But the frost line may be different depending on the climate you live in.
Fence post frost line.
I am not too concerned about concrete providing lateral support for the fence above ground because of the posts depth and 5ft spacing.
Watch the frost line.
Dirt then slips in beneath the concrete.
Even if you put the footing down to the frost line frost can still grab the side of the post or footing and push it up.
The process is then repeated next winter raising your fencing a bit further.
The bottom of the post needs to sit below the frost line consult local codes for exact requirements.
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Fence post depth size and anchoring systems can make or break your fence line.
The best way to prevent frost heave in fence posts is to set them on a drainage bed prior to pouring the concrete.
For example a 6 foot tall fence will need at least 2 feet of post in the ground.
Also where frost only penetrates the soil an inch or two there is no need to be concerned about frost heaves such as on the west coast and the southern most parts of the u s.
Consider the frost line in your area.
Your fencing is raised as a result.
Frost heave is a condition that happens when water freezes in the soil and then the soil thaws out.
Generally a hole that is at least 1 3 the depth of the fence will keep the fence from heaving when the ground freezes.
When building a fence it s important to think about the frost line which is the deepest point in the ground where water will freeze.
Typically in part to ensure that posts lodge below the frost line experts call for a hole deep enough to submerge the bottom third of the post below ground.
However where freezing goes deeply into soil your fence posts and the footings of your deck are subject to this upward pressure.
The frost line also called frost depth varies from region to region.
For a six foot tall post therefore.
It seems like frost wouldn t push up a post if it the post extended below the frost line.
In these cases it s best to surround the post or concrete with a smooth surface of plastic a waxed tube or plastic pipe fig.
The resulting pressure literally heaves the fence posts out of the ground over time.
The trouble begins when frost starts to heave your concrete upward using the tops of those v shaped concrete footings to grip them since the tops form a lip.
C to keep frost from bonding to the sides and jacking up the footing.