How deep to dig footings for timber arbors
By My Yard Editorial Team · 7/28/2026
The Quick Answer
Set posts below your local frost line — typically 30–42 inches in northern climates — with 6 inches of gravel at the base for drainage. Shallow footings heave and rack the whole structure.
The Witty Breakdown
Check your frost depth with the building department, not a YouTube video from Tennessee.
Gravel under the post matters as much as depth. A post sitting in a concrete cup full of water rots from the bottom up.
Step-by-Step Fix
- 1
Confirm local frost depth and any permit requirement for structures over a certain size.
- 2
Dig 6 inches past frost depth, add 6 inches of compacted gravel.
- 3
Use pressure-treated posts rated for ground contact (UC4A or better).
- 4
Crown the concrete collar so water sheds away from the post.
Pro-Tip / Do Not Do This
Don't set posts in a sealed concrete tube with no drainage. That's a rot factory with a 6-year warranty.
Was this helpful?
Related Guides
Community Comments
No comments yet — be the first neighbor to weigh in.