Unpopular opinion: deck footings should go 6 inches below your frost line, and I learned that number the hard way

Casey Butler · 2026-10-16T06:10:06.379591+00:00

I built a 10x12 floating deck behind my house in Minneapolis back in 2021 and just set my concrete forms 18 inches down because that felt deep enough, no research, just vibes. Last spring two of the corner posts had heaved almost an inch and my rim joist was bowing, so I finally looked up the actual frost depth for Hennepin County and it is 42 inches. I had to dig out both footings, pour new ones at 48 inches with tubes of forms and about $140 in quikrete, and re-level the whole frame in one weekend. What frost depth did you guys use for yours, and did anyone else just guess like I did?

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Unpopular opinion: deck footings should go 6 inches below your frost line, and I learned that number the hard way | Backyard Builds - Rigidtalk