How to Install and Build Deck Footings

Types of Concrete Deck Footings

There are several approved ways to support a deck with concrete footings, each with its own advantages depending on soil conditions, load requirements and installation preferences. Some methods focus on simplicity and low cost, while others offer greater resistance to frost movement or higher load-bearing capacity. The following options represent the most common footing styles used in residential deck construction.

#1 Cylindrical Pier Footings

Cylindrical pier footings are simply made by digging holes and filling them with concrete.

Pros

• Among the easiest footings to install; just dig holes
• Among the least expensive to install
• Don’t require form tubes

Cons

• Tops need to be level with the ground, which can hasten post rot
• Frost can sometimes grab hold of rough edges and lift the piers

#2 Concrete Form Tube–Style Footings

Concrete form tube–style footings are the same as cylindrical pier footings but include form tubes.

Pros

• Easy to install
• Smooth edges make it difficult for frost to lift the piers
• Top surfaces can be raised above grade to help keep posts dry

Cons

• Require purchasing form tubes
• Require purchasing post base anchors

#3 Bell Footings

Bell footings are created by digging holes and flaring out the bottoms with a shovel. The larger footprint helps support heavier loads, which can make them a good choice for decks that need to support heavy additions such as hot tubs.

Pros

• Require digging smaller holes than Modified Bell Footings
• Large footprints can support heavier loads
• Unlikely to heave if the bells are below the frost line
• Don’t require form tubes

Cons

• Difficult to flare out the bottoms in extremely sandy soil, heavy clay or when footings need to be deeper than a few feet
• Tops need to be level with the ground
• Require more concrete
• Require purchasing post base anchors

#4 Modified Bell Footings

Modified bell footings have larger footprints like bell footings, which makes them well suited to support heavier loads. They are typically made by digging holes the size of the bottom pads, placing smaller form tubes inside the holes, and then backfilling around the tubes.

Pros

• Large footprints can support heavier loads
• Unlikely to heave if the bells are below the frost line
• Require less concrete than bell footings

Cons

• Require digging larger holes than other footing styles
• Require purchasing form tubes
• Require purchasing post base anchors

#5 Embedded Posts

Embedded posts are installed by digging holes, positioning the posts, and pouring concrete around them. Some inspectors require large bolts or sections of rebar to pass through the bottoms of the posts to prevent them from pulling out of the concrete.

Pros

• Provide the most lateral support
• Don’t require post anchors or form tubes

Cons

• Harder to place and keep posts in the exact right position relative to the frame
• Posts are more likely to rot sooner than in other systems
• May require digging larger holes
• More problematic if a post is cut too short by accident
• Frost can sometimes grab hold of rough edges and lift the piers

What is a helical pier deck footing?

Helical piers are installed by driving helical piles into the ground like large steel screws. The specialized equipment used to install them also determines the required depth by monitoring the torque needed to rotate the pile. Once the proper depth is reached, a post anchor plate is attached to the top of the pile.

Helical piers can be a good solution when building a deck on unstable soil or on large deck projects where a ready-mix truck cannot access the site and the number of footings required makes mixing bags of concrete impractical.

How much do deck footings cost?

For smaller projects, mixing bagged concrete is more practical than ordering a ready-mix truck. For example, a 12-inch-diameter x 36-inch-deep footing requires about 2.35 cubic feet of concrete, which equals about four 80-lb bags of premixed concrete. If each bag costs around $6, the total comes to about $24 per footing, not including hardware such as post bases or anchors.

If you have a bunch of footings to pour, say 10 or more, and the site is accessible to a truck, you could save time and your back by ordering from a ready-mix plant, but because there is a minimum order and hefty delivery fee, plan to pay double.

When planning your footing budget, don’t forget about the form tubes and post base anchors. A 4-foot x 12-inch diameter concrete form tube costs about $17. Post anchors can run from about $15 for a 4x4 anchor to over $60 for a decorative 6x6 option.

Footing Depth, Size & Layout

In most areas, deck footings must extend below the frost line, which is the depth the ground freezes in winter. Frost depth varies widely across the United States. In southern Florida, it's less than 1 foot, while in northern states such as Minnesota or Maine, it can reach up to 8 feet. Online frost-line maps provide general guidance, but you should always confirm the requirement with your local building department.

Footing size and layout should never be guessed. They depend on several structural factors determined during the deck design process, including:

• The load bearing on each footing
• The strength and type of soil supporting the footing
• The design of the deck beams and posts

Most decks require a building permit, and inspectors often check footing holes before concrete is poured. When applying for your permit, confirm the required footing size, depth, and layout and ask whether a footing inspection is required. To learn more about deck footing layout, check out this article about how to install deck footings.

Locate Utilities Before You Dig

Before digging your deck footings, it’s important to know what is buried below the surface. Striking underground utilities such as gas, electrical or communication lines can be extremely dangerous and costly to repair.

A free public utility locating service can mark most underground utilities. In the United States, you can request this service by calling 811. Contact them at least three days before you plan to dig so crews have time to mark the lines.

