[Daveayres]

I live on the edge of a wetland in Northern Wisconsin. The 4x4 posts and footings that support my deck are in water-holding soil. During the winter when the ground freezes down two to four feet, the deck posts heave up anywhere from three to seven inches. When the ground thaws in the spring and summer the posts do not settle back down because (I assume) soil works in under the posts and footings, thus preventing them from returning to original height.
Has anyone constructed a deck on wet soil? Any suggestions on how to redo the footings to prevent heaving in the winter? I would like to avoid starting from scratch. The deck is in great shape. I just want to redo the footings somehow to prevent heaving.
Thanks in advance for any suggestions.

 

[Grampa Bud]

Posts and/or footings will stay put if they are set at freeze depth or lower. If you can't get there from where your deck is at now, then you might try pouring a 6 in. thick x 4 ft. dia. 'floating footing' at grade and anchoring your deck post to the center of the circle. The ground will still heave slightly in winter, but since you would be 'floating' it will settle in the spring when the frost is gone.

 

[Scuba_Dave]

Where are you located?

oops nevermind..........

But the footings need to extend down past the frost line
Except - like a pond - if it freezes around the post - it can then lift the post as the ground freezes
It shouldn't (I thought) if it is down past the frost line as that would anchor it down

 

[jomama45]

You guys get frost in Northern Wisconsin!? :laughing:

Seriously, what are the posts sitting on at the bottom, assuming you know?

 

[Daveayres]

You guys get frost in Northern Wisconsin!? :laughing:

Seriously, what are the posts sitting on at the bottom, assuming you know?

Yea, our ground is still frozen solid. Still have 10 inches of ice on our lake.
Posts are resting on cement blocks at bottom of 40 inch deep holes. The builder who put in the deck couldn't get any deeper due to water. I want to fix this without his help, if you get my drift.

 

[Daveayres]

Posts and/or footings will stay put if they are set at freeze depth or lower. If you can't get there from where your deck is at now, then you might try pouring a 6 in. thick x 4 ft. dia. 'floating footing' at grade and anchoring your deck post to the center of the circle. The ground will still heave slightly in winter, but since you would be 'floating' it will settle in the spring when the frost is gone.

Real good suggestion, I think! Your idea is along the line I was thinking. At grade, ground doesn't heave very much. \
Thanks!! :yes:

 

[jomama45]

Dave, ther's only 2 ways these posts (& the deck) can be heaving. The first would be that frost is "picking" at your posts. The second is, obviously, your post pads aren't deep enough. Wet ground, Northern exposure, low-snow conditions can all take frost well below 40" in your area.

BTW, even I (who has spent alot of time in th UP) can believe you have that much ice left!

 

[Fleener]

I also have a cabin in norther wisconsin near (or should I say "on") a wet land. When I dug the holes, they started filling up w/ water just above the frost line - not sure if I got to 40" or not. I think code is 42 or 48". What most people in my area do is, dig as low as you can, drop the post and back fill with pea gravel or slightly larger gravel. Try to fill with rock, not the crushed rock / sand that comes with it. When the ground freezes, the rock will prevent it from getting a good grip on you post. I've had my post in for 2 winter - so far so good. Another neighbor used that method and it has lasted longer with good success.

One neighbor used a floating footing on top of the ground. His deck looked pretty rough last week. Not sure I understand why that method did not work for him. Maybe there are rocks below that are getting pushed up?