How to Prevent Frost Heave
Roughly 25% of homes will have structural distress at some point in their lifespan, and 5% will have severe structural issues. Approximately 80% of structural problems stem from soil movement beneath the foundation when the soil settles or expands. Frost heave is a significant contributor to soil expansion.
Frost heave happens when the soil expands and contracts during the freezing process. It contributes to a significant number of foundation failures. These shifting soils cause the foundation walls and footings to move, which leads to bulging, cracking, and in some cases, a complete foundation failure.
Vertical ground movements of 4-8 inches are common, and up to 24-inch shifts have happened. A seven-story building can move 2 to 3 inches. Homes, driveways, sidewalks, outdoor basketball or tennis courts, and other structures on your property are all susceptible to frost heave.
Weather changes cause frost heave, but there are still things you can do to avoid frost heave.
What is Frost Heave?
Frost heave is the force of moving soil, and that moving dirt can shift anything sitting on top of it, like a house. The earth moves by expanding and contracting during freeze and thaw temperature conditions, typically in the winter, spring, and fall.
Frost heave occurs when three things are present:
- Freezing temperatures
- Water below ground surface and near freezing point
- Frost susceptible soil near freezing point
It begins when soil turns to ice, which creates an ice lens. Because water expands 9% in volume when frozen, the ice itself causes frost ice heave. The swelled ice lenses push the soil upward, causing the soil to shift. The severity of this shifting depends on how much water is available in the soil. The amount of water depends on a water source and how easily the soil retains water (frost susceptible soil) or if it has good drainage (non-frost-susceptible soil).
Frost susceptible soils have small pores with vein-like cavities that allow water to penetrate and flow through them. Fine-grain soil like silty clay soil, silts, fine sand, rock flour, and clayey gravel are highly susceptible to frost heaving. Those soils are also ideal for forming ice lenses.
Dirty sand, dirty gravel, and glacial tills are moderately susceptible soils. The soils considered resistant to frost heave include extremely clean mixtures of sand and gravel, which promote easy water drainage that does not have capillaries that trap and freeze moisture.
The freeze depth depends on the climate. You can generate a personalized freeze score on various websites, and you will see the depth can range a lot, but the range is typically from 3 feet to 20 feet. A depth of 20 feet probably has frost susceptible soil in a colder climate.
Frost Heave Prevention
To eliminate or minimize frost heave, you must control at least one of these three conditions. You can:
- Keep water out of the freeze zone
- Ensure the soil is not susceptible to frost
- Heat the ground as is done in refrigerated buildings like ice rinks.
- Frost zones and frost depth. Frost depth is the deepest freeze zone at which the ground and groundwater will freeze. It is crucial to know your location's average frost depth because the soil can expand by 9% when groundwater freezes. When building, you will want structural bracing to be below your frost point where it is impervious to frost heave.
- Frost susceptible soil vs frost-resistant soil. When water penetrates the earth, the ground can freeze. The type of soil is a significant factor in its ability to freeze. If you have frost susceptible soil, remove it, and replace it with frost-resistant soil such as extremely clean mixtures of sand and gravel. You can also apply polymer injections.
- Heated dwellings. Heated dwellings rarely suffer frost heave foundation damage because their temperature prevents soil freezes. However, if you do not heat your basement or other parts of your home, it can fall prey to frost heave. Some heated houses still get frost heave due to significant water in the soil caused by heat loss, leaking retaining walls, poor ground drainage, and high frost susceptible soils.
Driveways and other structures like she-sheds also typically do not have a heat source, so you will need good drainage and different strategies to keep the dirt from freezing.
You can take other heave prevention measures to protect your home's foundation and other areas on your property from frost damage.
How to Prevent Frost Heave in Concrete Slabs
There are installation prevention strategies:
- Hire a geotechnical engineer (soils engineer) to examine the soil conditions near the foundation or other affected area. S/he will measure your soil's load-bearing capacity and the necessary footing size you need should you decide to undergo the significant project of excavating the ground near your foundation, replacing it with treated soil, and adding proper footings. Be sure your soils-engineer factors in local building codes.
- The most important thing to do to prevent frost heave in concrete slabs is to keep all water supply lines well below the frost line. Frost heave depends on that water supply to build the force that can cause so much damage.
- Place Styrofoam and a layer of crushed stone below your concrete slab.
- Add a wire screen or steel rebar for extra support and protection.
- Extend your footings below the frost line.
- You can also install a frost wall.
- Use frost-proof concrete.
What is a Frost Wall?
A frost wall protects your house and acts as an insulated wall constructed around the foundation. Frost walls are constructed deep, with foundations below the frost line, to keep the home from being damaged by frost heave.
Materials also play a role in frost heave. While ideal in many ways for foundations, concrete is not resistant to frost heave. The water-filled capillary pores make it vulnerable to temperature changes, especially when there is a water source nearby.
You can create DIY concrete that is more resistant to frost heave by using a lower water-to-cement ratio and adding a unique aeration admixture. One method is polymer injections, which resist water infiltration and stabilizes the soil.
How to Keep Dirt from Freezing
If your soil appears to be growing rocks, your land may be a victim of frost heave. Experts recommended these steps to at least minimize frost heave.
- First, keep water out of the area if possible.
- Do not use the site as a runoff area for excess water.
- You may be able to avoid frost heave by changing the composition of the soil. Add organic matter to your soil in the spring and fall. It loosens soil and promotes drainage.
- Some soil types do not allow water to move as freely through them, so you can prevent frost heave by mixing frost-resistant soil into your own.
- Fill and rake low areas to prevent ponding.
- Add 4 inches of mulch after the first frost, which insulates the soil.
How to Stop Fence Posts from Moving
To keep fence posts from moving, you need to drill down below the frost line, so your posts have a firm foundation. Ensure that all your posts are planted in firm, solid ground so they will not be affected when the ground freezes and swells.
Areas Susceptible to Frost Heave
Watch for the following:
- Inadequate or non-existent ditches where water can drain
- Driveways that create dams by preventing drainage
- Culvert pipes or water passageways under your driveway, between ditches, or elsewhere on your property
- The transition from excavating soil to refilling it
- Abrupt changes in the type of soil from excavation/refill to natural climate changes
Does Home Insurance Cover Frost Heave?
No, unfortunately, frost heave is not covered by home insurance. Earth movement generally is not covered. That includes landslides, sinkholes, mudslides, and earthquakes.
Hope that helps!
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