How deep do I need to make the post footings for a residential deck in Northern Michigan? The 12" X 20" deck will be less than 2 feet off the ground.
How deep do I need to make the post footings for a residential deck in Northern Michigan
deckfootings
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Best Answer
The post depth depends on the frost line. The size of the footing depends on the soil type under the footing.
You need to dig until at least under the frost line, and then, if you are not on rock or undisturbed/compacted soil, dig until you get there. You can analyze the soil as you dig. The size of the pad of your footing depends on the soil: gravel, sand, or clay. See also https://www.decks.com/how-to/articles/soil-conditions-for-deck-footings
Check with your local municipality, they have this info for you.
Here's a map of the frost line (depths), and you'll see that Michigan is around 55".
From https://www.decks.com/how-to/articles/deck-footing-frost-depth-map :