How to Install Deck Footings

As a decking pro with decades in the industry, I can tell you this: A rock-solid deck starts with strong footings. After all, footings are literally the foundation of any successful deck project. Here, I’ll walk you through the essentials to get your new deck off on the right foot(ing).

Before we dive in, it’s important to understand why footings matter. Footings, which support your posts or beams, distribute the deck’s weight by increasing the surface area in contact with the ground. This reduces ground pressure, preventing settling, shifting, and potential structural damage. The bottom line: Footings provide a stable base that supports the entire deck structure.

In this guide, you’ll learn:

• The different types of deck footings and when to use them
• How to prepare your deck site and set your footings
• A step-by-step approach to pouring concrete footings

Types of Deck Footings

Footings might be out of sight, but they’re essential for your deck’s stability and longevity. Let’s take a closer look at the common footing types and their suitability for your deck project.

Poured Concrete Footings

Poured concrete footings, or concrete piers, involve placing forms in the ground and filling them with concrete. Then, you attach post bases or anchors to the cured concrete which will hold your posts or beams. Don’t embed deck posts directly into the concrete; this isn’t code-compliant in many areas due to stability concerns and the risk of rot. These footings are a popular choice for most deck projects.

Pros:

• Versatile for various deck sizes and loads
• Strong and durable
• Suitable for different soil conditions
• Customizable for specific design needs

Cons:

• Labor and time-intensive installation
• Can be messy
• Requires curing time

Buried Post Footings

Buried post footings are wooden (or metal) posts set directly into holes in the ground. The posts are deeply buried for stability while still extending above ground. However, check your local regulations: They may prohibit wood posts from being in direct contact with soil. Where permitted, this method is suited to smaller decks with lighter loads in areas with stable soil.

Pros:

• Simple and relatively quick to install
• Lower material costs
• Effective in well-drained soil with minimal shifting

Cons:

• Limited load-bearing capacity
• Potential for uneven settling
• Wood posts susceptible to rot
• Not recommended for wet or clay soils or frost heave zones

Precast Concrete Footings

Precast concrete footings are ready-to-use concrete blocks that are placed on leveled ground. Simply insert your deck posts (or beams) into the slots or holes. The weight of the deck keeps them stable. These footings are usually used for smaller decks or when time is a factor, though they may be suitable for larger structures depending on codes and design.

Pros:

• Convenient and quick
• No concrete mixing or curing
• No fasteners required
• Consistent quality and dimensions

Cons:

• Fixed sizes and shapes may not fit all designs or load requirements
• Heavy and cumbersome
• Can be difficult to level

Deck Blocks

Deck blocks are smaller, lighter concrete or plastic blocks used as a deck support base. Similar to precast concrete footings, just level the blocks on the ground and insert your deck posts or beams. Deck blocks are typically used on smaller, unattached decks on stable soil.

Pros:

• Budget-friendly
• Easy to install
• No digging
• Ideal for small to medium-sized decks
• Suitable for extremely hard soil or concrete where digging isn’t practical

Cons:

• Limited load-bearing capacity
• Not ideal for larger decks
• Not be suitable for all soils, particularly soft, loamy, clay, or sandy soils, or those that are likely to heave due to frost
• Not recommended for attached decks

Screw Piles / Helical Piles

Screw piles are long, metal screws with helical blades that are driven into the ground using hydraulic machinery. Brackets or plates are then attached for connecting your deck posts or framing. This method is particularly useful in areas where digging is difficult.

Pros:

• Quick installation
• Immediate load-bearing capability
• Can be installed in various soil conditions
• Ideal for sloped or uneven ground
• Minimal site disturbance

Cons:

• Expensive
• Specialized equipment required
• Installed by professionals; not a DIY project

How to Install Deck Footings

Let’s roll up our sleeves and get started! Here, I’ll describe the steps for installing the various types of deck footings you might want to tackle yourself. While not every step will apply to all footing methods, I’ll highlight the relevant techniques for each type as we go along.

