By properly pouring concrete footings for posts, you can avoid frost-heave damage.

Your deck footings should be dug and poured so that they are below the frost line. Aside from using the traditional deck footings, you can also utilize the concrete footing blocks.

They won’t heave or move as the ground freezes and thaws with the change in the weather if positioned below the frost line. This article describes how to create strong foundations that will stand firm all year long.

Map of Deck Footing Frost Depth

Two factors determine the depth of your deck footing. In order to support the concentrated load applied on each deck pier, you must first have adequate soil conditions. The depth you need to dig to go below the frost line in your town or city must then be determined by consulting a frost depth map or speaking with your local building inspector.

You might be curious about the frost line’s depth. It can differ greatly. The depth of the frost can reach more than eight feet in the coldest regions of the USA. The depth of the frost may be less than one foot in areas of the country that are warmer.

The Frost Line: What is it?

The depth below which soil moisture is anticipated to freeze is known as the frost line. The soil beneath your footings won’t freeze in the winter until the bottoms of your footings are buried below the frost line due to the remaining heat in the earth.

Depending on your location, you may need to put your frost footings at a different depth. If you live in a warm climate, such as South Florida, where frost is infrequent, you might be able to set your footings directly on the ground, but in really cold climates, such as Minnesota and Canada, you will need to dig down at least 96 inches.

Always ask your local building inspector what is needed in your community. Additionally, footings must be inserted at least 12″ below unstable soil. The minimum distance to grade must be maintained both vertically and laterally if you are building into a steep hillside or next to a retaining wall.

You might need to dig your foundation much deeper than on flat terrain to achieve an appropriate lateral barrier.

The Frost Line in Construction: Why Is It Important?

Making sure the structure’s base won’t move over time is your first concern while building anything. Just as you shouldn’t build on the unstable ground where the weight of the building will produce uneven downhill settling that could lead to the structure’s collapse, you also don’t want your deck to lift up unevenly.

Things weighing hundreds of pounds can and do get lifted by frost heaving. The uplift force produced by the expanding freezing water can lift the footing and anything on it should the soil beneath the footing freeze. The enormous uplift force might seriously harm the structural integrity of your deck.

How Does the Soil Freeze Affect Things?

The soil that is in touch with the air starts to freeze as temperatures drop below freezing. The soil temperature can start to closely match the air temperature if the air temperature is far below 32 F. As a result, the soil underneath the surface layer that has frozen also freezes.

When water freezes into solid form, it expands by 9%. Instead of being driven into the compacted ground, this excess volume is pushed upward into the air.

Like the layers on a sandwich, the liquid water in the soil frequently occurs in layers. Within the soil, these various water bodies turn into ice lenses. Each ice lens that forms lifts the lenses above it higher into the atmosphere. Frost has the ability to readily lift the earth by six or more inches.

Map of Frost Depth

A frost depth map is a helpful tool for estimating how far you should dig into the ground to reach an area where the ground doesn’t often freeze. On a frost depth map, you will frequently find contour lines where any position along the line denotes the frost depth in the towns and cities where the line crosses.

These are merely guidelines, and it’s advisable to speak with your neighborhood building inspector to find out the actual frost depth where you’re planning to build.

U.S. Frost Depth Map

Zip Code-Level Frost Line Depth

You can enter a zip code into internet tools to find out the potential frost depth where you’re building. I’ll say it again: don’t take this information at face value. Get in touch with your local building inspector for the best advice.

Never put your new deck or concrete footings for posts at risk from frost. Only things you cannot control should be your focus of hope. Your new deck footing depth is within your control.

Remember that digging three to four inches below the frost line is not a terrible idea. Deeper is usually preferable since, under some unusual weather situations, extremely cold temperatures might occur over the course of a winter, and your deck or structure will survive while many others may need repairs when the ground thaws.

How Far Does the Frost Line Go?

You have a severe case of “frost heave-osis” if your setting deck posts rise in the spring and then fall back to their original position when the temperature warms. How far below is the frost line then? The earth freezes in the winter from the soil’s surface all the way to the ground.

The kind of soil, the severity of the winter, the amount of water in the soil, and the thickness of an insulating layer of snow all affect how deeply the frost penetrates the soil.

The depth of the frost varies by geography. The frost depth in Minnesota is 42 inches, yet it may only be 1 foot in a warmer state like Missouri.

Ask about the needed frost depth as well as the size and shape of the footings when you speak with your local building department to obtain a building permit. So that the footings’ bottoms are at or below the frost depth, dig the footing holes next.

Here is a brief introduction to the complicated mechanics of frost heave. “Ice lenses” are tiny coatings of frost created when water in the soil around an area gathers and freezes.

Consider how ice crystals are domed above the initial water level in the ice cube tray. When water freezes, it expands by around 9%. Ice presses down with a force of around 50,000 pounds per square inch, which is strong enough to raise even a big skyscraper. A little deck with poor footings has no chance of standing.

Buildings and decks sometimes don’t rise back to their former height because the surrounding ground will occasionally fill in beneath the footing when it is raised.

Heavy clay soils have more issues with frost heave than sandy, well-drained soils since they don’t drain as well. Although footings must be deep enough, ice lenses can nevertheless lift footings and posts from the side by latching onto the rough surfaces of wood and concrete. Because of this, smooth wooden timber deck posts and concrete piers poured into cardboard tubes work effectively for below-grade support.

How to establish firm, frost-resistant Concrete Deck Footings

Hold the cardboard concrete form tube about 12 inches above the bottom of the footing when pouring concrete. To accomplish this, attach the tube’s sides to the 2×4 grid’s center, creating a tic-tac-toe pattern at the top of the hole.

Then pour concrete into the hole’s bottom through the tube. The tube will fill until the large area at the bottom of the opening is full.

Concrete footings with flared sides will resist heaving during hard winters when frost penetrates particularly deeply. Additionally, greater width at the bottom will disperse weight across a wider region.

After the backfill has settled, build up soil around the posts to deflect runoff water away from the post.

Project – Step-by-step in Constructing Solid Concrete Footing

Step 1: Place a Premixed Concrete Order

Premixed concrete should be ordered from a ready-mix supplier if you are pouring more than a few footings. To fill a form tube, you would be surprised at how many bags of concrete mix you would need to mix by hand. So it is advisable to order ta premixed concrete.

Calculate the concrete volume by multiplying the post and column’s height in feet by the tube’s radius in feet squared, multiplied by 3.14. To determine how many cubic yards you need to order, divide the amount by 27. For the wide footing bases, add more extra.

Step 2: The frost line depth chart: Helpful in determining the required post  footing depth

The footing will heave as the earth freezes and thaws if it does not extend below the frost line. Lay the concrete footings by extending below the required frost line by referring to the zip code-level frost line depth.

Step 3: Concrete-set post

The concrete still needs to reach below the frost line even if you’re installing deck posts into the ground rather than on top of footings.

Tools Necessary

Measuring tape
Posthole digger

Materials Requirement


Solid Concrete Footing

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Deck Footings

setup of the deck posts
digging the deck post footing
cutting the post form
height of footing for post
mixing the concrete
post footing with concrete
pouring the conrete
fixing the steel connection
finishing the surface
concrete post below frost line
completed concrete deck footing