concrete or wood piers?

[Submariner]

Originally Posted by Zymer

I have heard that wrapping the posts with several layers of polyethylene is supposed to prevent them from being 'pulled' up in this manner. The layers of plastic 'slide' so that the post isn't pulled.

YMMV, I don't know for a fact if it works but is *sounds* plausible.

Many people have told me about doing that. [wrapping a sonotube with garbage bags]

I have a big project coming up this summer and I was planning on using sonotubes wrapped in plastic. However now seeing the plastic cones, I am wondering if these might be better.

[Trailmonkey]

Since the plastic forms are tapered, the frost tends to lift away from the pier, rather than grabbing it and lifting. However, if you are using wood, don't scrimp on the pea gravel and drainage, and wrapping it in poly will tend to help prevent the frost from getting a good hold on it. Frost is wily, though, and will grab the pier that is the hardest to get to and repair...

[Submariner]

How does pea gravel effect frost heaving?

[kellysmith]

Originally Posted by forest beekeeper

How does pea gravel effect frost heaving?

I don't agree that a little pea stone in the bottom of the hole will do much. The concept is that the pea stone will provide drainage. But if there is no where for the water to go once the pea stone is saturated, it might make you feel better, but won't prevent water from accumulating and frost action when it freezes. Google "rubble foundation" and you will see another concept that might actually work. If the entire load bearing trench is built so that water can escape, there won't be much frost movement. But, saturated ground will freeze and frost movement will occur because water expands when it freezes. Frost not only causes an up and down movement, but any post below ground will be pushed downhill. So if you have an area not totally level, say the building is on posts or sauna tubes where the building is level, but the posts are 6 inches above grade on one end of the building and the posts are 18 inches above grade on the other end. The posts will be kicked toward the downhill end of the building by frost over time. Use the footing tubes and they will never move. The tubes are 60 inches tall, and if you put them 5 ft underground, you will never have frost move them because the bell flair on the bottom is just too much surface below the frost line.
I also will say that anything that only sits on the ground will be moved by frost. The more water that saturates the ground, the more frost movement. The problem is that frost will go deeper under the outside of the building than it will near the center because the building provides some heat protection. Frost breaks rocks, it will move your building with no effort if there is water that freezes in the ground under the building.