(Don’t worry, if the installation seems like more than you want to take on as a DIY project, you can always find a builder to bring your deck dreams to life.)

Note: Always comply with your local code requirements.

Step 1: Site Prep & Footing Calculation

Clear away vegetation, rocks, and debris from your deck site. I recommend marking the locations of your deck posts using stakes and string to visualize the layout and ensure accurate footing placement.

Determine how many footings you’ll need by calculating the spacing based on your deck’s size and load requirements. Typically, you’ll place footings in a grid pattern, spaced 4 to 6 feet apart for precast concrete footings or deck blocks, and 4 to 8 feet apart for poured concrete and buried post footings. Your deck design, local building codes, and manufacturer guidelines will determine exact spacing.

If you choose precast concrete footings or deck blocks, just level the ground and place them. You may need to dig a shallow hole or trench to level the footings (I like to add gravel underneath for added stability), then backfill with a small amount of soil or gravel.

Step 2: Dig Footing Holes

Digging footing holes is the next step for poured concrete and buried post footings. Remember, safety comes first! Plan ahead and call the 811 hotline before digging to have underground utilities located and marked. (And while you’re at it, check out these tips for deck safety, too.)

The depth and width of your holes depend on local codes, deck size, and soil conditions. Here are some general guidelines:

• Depth: Dig below the frost line to prevent frost heave, which can disrupt your deck’s stability. If you need to know your local frost line, search for a frost depth map online.
• Width: The hole should be 2-3 times the diameter of your deck post, or for poured footings, a bit larger than your concrete tube (which should be 2-3 times the post diameter).

For easier digging, I recommend using a post-hole digger or auger.

Step 3: Position the Footings

For buried post footings, place your posts into the holes and brace them to keep them upright and aligned. Backfill with a soil and gravel mixture and tamp to secure the footings. Continuously check for level—I like to place my level on top of a straight board—and make necessary adjustments.

Step 4: Pour the Concrete

If you choose poured concrete footings, this is where the pouring comes in! Here’s the process:

• Prepare the Forms: Place cardboard concrete tubes inside the holes to create forms for your footings, making sure they’re level and secure. I add wire mesh or rebar inside for extra strength to handle heavy loads and challenging soil conditions.
• Mix the Concrete: Choose an outdoor concrete mix and follow the manufacturer’s instructions. Aim for a consistency that’s pourable but not runny.
• Pour the Concrete: Fill each form with concrete just below the top edge, leaving a small gap for leveling. Backfill around the tube with soil for support.
• Level and Tamp: Use a trowel or board to level off the concrete. Tamp the concrete to remove air bubbles and create a solid base. This can be done by repeatedly striking the form’s edge and sides with a mallet, but I suggest renting a concrete vibrator, which is more effective and less labor-intensive.
• Curing: Allow the concrete to cure according to the manufacturer’s instructions, including guidance on the curing period (typically 24 to 48 hours) and moisture maintenance. Preserving the moisture content in your concrete is essential for optimal strength. There are two primary curing methods:
  1. Water Curing: Keep the concrete surface continuously moist by covering it with wet burlap or spraying it with water and re-wetting it several times a day or as it begins to dry.
  2. Curing Compounds: Apply a liquid membrane-forming compound to the surface of your freshly poured concrete. This creates a consistent, waterproof barrier to retain moisture.

Step 5: Attach Deck Supports

Once the concrete has cured—or if you’ve elected a non-poured footing—you can attach your deck supports to your footings.

For poured concrete footings, this typically involves using galvanized or stainless-steel post anchors or brackets secured with concrete screws using a ramset or powder-actuated tool. I recommend renting this: Powder-actuated tool can be expensive, and most homeowners won’t frequently use one.

For precast concrete footings or deck blocks, insert your deck posts (or beams) into the holes or slots. Additional fasteners aren’t generally needed; the weight of your deck will hold them in place.

Check that your posts or beams are plumb and level for all footing methods before attaching your deck joists.

Investing time and effort into a solid foundation ensures that your deck will stand strong and provide years of enjoyment. Remember: A great deck begins with strong footings!