How Frost Heaving and Ice Lenses Causes Structural Damage to Homes
A homes’ footings are normally required to be below the frost line to prevent structural damage to the foundation or basement walls. Frost heaving, ice lenses and the failure to have footings below the frost line may result in costly structural problems.
Building codes generally require that a homes footings, piers or piles meet frost line depth requirements to avoid frost heaving, however, these codes are minimum requirements and may be insufficient to prevent damage from frost heaving and ice lenses. Additionally, plumbing codes address depth of sewer and water lines so that they will not likewise be damaged by freezing temperatures.
The frost line depth is basically where water (moisture) in soil will not freeze and varies greatly in the continental US.
Frost Line depth of freezing may range from 0 inches in Southern Florida to over 8 feet in Northern Maine
Map of FROST LINE depth shown in inches
When footings are not deep enough and the soil under them freezes, there may be tremendous up-ward forces that will lift and damage a home’s foundation.
Frost Heaving and Ice Lenses Damage Footings, Foundation Walls, Slabs and Piers
Water in soil and below-freezing temperatures is what causes frost heaving that cracks and damages foundations, concrete slabs and basement walls. Tremendous pressure builds up when wet soil freezes for several reasons. One reason is that water expands about 9% when it freezes, and this increase in volume exerts an upward force on foundations and piers, as well as lateral pressures on basement and foundation walls.
Areas with freezing temperatures, especially areas that have high water tables or lots of rain and temperature changes can create conditions with additional issues that result in more damage to a home’s foundation, foundation walls and basements. Concrete slabs may also experience cracking and damage due to these environmental factors.
Homes constructed on or using concrete piers may suffer damage.
Hillside homes will often use a combination of foundation systems, one of which may be concrete or wooden piers. The same forces that affect other types of foundations will also affect concrete piers.
What are ice lenses?
You might think of Ice lenses as long ice crystal formations formed by layers of ice within the ground whose size will be based on the amount of water available and the frost susceptibility of the soil type.
The lifting force of one or more growing ice lenses may be enough to lift a layer of soil as much as 3 to 12 inches or even more in extreme cases.
Soils freeze from the top down
As soil freezes, it starts at ground level or the top layer of soil. This top layer expands both width wise and depth wise as it freezes and may lock a foundation in place.
As the depth of freezing goes lowers, it forms another layer (or ice lens) which likewise expands and pushes up-ward on the top frozen layer; this upward and outward pressure exerts more force on the foundation and / or basement walls.
As long as there is moisture available and freezing temperatures, this process repeats itself. Additional, water may migrate from lower areas upward, even 5 or 10 feet below, through a process called capillary action.
When a foundation is pushed up by the force of the ice lenses it often creates a gap or space under parts of the foundation; then as the soil warms, the foundation drops down, but not fully down. This shifting of the soil can result in un-level, tilting, cracked or damaged foundations.
Basement walls may tilt, bow inwardly or crack but will seldom shift back to their original or straight position when the soil warms.
Types of soil play a role in the severity of damage
The type of soils will have a direct bearing on the severity of damage. Soils that are expansive in nature, like silty or clayey types of soils or ones that hold large amounts of water usually increase the severity of damage. Another issue that may increase damage are soils that were not originally compacted properly; often found in areas next to basement walls.
Over the seasons and years continual freezing and thawing causes more and more damage
When soil freezes, it often expands and puts pressure against a home’s foundation and basement walls, often causing cracks and damage. Then it thaws, and more movement of the soil occurs, including settlement.
Not all areas of a foundation or basement walls experience the same amount of heaving, settling and lateral pressures; therefore, some areas will experience more damage than other areas.
This factor may also cause differential settlement, which is the worst type of settlement for a home’s foundation or slab. ( Read about differential settlement )
How to reduce damage from frost heaving and ice lenses
If building a new home
If you are going to build a new home in an area where soils are going to be subject to moisture and freezing conditions, be sure to discuss with the engineer and builder your concern about soil issues and request that they review the plans to ensure that you will not face serious issues.
If living in an existing home
Reducing the amount of water penetrating the soil near a home’s foundation will often help reduce damage. Naturally, the first thing to look at would be the over-all drainage around the home, for the less water that gets near the foundation, the less potential for damage.
Consult a foundation engineer or specialist
Professionals can often provide a homeowner with an analysis of any existing problems and provide ideas and options on what you can do to resolve, reduce or prevent frost damage issues.
The more a home moves or shifts, the more damage it will incur. Damage may occur to a home’s foundation, concrete slab, basement walls (if any) and to the structure that sits on top of the foundation.
Damage may include cracked and un-level foundations, cracked slabs, cracked and leaking basement walls, bowed or tilted foundations or basement walls; and frost heaving may even telescope into damage to drywall, roofs, sloping floors or doors and windows sticking.
Water issues, drainage, soil types and freezing temperatures all play an important role in frost heaving and ice lenses.