How To Pour Concrete Footings Under an Existing Concrete Patio

Concrete footings are an important part of a structure like a pergola or a deck, and they provide the solid foundation and support for the rest of the structure. Get installation tips and advice on pouring concrete footings for a pergola or deck under an existing patio from the experts here.

Need to pour a new concrete slab? Learn how to DIY your own concrete patio here.

If your patio just needs an upgrade, here are 9 ways to update your concrete slab (and yes, you can paint it!)

You don’t need to tear up your existing concrete for a sturdy foundation for your next patio project. 

When you’re ready to add a pergola or a deck to your concrete patio, you can keep the concrete slab AND pour new footings! I’m showing you how — and you can see the beautiful pergola I build on top of these footings here.

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What is a Concrete Footing?

A concrete footing is the bottom part of a foundation. For outdoor projects like a pergola or a deck, footings are used to anchor the posts securely to the ground. Footings are critical to ensure that the structure has a strong foundation and can hold up to regular use and inclement weather.

Deck and pergola footings are typically set deep into the ground for added stability. There are options to install a pergola without footings, but for a large project like this, I always recommend the longevity and safety of in-ground footings.

Types of Post Footings

For a deck or pergola, there are many options for laying the footings and installing the posts. Here’s a brief overview of the 3 standard deck and pergola footing options — and remember to check with your local council or office to ensure that your footings will meet building code.

In-ground footings with buried post

This is a very common footing installation, and can be done with or without a concrete block at the bottom. Lauren and Brett used a buried post footing for the viral fire pit pergola with swings.

For this footing install, a deep hole is dug and the post is placed in the hole, leveled and plumbed, and then the hole is filled with concrete or soil.

For added security (and to meet code in many areas), this type of footing often includes a concrete block (either pre-made or fresh poured) at the bottom of the footing hole.

Buried footing like this requires lumber treated for ground contact (pressure-treated).

This also limits the height of the pergola or deck posts (or increases the cost of a tall pergola, to buy longer posts) since part of the posts are buried in the ground.

Premade deck footing blocks

Premade deck footings blocks (pier blocks) can be a good option for a small deck that is not attached to the house, like our outdoor pool deck. Deck blocks are NOT recommended for use as pergola footings.

A poured footing will be stronger and last longer than using deck blocks, especially in areas with severe weather, so I typically recommend going that route. Some codes do not allow using pier blocks for certain projects, so again, be sure to check your local regulations.

To use pre-poured deck blocks (piers), the soil is compacted and leveled to provide a foundation for the block. Then the block is placed and leveled and the post is placed in the block, where it is held in place by the shape of the concrete block (and gravity/the weight of the deck).

Deck blocks don’t require lumber treated for soil contact, but they are limited in the sizes of lumber you can use and the strength of the footing.

Poured concrete footings

For a professional-level install and the best durability, go with poured concrete pier footings!

In a poured concrete footing install, a hole is dug to regulation size, which will depending on the size of the post, the soil content, and the depth of the frost line in the area. Then, concrete is poured in the hole, either directly in the hole or by using a concrete tube form, to form the footing pier.

A post bracket can be either set in the wet concrete before it cures, or attached to the concrete pier using bolts after the footing has cured (like I did with this big beautiful pergola.)

Poured concrete footings are the best method of adding concrete footings to an existing concrete pad.

What is your local Frost Depth?

Frost line depth is the depth to which the ground freezes during the winter. Footings should typically be at least 12″ below the frost depth to prevent heaving (moving up) during the coldest months.

Footing Dimensions

The dimensions of your post footings will vary based on the structure dimensions, local frost depth, and local soil conditions.

For this project, the footings are going to be 8″ wide and more than 30″ deep.  The size would vary depending on the type of structure you would be building.

You would need to first consult with an engineer and have plans approved before installing your footings to make sure they are big enough for your project.

BEFORE YOU DIG: Call 811 to have the utilities marked. Do not dig until you know where the lines are!

Site Preparation

When you are pouring in-ground post footings, you want to make sure that the ground is stable and well-compacted prior to digging the footing holes.

For pouring concrete footings in an existing concrete patio — that work is already done for the patio foundation, so you just need to clear the patio.

Materials and Tools to Pour Concrete Footings for a Pergola or Deck

Once you’ve decided the layout of your pergola or deck posts (and consulted an engineer about proper placement, depth, and reinforcement), you’ll need these materials and touls to pour the concrete footings beneath the existing concrete slab.

Materials

Tools

Did you know? You can rent tools like an auger, angle grinder, hammer drill, and cement mixer from your local Home Depot.

Step by Step: How To Pour Concrete Footings Under an Existing Concrete Patio

Step 1: Lay Out The Footing Locations

Based on your design, locate the placement of footings and mark the center of each footing with an X.

I like to use white tape stuck on the concrete because it makes the marks easier to see and is a better writing surface. Then, use an awl and hammer to mark the center of the of X.

Keep the layout square with the 3 – 4 – 5 Rule. Use your tape measure to measure out 3 feet from the corner one way (x-axis) and 4 feet from the corner the other way (y-axis), and, if it’s square, when you measure the two markings at a diagonal the distance will be 5 feet. (Remember the Pythagorean theorem? ?)

Step 2: Cut Holes in the Existing Concrete

There are 2 options for cutting holes in a concrete slab: an angle grinder and hammer drill, or a concrete hole press (bore press).

Angle Grinder and Hammer Drill

Cutting a hole in concrete using an angle grinder and hammer drill takes some time, but costs less than renting a concrete hole drill.

You’ll score the edges of the square hole with the grinder, and then use the hammer drill to break up the concrete into pieces to remove it.

This is a good option for cutting a 10-12 square inch wide hole.

