, may need closer footings

Example: A deck with 2×10 joists spanning 12 feet puts more load on the beam than one with joists spanning 8 feet. This might reduce maximum footing spacing from 7 feet to 6 feet.

Factor #3: Load Requirements

Building codes specify minimum design loads:

• Live load: 40-50 psf (people, furniture, snow)
• Dead load: 10-15 psf (deck structure weight)
• Total design load: 50-65 psf

Special loads requiring closer footing spacing:

• Hot tubs: 50-100 psf concentrated load
• Built-in planters: 100+ psf with wet soil
• Roof overhead: Additional dead load
• Snow load areas: Up to 70 psf in heavy snow regions

Standard Deck Layouts and Footing Counts

12×12 Deck (144 sq ft) – Attached to House

Layout Option 1: Single Beam Row

• Joists: 2×8 spanning 12 feet from ledger to beam
• Beam: Double 2×10 running parallel to house, 6 feet from house
• Footings: 3 footings spaced 6 feet apart along beam line
• Total footings: 3

12×16 Deck (192 sq ft) – Attached to House

Standard Layout:

• Joists: 2×8 spanning 12 feet from ledger to beam
• Beam: Double 2×10 running parallel to house
• Footings: 4 footings spaced 5.3 feet apart (16 feet ÷ 3 spans)
• Total footings: 4

16×20 Deck (320 sq ft) – Attached to House

Standard Layout:

• Joists: 2×10 spanning 16 feet from ledger to beam
• Beam: Double 2×12 running parallel to house
• Footings: 4 footings spaced 5 feet apart (20 feet ÷ 4 spans)
• Total footings: 4

Note: This pushes 2×10 joists near their 16-foot limit. Consider engineered joists or a mid-span beam for better performance.

20×20 Deck (400 sq ft) – Freestanding

Two-Beam Layout:

• Joists: 2×10 spanning 10 feet between beams
• Beams: Two rows of double 2×10, each 20 feet long
• Footings per beam: 4 footings (spaced ~6.7 feet apart)
• Total footings: 8

Advanced Footing Layouts

Corner Footing Placement

Footings should typically be placed 6-12 inches inside the deck perimeter, not directly at corners. This allows:

• Room for beam overhangs (improves load distribution)
• Fascia board installation space
• Access for maintenance
• Better aesthetics (posts hidden behind rim joists)

Cantilever Considerations

Deck framing can cantilever beyond the beam, reducing the number of footings needed:

• Standard cantilever: Joists can extend 1/4 of their total span past the beam
• Example: 2×10 joists spanning 12 feet can cantilever 3 feet beyond the beam
• Benefit: A 15-foot-deep deck might only need a beam 9 feet from the house (12' span - 3' cantilever)

Cantilevering reduces footing needs but creates bounce at deck edges. Use conservatively.

Multi-Level Decks

Each level requires independent footing calculations:

• Upper and lower levels can share footings IF properly engineered
• Typically easier to use separate footing systems
• Ensure upper level posts don't interfere with lower level functionality

Common Footing Spacing Mistakes

1. Exceeding Beam Span Limits

The #1 dangerous mistake. "My neighbor's deck is fine with 10-foot spacing" doesn't mean it's code-compliant or safe. Over-spanned beams sag visibly and can fail catastrophically.

Reality check: If your deck bounces noticeably when walking, footings are likely too far apart.

2. Ignoring Diagonal Measurements

Footings must be square to the house and to each other. A deck that's out of square by 2-3 inches creates framing nightmares and weak points.

Solution: Use the 3-4-5 triangle method or measure diagonals (must be equal).

3. Inconsistent Spacing

Footings spaced 8', 6', 5', 7' along one beam create uneven load distribution. Some posts carry more weight, increasing failure risk.

Best practice: Equal spacing across each beam for uniform load distribution.

4. Forgetting Load Concentrations

Planning a hot tub, outdoor kitchen, or built-in seating? These areas need:

• Additional footings (reduce spacing by 30-50%)
• Larger footings (increase diameter/width)
• Engineered design (hot tubs often require professional engineering)

5. Wrong Footing Size for Spacing

Wider footing spacing concentrates more load per footing. You might need larger footing diameters:

• 4-5 foot spacing: 12" diameter footings adequate
• 6-7 foot spacing: 14-16" diameter recommended
• 8+ foot spacing: 18-20" diameter or engineered design

Calculating Exact Footing Spacing

Step-by-Step Process

1. Determine joist direction and span
   • Will joists run toward the house or parallel to it?
   • What's the distance from ledger board to beam?
   • Choose joist size based on span tables for that distance
2. Identify beam location(s)
   • Where do beams need to run to support joist ends?
   • Can you cantilever to reduce beam distance from house?
3. Select beam size
   • Based on joist span and deck width
   • Consult span tables for your wood species
   • Double 2×10 is the sweet spot for most residential decks
4. Determine maximum footing spacing
   • Check span tables for your beam size
   • Typical range: 6-8 feet for dimensional lumber
5. Calculate actual spacing
   • Measure beam length
   • Divide by maximum spacing to get number of spans needed
   • Number of footings = spans + 1
   • Actual spacing = beam length ÷ number of spans

