Quick Summary
The recommended spacing between footings for a deck depends on several factors, including:
– Deck size and shape
– Deck height
– Type of decking material used
– Soil conditions
– Local building codes
In general, footings should be spaced 4-8 feet apart for smaller residential decks up to 10 feet high. Larger decks, multi-level decks, and decks with heavier materials may require footings spaced closer together, such as every 4-6 feet. The local building code will specify exact requirements.
Tightly spaced footings provide more support and prevent bouncing or sagging. They are especially important for taller decks or weak, sandy, or expansive soils. Wider footing spacing can be used for shorter, lighter decks on firm, stable soil.
What Are Footings?
Footings are the foundation that support and anchor the deck frame and transfer its weight into the ground below. They consist of concrete piers placed below ground level.
Deck footings perform several important functions:
– Transfer the deck load into the soil below
– Resist downward forces and prevent vertical settling
– Resist lateral forces and prevent horizontal shifting
– Anchor the deck securely in place
– Raise the deck frame off the ground for proper drainage and air circulation
Footings contain steel reinforcement to strengthen the concrete. In colder climates, footings are placed below the frost line to prevent heaving during freeze-thaw cycles.
Types of Deck Footings
There are several footing options for decks:
– Concrete piers – Pre-cast concrete cylinders or poured concrete that extend into the ground. The deck posts sit anchored on top.
– Poured concrete – Concrete poured directly into holes dug in the ground.Rebar is added for reinforcement.
– Post anchors – Metal brackets that attach to the bottom of posts and anchor to a concrete pad on the surface.
– Screw-in anchors – Helical metal screws that are literally screwed into the ground like a giant wood screw.
Concrete piers are the most common and economical option. Post anchors or screw anchors can also be suitable for smaller decks. Check with local building codes for approved footing types.
How Far Apart Footings Should Be
Proper footing spacing is important to prevent sagging and provide adequate structural support. In general, footings should be spaced:
– 4-6 feet apart for large, multi-story, or heavily loaded decks
– 6-8 feet apart for most standard single-story decks
– Up to 10 feet apart in some cases for smaller or lightly loaded decks
However, the best footing spacing depends on several factors:
Deck Size and Shape
Larger decks require footings spaced closer together – typically every 4 to 6 feet. This provides sufficient support across a greater area. Smaller decks may only need footings every 6 to 8 feet.
Irregular deck shapes also need footings spaced more closely to support angled sections or notches in the deck perimeter.
Deck Height
The taller the deck, the closer the footing spacing should be. Decks higher than 1-2 feet off the ground exert more downward pressure and tend to bounce more if footings are spaced too far apart.
Multi-story decks require very close footing spacing, such as every 4 feet. Otherwise, the upper levels can sway side-to-side objectionably.
Decking Material
Heavier decking materials like stone, concrete, or tile require more closely spaced footings than lighter wooden decks. This helps support their greater weight.
Thicker and more dense deck boards also warrant tighter footing spacing. 5/4 and 2x deck boards are beefier than standard 1x deck boards.
Soil Conditions
Loose, sandy, or wet soils require closer footing spacing than firm, stable soils. The footing lateral load capacity is lower with loose soils, so more footings are needed.
In expansive clay soils, small seasonal soil movements can multiply across greater footing spans, so spacing must be reduced.
In general, a spacing of 4 to 6 feet is recommended for weaker soils. Stronger soils allow up to 8 foot spans.
Frost Line
In cold climates with seasonal ground freezing, footings must extend below the frost line. This is typically 1 to 3 feet minimum. Deeper footings spaced closer together create a stronger foundation.
Local Building Codes
Most municipalities specify their own deck footing requirements based on local conditions and experience. Common spacing guidelines are:
– Decks up to 2 feet high – 8 feet
– Decks 2 to 6 feet high – 6 feet
– Decks over 6 feet high – 4 feet
However, your specific area may require tighter or wider spacing based on past performance. Always check with local building codes for the approved footing span.
Other Footing Spacing Considerations
In addition to the factors above, also account for:
– Footing size – Larger footings can span wider than smaller ones. Minimum sizes are often 8″ to 12″ in diameter or square.
– Joist spans – Space footings to align with the joist layout so joists are fully supported.
– Load distribution – Spot extra footings near heavy loads like hot tubs.
– Angle bracing – Add footings to support angle bracing installations.
– Beam supports – Use footings to support beams needed for long joist spans.
– Stair and ramp supports – Provide dedicated footings under stairs and ramps as needed.
– Obstructions – Adjust footing locations to avoid utilities, roots and other underground objects.
Also consider the deck size, height, materials, and local conditions as described above when planning the supporting footing layout.
Sample Footing Spacing Layouts
Here are some example deck footing layouts and spans for different deck sizes:
Small (10×12) wooden deck, less than 2 ft. high
– 2 footings spaced 10 ft apart
– Footings aligned with joist ends
Medium (14×16) wooden deck, 2 to 4 ft. high
– 3 footings spaced 5 to 7 ft apart
– 1 extra footing under stairs
Large (20×24) wooden deck, approx. 6 ft. high
– 6 footings spaced 5 to 6 ft apart
– 2 extra footings under stairs
– 1 extra footing supporting a beam
Multi-level deck with upper balcony
– 4 main footings at 4 to 5 ft spacing
– 2 footings supporting beams below balcony
– 1 footing under balcony stairs
– 1 balcony footing
These examples illustrate how footing quantity and spacing changes for larger decks and those with higher elevations or non-uniform shapes.
Installing Deck Footings
When constructing the deck footing layout:
1. Plan the deck design and joist layout. Mark the footing locations.
2. Dig holes 12″-18″ in diameter and to the required footing depth for local conditions.
3. Pour concrete into the holes or place pre-cast concrete footing forms.
4. Insert anchor bolts to secure the posts per local code requirements.
5. Allow concrete to fully cure before installing deck framing – typically 3 to 5 days.
6. Check that footings are level across the tops. Grind down any high spots.
7. Set deck posts onto anchors and attach with approved washers and nuts.
8. Build the rest of the deck frame, double check footing spans, and attach decking.
Always refer to local codes for specific construction and inspection requirements. Also consider hiring a structural engineer for deck footing design, especially for complex or high decks.
Properly spaced footings will provide a stronger, safer deck foundation and prevent structural issues down the road.
Conclusion
The recommended spacing between deck footings is typically 4 to 8 feet based on the deck size, height, materials, and local conditions. Large, tall, or heavily loaded decks need footing spacing toward the lower end around 4 to 6 feet. Smaller, shorter, lightly loaded decks with good soil conditions can potentially go up to 8 foot spans in some cases. There are also several other factors like frost line depth, obstructions, and load locations that can influence the ideal footing layout. Always check local building codes for the approved footing spans and construction requirements in your area. With proper planning and installation of footings at the right locations, any deck will be supported safely for years to come.