Concrete Hole Drill (Bore Press)

A concrete hole drill will cut a nice clean circular hole in the concrete slab. I prefer this when I can because it saves time and gives a very clean cut edge.

Renting a concrete hole drill typically also means hiring the professional who runs the drill. Local prices will vary, and in my area of central Utah, I paid $100 per hole. Definitely worth it for the time and mess saved!

After the core was cut, I used a hammer drill to break up the core to remove it from the hole.

Note that the concrete hole drill does require one additional hole to anchor the large drill, but that is easily patched after.

BEFORE YOU DIG: Call 811 to have the utilities marked. Do not dig until you know where the lines are!

Step 3: Dig the Holes Beneath the Concrete Patio

Use a post hole digger and/or auger to remove the dirt to dig the holes.

I planned to rent an auger, but the soil beneath the patio was a good soil: loamy clay soil and easy to dig by hand. So I dug the holes manually with the post hole digger. It took me about 30 minutes per hole to dig my 30-inch deep holes.

If the soil had been rocky, like it often is in my area, I would have needed to rent an auger.

If the soil had been sandy and less stable, I would have also needed to add a concrete tube (sonotube) for added stability for the footing.

Step 4: Suspend Rebar Before the Pour

This pergola required footings with 28 inch #4 rebar in the center, 3 inches above the bottom of the hole for added tensile strength. (Remember, consult a professional engineer and your local code to know what rebar is required for your footings.)

The easiest way to position the rebar is to place a piece of scrap wood across the hole and suspend the rebar using baling wire. This holds it in place for the pour and is easy to remove.

BONUS: Add Watering System

This client knew they wanted to have hanging planters on the pergola, so before we poured the footings, the landscaper stopped by to run some pipe from the main sprinkler system up through the footing hole. This made it easy for them to tie a drip system for hanging planters into their regular watering automation.

Step 5: Pass Inspection Before Pouring

Once all the pieces of rebar where suspended, I was able to call and have the inspector come and approve the holes.

Depending on your project size and local area codes, you may or may not need the holes inspected. Because of the size of this pergola, I did.

I dug my holes slightly bigger than required to be on the safe side, and, after clearing some debris from a previously buried railroad tie, passed inspection.

Again, soil conditions (such as sand) may require a sonotube (concrete tube) to create a more uniform concrete footing, if soil is less stable or sandy.

Step 6: Protect the Concrete Pad

Before you mix and pour the concrete in the hole, be sure to protect the existing concrete pad! This keep your patio clean and will make the difference between your finished footings looking like an inexperienced DIY job and looking like a pro.

In a piece of plywood, cut a hole the same size as your concrete hole, and place the plywood directly over the hole. Then pour the concrete through the plywood hole into your footing.

Step 7: Mix and Pour Concrete

You can rent a concrete mixer or mix by hand like we did in a wheelbarrow.

I used an online concrete calculator to figure how many total bags we needed. We ended up using about 2.5 80# bags of concrete per hole, and each hole took about 30 minutes to mix and pour.

Just follow the instructions on the bag to add the water to the right consistency. Then pour and scoop the concrete into the hole. The plywood will keep the splashback from getting on the patio!

As the concrete gets to the top of the footing hole, remove the plywood and carefully smooth out the top of the footing.

Tip: Pouring concrete into dry soil may pull the moisture from the concrete and result in a weakened cure. If the soil in your footing hole is very dry, consider dampening it (but not enough to create standing water in the hole), or using a concrete tube. Properly moistened soil (or a prepared concrete tube) will keep cracks to a minimum and give the strongest pour.

Step 8: Level the Concrete

After the concrete has cured a bit, you want to level and smooth the top of your poured footing, to match the concrete patio level and finish.

Use a small trowel to level the top of the footing with the concrete patio and bring the “cream” to the top. Smooth out the top of the footing.

Concrete “cream” is top layer of concrete that is primary smoother cement with no gravel aggregate visible. Bringing it to the top gives you a really nice looking finish and helps the surface strength.

Step 9: Attach Post Bases

Now you’re ready to attach post bases for your deck, gazebo, or pergola to your DIY concrete pier footings. For this pergola, I used these Simpson Strong Tie Concealed Post Bases — see the rest of the pergola build details here.

Conclusion

Pouring concrete footings beneath your existing patio is a great way to have the foundational stability you need to add a pergola or deck and make your patio an amazing family hangout!

Concrete Footing FAQ  

How deep should concrete footings be?

Concrete footings need to extend below the frost line. See the map and links above to determine the frost depth for your area.

Do I need rebar in footings?

Most footings require at least some rebar reinforcement. Check your local building codes and consult with a structural engineer for your project.

How do I calculate concrete footings?

Determining the number and placement of concrete footings for a pergola or deck will depend on the size and layout of the deck and width of your posts.

Consult an engineer and your local building code office to ensure you have adequate support for your structure.

Is a footer necessary on a concrete slab?

To build on top of a concrete slab, you can use a bracket designed for that purpose to anchor your pergola, gazebo, or deck straight to the existing concrete slab, if you prefer that over a footer. The slab will typically need to be crack-free and at least 4″ thick with a recommended 12″ total depth on the outside edge.

A concrete footer like we showed above will give you much more strength and durability, since it is dug much deeper into the ground than the concrete slab is poured.

Pouring a concrete slab? For a patio, driveway or sidewalk, no footer is needed. For a foundation of a home, garage, or shed, YES you will need a footer for the foundation. That’s not what this tutorial covers ?

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I am the husband of the amazing Cassity of Remodelaholic. I love to problem solve and to design and build things inside and outside the house to make life better. I am a professional Landscape Architect by trade and love the outdoors.

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