How Deep Should Deck Footings Be?

Deck footings are the concrete mini foundations that provide support to your backyard deck. Footings serve as the anchors on which the rest of your deck structure floats. Deck support posts are mounted within your deck footings and serve as the attachment points between the structural elements located above and below ground. When installing deck footings, depth is a key consideration. The soft soil, more prevalent near the surface, may be softer and more likely to shift or wash away. It is also important that your deck footings are located below the frost line to prevent freezing and cracking over time.

Things You'll Need

Post hole digger
Shovel
Wooden post

Tape measure
Tubular concrete molds
Work gloves

Instructions

- 1
  Check with your local building authorities to find out the frost depth in your area. The frost depth differs from place to place based on seasonal temperature averages, the height of the water table and the soil makeup. The frost line in your area will determine how deep you should dig your deck footing post holes.
- 2
  Check with local building ordinances to discover where your deck footings can be placed legally. If you place the footings in the wrong locations, you can end up being fined and having to move the deck to a new location. If water, sewer, gas or power lines run through your property, you will also have to consider their location before breaking ground on your concrete footings.
- 3
  Use your post hole digger to make a hole into which your concrete footing will be poured. Dig the hole deep enough to allow all of the concrete to sit 6 inches below the frost line. Dig each hole so that the bottom fourth of the hole is wider than the top. The proper shape for a footing is an inverted cone. The extra width at the bottom, allows the concrete to disperse its load more efficiently and will create a more stable foundation.
- 4
  Use your shovel or a piece of wooden post to flatten the bottom of the hole. Remove any rocks, loose soil or other debris from the bottom of the hole to ensure a firm foundation.
- 5
  Dig each hole so that it has a surface opening between 12 and 24 inches. The larger the hole, the easier it will be to access and to pour concrete into.

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