Example Calculation: 12×16 Deck

1. Joists: 2×8 spanning 12 feet perpendicular to house
2. Beam location: 12 feet from house (at joist ends)
3. Beam: Double 2×10 SPF (max span 7 feet)
4. Beam length: 16 feet
5. Calculation:
   • 16 feet ÷ 7 feet max = 2.28 spans → round up to 3 spans
   • Footings needed: 3 spans + 1 = 4 footings
   • Actual spacing: 16 feet ÷ 3 spans = 5.33 feet

Result: 4 footings spaced 5.33 feet apart along the 16-foot beam

Footing Depth Requirements

Spacing and depth are separate but equally important:

• Minimum depth: Below frost line in your area
• Frost lines range: 12" (deep South) to 60"+ (Upper Midwest)
• Attached decks: Must match house footing depth

No matter how perfectly you space footings, if they're too shallow, frost heave will destroy your deck.

Special Situations

Ground-Level "Floating" Decks

Decks under 30 inches high and not attached to structures can sometimes use precast concrete blocks instead of deep footings:

• Still requires proper spacing (6-8 feet typical)
• Blocks must rest on compacted gravel base
• Not suitable in frost-heave areas
• Check local codes (many prohibit this method)

Hillside and Sloped Decks

On slopes, footing spacing stays the same, but posts vary in height:

• Maintain equal horizontal spacing
• Uphill posts are shorter, downhill posts are taller
• All footing tops must be level (use string line)
• Tall posts (>6 feet) may need mid-height bracing

Composite and PVC Decking

Composite materials don't change structural requirements:

• Footing spacing remains the same
• Framing lumber does the structural work
• Some composites require closer joist spacing (12" vs. 16" OC)
• This affects beam load but usually doesn't change footing spacing

Code Compliance and Inspections

Common Code Requirements

• Minimum 40 psf live load (50 psf in some jurisdictions)
• 10 psf dead load
• Footings below frost line
• Minimum 12" diameter or 12"×12" square footings
• Span tables from IRC (International Residential Code) or local amendments

Inspection Checkpoints

1. Footing inspection (before pouring):
   • Depth verification
   • Spacing measurement
   • Soil condition assessment
2. Framing inspection:
   • Beam size and installation
   • Joist size and spacing
   • Ledger board attachment
   • Flashing and weather protection
3. Final inspection:
   • Guardrails (required if deck over 30" high)
   • Stair construction
   • Overall structural integrity

Cost Impact of Footing Spacing

Footing Material Costs (per footing)

• Concrete (12" diameter, 48" deep): $25-$40
• Post base hardware: $8-$15
• Post (6×6 × 10'): $45-$75
• Labor (if hired): $75-$150 per footing

Total per footing: $150-$280 DIY, $225-$430 professional

Closer Spacing Trade-Off

Example: 16-foot beam

Option A: 8-foot spacing (3 footings)

• Footings: 3 × $200 = $600
• Beam: Double 2×12 × 16' = $120
• Total: $720

Option B: 6-foot spacing (4 footings)

• Footings: 4 × $200 = $800
• Beam: Double 2×10 × 16' = $90
• Total: $890

Cost difference: $170 – The extra footing costs more, but you save on beam lumber. More importantly, closer spacing provides better support and less bounce.

Expert Tips for Optimal Footing Layout

1. Use the 6-foot sweet spot – Six-foot spacing works with double 2×10 beams (most common) and creates comfortable layout geometry
2. Draw it out first – Sketch your deck to scale, plot footing locations, and verify spacing before digging
3. Consider beam length availability – Standard lumber comes in 2-foot increments (8', 10', 12', 14', 16', 18', 20'). Design around these lengths to avoid splicing beams
4. Account for diagonal bracing – Leave room between footings for cross-bracing if posts are over 6 feet tall
5. Mark everything twice – Use batterboards and string lines to mark footing locations. Double-check all measurements before digging
6. Document your layout – Take photos with measurements for future reference (deck repairs, additions, modifications)
7. When in doubt, add a footing – An extra footing costs $150-200 but eliminates bounce and adds peace of mind

Final Takeaway

Deck footing spacing isn't creative—it's calculated based on beam capacity, joist loads, and building codes. The 6-8 foot range handles most residential scenarios with double 2×10 or 2×12 beams. Closer spacing provides better support and less bounce. Wider spacing requires larger beams or engineered lumber.

Don't guess or copy your neighbor's deck. Look up the span tables for your lumber species and size, calculate the number of footings needed, and space them equally. This simple process ensures a safe, code-compliant deck that lasts decades without sagging or bouncing.

Use our deck calculator above to determine material quantities based on your specific dimensions. Get your footing layout approved during the pre-pour inspection, and you'll have the foundation for a deck you can trust for generations.