How Install Concrete Deck Footings

Kevin Brown

Installing Concrete Deck Footings

This tutorial provides a simple and efficient method for installing concrete deck footings for a low deck or wood patio.

While there are multiple ways to install footings, we prefer a fast and reliable technique that we have used successfully on numerous occasions. Here’s how to install concrete deck footings:

How Install Concrete Deck Footings

Installing Concrete Deck Footings

The key to successful footings is precise measurement and alignment before placing the posts.

How Install Concrete Deck Footings

Step 1: Measure Your Deck Area and Determine Footing Placements

Start by measuring your deck area and determine where you want support.

Our deck’s dimensions are about 14’ x 25’ (with a portion cut out for concrete steps). Along the long side, we will use five support posts, spaced roughly every 7’.

(Note: Because we are building a pergola above the deck, two of the support posts will be larger beams than these 4×4 posts. Here’s how we installed the pergola posts.)

There is one middle support post along the shorter side and two posts placed in the center of the deck.

How Install Concrete Deck Footings

Step 2: Dig Your Holes

Dig holes to the required depth for your deck height. Because this is a low deck, the holes are about 18 inches. For a 4×4 post, a 12-inch diameter is sufficient.

Avoid going wider than this, as it will require extra digging.

How Install Concrete Deck Footings

When working with different soil types, using a pry bar can help loosen soil that is deeper than a shovel’s reach.

How Install Concrete Deck Footings

Alternate using the pry bar with scooping out the loosened dirt with a small shovel until you reach your desired depth.

How Install Concrete Deck Footings

Step 3: Install a String to Determine Straight Lines

Use string to determine straight lines when installing post holes. This ensures precise alignment for framing installation.

See also  10 Modern Deck Spaces to Inspire Your Summer Backyard

How Install Concrete Deck Footings

Measure two sides where your string will run (e.g., the center string is 7’ from the foundation of the house; the outer string is 14’ out), then attach the string at those points. This ensures a straight line. It’s also a good way to mark level, if you add a level check and adjustment to the stringing.

How Install Concrete Deck Footings

Step 4: Fit the Holes with Concrete Forms

After digging the holes, you need to fit them with concrete forms. For installing 4×4 post footings, a 10” diameter concrete form is suitable. Measure and cut the forms to your desired height.

How Install Concrete Deck Footings

Concrete forms are great for holding concrete in place for footings above ground. But in this case, the concrete support only needs to reach ground level. Use a hand saw to cut the concrete forms to your desired height.

How Install Concrete Deck Footings

Prepare Your 4×4 Posts

Cut your 4×4 posts slightly longer than necessary. For instance, in this example, 8-foot long 4×4 posts were cut into thirds because they only need to extend about 8 inches above ground. It’s always advisable to have a little extra.

The excess post can be trimmed later, so there’s no need to worry about perfect measurements at this stage.

How Install Concrete Deck Footings

Step 6: Determine the Post Placement

Prior to setting your posts in concrete, decide on their exact placement. Once set, they cannot be moved.

Although string was used to establish the hole positions, now you must use string to determine the precise placement of the posts.

In this particular scenario, part of the deck frame is attached to the house foundation, so measurements were taken from the endpoint of that frame. The outer frame will consist of two 2x6s, with an additional 2×8 being mounted on the outside for the finishing side piece. In total, the frame requires 4-1/2” of space beyond the 4×4 posts.

How Install Concrete Deck Footings

Pound a nail at the post alignment point, then run string to the corner. Use a square to determine 90 degrees.

See also  How Are Deck Screws Different Than Other Screws

How Install Concrete Deck Footings

Pound in a stake corresponding to your 90-degree string and tie the string taut onto the stake.

How Install Concrete Deck Footings

You have a straight, 90-degree line from one corner of your deck to the future position of a corner of your deck.

How Install Concrete Deck Footings

To create a precise corner position, check for 90 degrees by running a string perpendicular to ensure accuracy.

How Install Concrete Deck Footings

Align Your Concrete Forms

Place concrete forms in all holes along the strings. The strings should run to the side of the center above your forms. Aim to have your post placement as close to the center of the forms as possible.

If they’re slightly off-center, that’s fine as long as there’s enough room for the concrete to form around the post.

How Install Concrete Deck Footings

Mix your concrete and set your post by following these steps:

1. Position your concrete form and ensure it is ready for pouring.

2. Run about 2″ of water into the bottom of the form using a hose.

3. Mix your concrete according to the instructions provided.

4. Pour the mixed concrete into the form, ensuring it fills the area evenly.

5. Use a level to ensure your post is straight and aligned correctly.

6. Allow the concrete to set and cure according to the recommended time frame.

7. Once the concrete has fully cured, remove the form and check that the post is secure.

By following these steps, you will be able to mix your concrete and set your post effectively.

How Install Concrete Deck Footings

Make sure to have fast-setting concrete that doesn’t need to be pre-mixed. The process is quick and easy with the right concrete mix.

How Install Concrete Deck Footings

Pour approximately 1/5 or 1/4 of a 50# bag of concrete mix into the water in the bottom of your concrete form.

How Install Concrete Deck Footings

Place the post into the concrete and check for level against the string. Make sure that the side of the post near the string only grazes it without pushing it out of place. If it’s not level, pull out the post and adjust it by wiggling it down into the concrete or sliding it until it’s level, barely touching the string.

See also  Deck Framing - Step By Step Guide

How Install Concrete Deck Footings

Level your pour about half bag concrete hole while someone holds post in place. Add little water, then pour remainder concrete mix. Add more water until it couple inches above concrete mix.

How Install Concrete Deck Footings

Use the pointy end of your pry bar to make holes in your concrete. These won’t be actual holes. Instead, the pry bar poking is “mixing” the concrete, finding air pockets and allowing them to escape before the concrete sets.

How Install Concrete Deck Footings

Check for level on perpendicular sides of your post. Your post may have moved, so make adjustments before the concrete sets. It’s fast-setting, so you have a few minutes but not a ton of time.

How Install Concrete Deck Footings

At the end of the day, your post should graze the placement string without pushing it or bending it.

How Install Concrete Deck Footings

Step 9: Repeat on All Footings

Repeat this process for all footing holes, checking for level in multiple directions multiple times on each post while the concrete is fresh. Allow the concrete to cure according to weather and package instructions.

How Install Concrete Deck Footings

You’re almost done with your deck frame. Two of the holes are for pergola posts, which we’ll install using brackets in the concrete.

Leave a comment