When the ground freezes, it becomes a hydraulic ram, crushing or twisting anything in its way. When water freezes, its volume rises by 9%. It can move the footings, foundations, and pipelines in the ground.
The frost line is a critical area of concern for any external construction, from oil pipelines to backyard fences. To prevent frozen pipes and footings from shifting, contractors and DIYers need to understand what a frost line is and the frost level in your area. In this post, you’ll learn how to determine the frost depths and how to thaw frozen ground quickly if you must dig in the dead of winter.
Let’s start with the basic definition of the frost line.
What Is a Frost Line?
The frost line is the average depth that the ground freezes every year. The more severe the winters, the deeper the freeze, and the deeper water pipes and cement footings need to go. Also known as ground freezing depth, the frost line extends from the top of the soil to an average depth but thaws out during the warmer months.
Frost lines are not the same as permafrost that occurs in the northern areas of Canada and Alaska. Permafrost is a subsurface layer of permanently frozen ground.
Why is Meeting the Frost Lines Important?
As water freezes, it expands. If you’ve ever forgotten a can of soda in the freezer, it will swell and burst. It’s the same with water and sewer pipes buried above frost line depths.
The International Plumbing Code states that “Exterior water supply system piping shall be installed not less than 6 inches (152 mm) below the frost line and not less than 12 inches (305 mm) below grade.”
Above the frost line, the ground can heave up, shifting whatever is in it or freezing the pipes’ contents. To avoid these issues, knowing the frost level in your area allows you to construct below-the-ground freezing depths to keep pipes flowing, decks level, and foundations stable.
Want to save time and money when digging through frozen ground? The Powerblanket 5×9 Ground Thawing Heated Blanket can thaw 12-18 inches per day, allowing you to work efficiently even in frigid conditions. These blankets are durable, easy to use, and provide targeted heat exactly where you need it.
How Deep Does the Ground Freeze Go?
The frost line map below is a rule of thumb for frost line depths for the lower 48 states.
Consult your local building codes or inspector for a more accurate answer to how deep the frost level is in your area. They can show you a maximum frost depth map and specify the proper depth you need to dig for footings and pipes.
You can see another interactive map that provides frost lines by state by hovering your mouse over the state.
Are There Any Formulas or Calculations That Can Estimate the Depth of the Frost Line?
Some equations can estimate or predict the frost line depth. Unfortunately, they are Ph. Ph.D.-level calculations, such as this Predictive Modeling of Freezing and Thawing of Frost-Susceptible Soils.
Some of the information and data that goes into calculating the depth of freeze or thaw include
- Maximum daily air temperature
- Minimum daily air temperature
- Estimated pavement surface temperature (for paved roadways)
- Frost depth
- Regression constant
- Average measured frost depth
The best way to find the frost level for your area is to call your local building code agency. They will have the most accurate information.
How Does the Frost Level Affect Digging in the Winter?
Frozen ground can be as solid as concrete. Manually, a pickaxe is the best option to break through the top layer, but it will be very slow going and not practical for long trenches. There are various powered options for Bobcats, backhoes, and excavators. Still, frozen ground is tough on machines and their operators.
For example, to cut through frozen ground, a chain-type trenching machine requires carbide teeth, which cost about $5 each. Contractors report that replacing 90 teeth in a day is not uncommon, costing $450. Replacing an entire chain can cost $1,500 plus the labor and downtime.
The best option is to thaw the ground first using ground-thawing blankets.
Ground Thawing Blankets Can Penetrate Frost Line Depths
Cold weather can have severe negative impacts on construction jobs, trenching, cemetery operations, and more. The best solution to quickly thawing frozen ground is Powerblanket ground thawing blankets.
A ground thawing blanket has heating elements that heat up to 150°F (65.5°C) and uses a standard electrical plug. The heat penetrates to a depth of 12 to 18 inches every 24 hours, depending on the soil and ambient temperatures.
Insulated concrete blankets are not the same as ground-thawing blankets because they do not have heating elements. They simply trap the ambient heat in the ground and reduce the thermal transfer from the air to the ground.
Powerblanket Saves Time and Money
Construction projects can’t afford to wait for the ground to thaw. Busting through the ice-hardened ground is tough on man and machine. Powerblanket ground thawing blankets save many hours of labor. For example, one Idaho cemetery had a ground-freezing depth of 14 inches. Using the Powerblanket to thaw the ground saved hours of digging time. Additionally, they could roll up the sod and reuse it, saving $100 per grave.
Powerblanket ground thawing blankets come in various sizes, which you can compare here.
Time is money. Don't waste time waiting for the ground to thaw. Powerblanket has you covered.
