Footings are the part of a deck nobody sees once the project is finished. But they carry the entire structure above them. Get the elevation wrong down here, and you will spend the rest of the build shimming posts, notching beams, and chasing a fix that should never have been necessary. Get it right, and everything above the footing goes together cleanly.
This guide walks through the process from the first hole in the ground to the anchor bolt that locks the footing in place, including the math that tells you exactly how tall to build each concrete pier.
Start With What’s Underground, Not Just What’s on the Plan
Before any digging starts, you need to know what is buried in that yard. That starts with a call to 811, a utility locating service, to have underground lines marked. It is not enough on its own, though. A walkthrough of the dig area with whoever knows the property best can catch things that never made it onto a locate map.
That extra step matters more than it might seem. In one project, a gas line was hiding almost directly under a planned hole and was narrowly missed. An unmarked cable sat in another hole and was avoided purely by luck. A power line ran through a third. The original footing location actually had to be shifted to get clear of the gas line entirely.
The lesson here is simple: treat the yard as if something is buried everywhere until you have proof otherwise, and be ready to adjust your footing layout on the fly if you find an obstruction.
Digging to the Depth Your Plan and Climate Require
Once the ground is clear, the plan tells you how big and how deep to dig. In this project, the plan called for a 12-inch round hole dug 24 inches deep. Your own plan, soil conditions, and local code will set your actual numbers.
That depth is not arbitrary. It is tied to your local frost depth, the distance below the surface where the ground freezes in winter. If a footing sits above that line, the freezing and thawing soil can push the whole footing upward over time, a problem called frost heave. In one region with only a 6-inch frost depth, a 24-inch hole was more than deep enough to avoid that problem entirely. In a colder climate, the required depth could be much greater. Always check your local building code for your area’s frost depth before assuming any number is safe to use.
If your deck project is permitted, expect an inspector to check the dug holes against the plan before you are allowed to pour any concrete. That inspection confirms the size and depth match what was approved, and it has to happen before the next step.
Figuring out the correct footing depth for your specific frost line, soil, and load requirements is exactly the kind of code-driven calculation that is easy to get wrong by hand. The Sketchronix Engine can help generate a footing depth and layout starting point based on the location and project details you provide, giving you a documented number to bring to your inspector instead of a guess. Always confirm the result against your local building department before you dig.
Poured Concrete vs. Helical Piles: Why This Project Went With Concrete
Some deck builds use helical piles, metal posts screwed deep into the ground with a driver, instead of poured concrete piers. In a yard full of buried utilities, that method carries real risk. Driving a pile blind into ground with unmarked gas or cable lines could mean an expensive, dangerous mistake.
There was also a footing needed that was not called for on the original plan at all, added to help support an extra beam coming off the house. That footing sat in a spot a helical pile driver could not have reached. Hand-digging and pouring concrete gave full control over exactly where each footing landed, obstruction by obstruction.
If your site has a lot of buried utilities or awkward access, this is a good reason to weigh poured concrete footings over piles, even if piles would normally be faster.
A Little Extra Reinforcement
Even when a plan does not call for it, adding rebar to a concrete footing is a reasonable way to add strength and reduce the risk of structural issues down the road. In this case, carbon fiber rebar was added to the footings purely as an extra safety margin, not because the plan required it.
Mixing and Pouring: Setting Up an Efficient System
Hand-mixing dozens of bags of concrete is a lot of physical labor if you do it the traditional way, bag by bag in a wheelbarrow. A mud mixer, available to rent from most equipment rental yards, speeds this up considerably. It is an auger-driven machine that feeds concrete mix through a rotating screw, sprays in water, and blends everything in a single pass. Most models can mix around three 60-pound bags at once, and a jog dial lets you adjust how wet or dry, known as the “slump,” the mix comes out.
For a project needing around 40 bags of concrete, that is roughly three-quarters of a pallet of material. Positioning the mixer on a slight rise so it can pour straight down into a wheelbarrow sitting below saves the effort of hauling the mixer around the yard between batches.
Nailing the Elevation: Where Does the Footing Top Actually Need to Be?
