How to Determine the Footing Depth for a Deck

Several factors must be considered when determining the needs for your deck footings. The initial consideration is how many posts are necessary for the deck you are installing. It also is necessary to determine the footing depth for the deck. The bottom of the footing must be below the frost line for your area. This prevents the footing and deck posts from heaving or lifting up when the water in the soil freezes and thaws.

Instructions

- 1
  Contact utility companies to come out and mark the location of underground lines. Ask the representative on the phone about the frost line in your area.
- 2
  Call the building inspector to come out and survey the property. This helps if you have a hill or slope in the area in which you are placing the deck. Footings require a depth at least 12 inches below any unsettled soil. Slopes and hills also require deeper depths to reach the frost line.
- 3
  Add at least 6 inches to the frost line depth for your area. This places the bottom of the footer below the frost line, insulating it from the possibility of heaving in the future. If you are placing crushed rock before the footing, add 12 inches below the frost line.

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