Be aware that private utilities and underground hazards, such as electrical lines, propane tank lines, irrigation systems, and landscape lighting wires, will not be included in the free service. Before the locator service arrives, clearly mark the perimeter of your planned deck so technicians know where digging will occur.

Tools and Materials Needed to Build Deck Footings

The tools needed to build deck footings vary depending on soil conditions and the type of footing specified in the deck plan. In many cases, basic hand tools are enough to dig the holes and mix the concrete, though additional tools, which can be rented, can help with layout, leveling, mixing and digging in difficult soil conditions.

• Tape measure: Used to measure and locate footing positions during layout

• String and stakes: Used to establish straight layout lines and mark the deck hole

• Hammer: For pounding in stakes

• Layout flags or ground-marking paint: Used to clearly mark footing locations before digging

• Spade shovel: Used to dig the footing holes

• Post-hole digger: Ideal for digging and removing soil from deeper holes

• Long pry bar, pinch bar or digging bar: Helps break up compacted soil

• Reciprocating saw: Useful for cutting through tree roots encountered while digging

• Rotary hammer with drill bits and spade or chisel bit: Used to drill holes for post anchors and can help loosen very compacted soil

• Power auger (optional): A rented drilling tool that quickly bores footing holes

• Level: Used to ensure footing forms are plumb before placing concrete

• Laser level (optional): Helps establish consistent footing heights

• Utility knife: For opening concrete bags

• Garden hose or bucket: Used to add water to the concrete

• Hoe: Used for mixing concrete

• Wheelbarrow: Used to move excavated soil and mix concrete

• Cement mixer (optional): Used for mixing bags of concrete

• Poking stick: Used to remove air pockets from the concrete

• Trowel: Used to smooth the top of the concrete

Materials

• Concrete

• Concrete form tube (if necessary)

• Rebar (if necessary)

• Post base anchor (if necessary)

Step 2: Lay Out and Mark Footing Locations

After determining the proper spacing, size and depth for your footings, use a tape measure to locate them and mark the spots with ground paint or marking flags. If you need more than two footings in a row, locate the outer two first, then use stakes and a string line to keep the rest perfectly aligned.

Step 3: Dig the Footing Holes

Use a combination of a spade shovel and a post-hole digger to dig the footing holes. If you encounter extremely hard soil, use a long pry bar, pinch bar or digging bar to break it up. A rotary hammer with a spade or chisel bit can also work well for loosening compacted soil. If you dig too deep, make sure to compact any soil you replace in the hole. 

Step 4: Cut, Insert and Level the Tube

Insert the tube, then cut it to the desired height with a circular saw. As you backfill around the tube, pack the soil firmly with a board or similar tool to hold the tube in place. Use a level to make sure the tube stays plumb. This will help ensure the top of the footing is level. Rotate the level 90 degrees and check in two directions as you go.

Step 5: Have the Footing Holes Inspected

Depending on local building department requirements, footing holes may need to be inspected before the footings are installed. Schedule the inspection as required and do not pour the concrete until the holes have passed inspection.

Step 6: Mix the Concrete

Mix the concrete in a wheelbarrow or large mixing tub using a hoe. Read the instructions on the concrete bag to determine how much water to add. The mixed concrete should have the consistency of thick oatmeal. Do not add so much water that the mix becomes soupy. Too much water weakens the concrete.

Step 7: Add Rebar if Required

Concrete has tremendous compressive strength, so adding rebar is usually unnecessary for footings unless they extend far above ground and require additional lateral support. Check with your building inspector to determine whether rebar is required. If the footings will support a hot tub or a heavier structure such as a porch or gazebo, the inspector may require an engineer to specify the size, amount and placement of the rebar.

Step 8: Place the Concrete and Eliminate Air Voids

Shovel the concrete into the hole and poke it down with a stick to eliminate any air pockets. If the form tube extends well above the ground, lightly tap its sides with a hammer to help the concrete settle and release trapped air.

Step 9: Smooth the Top

Use a concrete trowel to smooth the top surface of the footing. If you don’t have a trowel, other flat tools can work just as well, such as a drywall taping knife or the smooth side of a tiling/flooring trowel. Smooth the surface evenly and avoid leaving a low spot in the center where water could collect.

Step 10: Install the Post Base Anchor

There are two basic types of post base anchors: those installed while the concrete is still wet and those installed after the concrete has cured. Anchors set into wet concrete generally provide better hold-down strength but must be positioned accurately when inserted. You may also need to clean up or re-smooth the surrounding concrete after placing them.

Anchors installed after the concrete has cured are typically attached with expansion or wedge anchors. The advantage of these types of post bases is that they allow you to fine-tune the post location as you begin laying out the deck frame. While base anchors should be located as close to the center of the footing as possible, shifting them slightly to achieve a perfectly plumb post is usually acceptable.

Whichever post base anchor you choose, follow the manufacturer’s installation instructions.