A small mistake here is what leads to shimming and notching later, and getting it right comes down to a bit of subtraction.
Step one: pick a reference point. Mark a point on the house at the height where the finished decking surface should end up. If an old deck is being replaced, its existing height, before removal, is a convenient reference.
Step two: subtract every material’s thickness. Work down from that mark by subtracting the thickness of every layer that will sit on top of the footing: the beam, the joists, the decking boards, and any standoff base hardware between the post and the bracket. In one project, that added up to roughly 15 inches for the beam and joists combined once a small margin for error was added, plus 1 inch for the decking and 1 inch for the standoff base, for a target of 17 inches. That left about a quarter to three-eighths of an inch of play for shimming later, tight enough to avoid a sloppy fit but with just enough room to make small adjustments with shims.
Step three: translate that number to a laser line. A rotating laser level set up anywhere convenient on the site projects a level line you can read anywhere in the yard, including down inside a hole. Since the laser will almost never sit exactly on your reference mark, measure the difference between the two and add it to your target number. In this project, an offset of 1 and 3/4 inches was added to the 17-inch target, giving a final number of 18 and 3/4 inches from the laser line down to where the top of each footing needed to land.
Working out this string of measurements by hand, and getting it wrong by even a small amount, is exactly the kind of error that turns into shimming and notching later. The Sketchronix Engine can run this same subtraction for you: enter your beam, joist, decking, and hardware dimensions, and it returns a target top-of-footing elevation to work from, so you’re checking your tape measure against a calculated number instead of doing the math on the fly.
Cutting the Concrete Tube to the Right Height
Concrete piers are typically formed using a round cardboard tube, sometimes called a quick tube, that gets filled with concrete and stripped away once it cures. To figure out how long to cut one, measure from the top of the freshly poured concrete in the hole up to the laser line, then subtract your target number. In this project, that measurement was 28 inches to the laser, and subtracting the 18-and-3/4-inch target left 9 and 1/4 inches of tube needed above the concrete. Adding roughly 4 inches of tube to be pushed down into the wet concrete for stability brought the total cut length to about 13 inches.
Setting and Leveling the Tube
Push the cut tube a few inches into the wet concrete so it holds itself upright while you finish filling around it. Check its height against the laser line, and trim it down if it is sitting too high. Use a torpedo level against the side of the tube, checked from a couple of different angles, to make sure it is standing plumb rather than leaning. Packing a bit of dirt around the base can help hold the tube steady while the pier top gets filled.
Consistency across every footing matters as much as getting any single one right. Aim to keep every footing within about a quarter inch of the others in height. A laser level is what makes that level of precision realistic across a whole yard full of holes.
Finishing the Pour and Setting the Anchor Bolt
Once the tube is filled, a light pass with a concrete vibrator helps release trapped air bubbles and settle the mix, but over-compacting can work against you, so use it sparingly. A trowel smooths the top, and gently tapping the edges helps bring some of the finer, wetter concrete “cream” to the surface for a cleaner finish.
The last step is setting a J-bolt, a bolt bent in a hook shape, down into the wet concrete near the center of the pier. Once the concrete cures around it, that bolt anchors a metal bracket to the top of the footing, and that bracket is what the beam eventually sits in. There is some room to adjust its exact position later, so it does not need to be perfect, but it should be roughly centered under where the beam line will run. Letting the concrete firm up for around half an hour before setting the bolt can make it easier to hold in place while you position it.
Repeat, Then Move On
Every footing in a deck goes through this same sequence: dig, inspect, pour, set the tube to elevation, finish, and set the bolt. Once every footing hits the same target height within a small tolerance, the framing above it, from beams to joists to decking, goes together far more predictably than if even one footing is off.
Disclaimer
This article is provided for general informational and educational purposes only. Construction techniques, measurements, tool specifications, and material requirements vary by project, region, and local building code, and readers should independently verify all details before beginning any work. Sketchronix Insights makes no guarantees as to the accuracy or completeness of this information and is not liable for any damages, injuries, or losses resulting from its use. For structural, permitting, electrical, or safety-related questions, consult a licensed contractor, structural engineer, manufacturer documentation, or your local building department.