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This article continues our discussion of the the causes of foundation cracks, buckling, or collapse in areas of freezing weather, clay soils, or wet soils. Here we explain the difference between the vertical lift of frost heaves and ice lensing (or frost lenses) and we include details of the construction of a frost-lens-proof structural pier, and we provide data on the amount of soil pressure and expansion exerted by water and freezing. In this article series we include solar energy, solar heating, solar hot water, and related building energy efficiency improvement articles reprinted/adapted/excerpted with permission from Solar Age Magazine - editor Steven Bliss. Photo (above) shows a crew constructing a structural pier (in clay soils) that successfully resists ice lens lifting in Minnesota.

Readers who need to diagnose the cause and decide on the cure for foundation damage should start at FOUNDATION CRACKS & DAMAGE GUIDE. Readers should also see BASEMENT HEAT LOSS for a discussion of basement and foundation insulation. Contact us to suggest text changes and additions and, if you wish, to receive online listing and credit for that contribution.

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Frost Heaves Compared with Frozen Soil Impacts on Foundations

There are two distinct problems associated with frozen ground and its effects on building foundations: frost heaving and pressures from frozen soils.

Details About Ice Lenses in Soils

Frost heaving is what makes roads buckle during the winter in many northern states and provinces. It is caused by small plates of ice called ice lenses that form a foot or more below the surface. Ice lenses draw water from surrounding soil by capillary action, typically growing up to 1/4 inch to 2 inches in thickness and up to several feet across.

Often frost lenses form in multiple layers, adding to the total soil movement in an upwards direction. Ice lenses form in porous silts and also in clays that can support capillary action. They need extreme cold, combined with a subsurface water source - that water might come from ground water, surface runoff, or even roof runoff around a building. Roads and sidewalks are good candidates for frost heaves because melted snow provides a good water source as well, and frost can penetrate deeply into the soil because roads and sidewalks are cleared of their insulating snow cover.

Where the direction of heat loss is upwards to grade, ice lenses form horizontally. In these cases, ice lenses push mostly upward, not laterally. Theoretically, a frost heave could lift a building foundation wall or a pier if the soil above the ice lens were frozen to and adhered to the foundation wall or pier surface.

Healy has seen concrete piers for highway sign posts lifted as much as an inch per year by frost heaving, but he has never seen frost do structural damage to foundations. Where the direction of heat loss is horizontal, as through a retaining wall or the wall of a frozen basement, ice lenses could form in the vertical plane and push laterally.

Constructing a Frost-Lens-Push-Proof Stage for Summerblue Arts Camp in Two Harbors, Minnesota

Indeed frost lenses or ice lenses can lift a building foundation by adhesion to the foundation sides, especially at a a building corner. We (DJF) observed this condition at a 1960's home in Poughkeepsie, NY, where a building corner was lifted each winter by freezing wet ground. Even though the wall's footings were below the frost level, ice lensing against the top few feet of the buried portion of the foundation wall was causing an annual movement problem that cracked the masonry blocks in a stair-step pattern at the building corner, and cracked the drywall in the bedroom above. The owner dug at the problem corner, found a ground water source, a spring, and cured by installing drainage to remove the water problem.

Soil frozen against a foundation wall or a pier, or ice lenses where there is a lot of ground water, can also pinch and lift piers and posts. When Lon Church, director of Summer Blue Arts Camp in Two Harbors, Minnesota, decided in 2001 to construct an outdoor stage platform that would be exposed to both clay soils and very cold weather, we wrapped the platform's piers in several layers of 6-mil polyethylene plastic to reduce the ice grip around each pier, thereby reducing the ability of ice lenses in the freezing soil to lift the piers supporting the stage.

In our deck construction photos (see the center post in both photos above) you can see that we brought the poly well above ground level during construction. Here is a closeup of the frost lensing protection installed during pier installation. In our "Summerblue Arts Camp" winter photo (above right) you can see the same pier, still protected by plastic. Eight years after construction (in 2009), and after a number of very cold Minnesota winters, we had seen no frost movement in the piers for this outdoor stage. -- DJF.

How Much Does Wet, Frozen Soil Expand to Cause Pressure & Damage to Foundations?

Our photo (below) shows excavation and a new foundation under a home that suffered a catastrophic foundation collapse. The foundation wall in the right of this photo collapsed inwards into the garage, due to pressure from water-soaked earth that was caused, in turn, by surface runoff from a hill that sloped directly towards the home's rear wall. -- DJF

Soil that expands due to freezing is a separate problem from frost heaves or frost lensing. The necessary ingredients are water-saturated (often clay-containing) soil and continuous freezing temperatures. Water-saturated soils, where clay is involved, can hold up to two-thirds water by volume, and water expands by 8 percent when it freezes. So the total volume of soil can expand by as much as 5 percent during freezing conditions.

Unlike ice lenses, this freezing soil expansion exerts force in all directions. The force exerted by freezing soil against a foundation wall, according to Heley, could be enough to crack the un reinforced walls in Duluth, and we confirm that this phenomenon can occur even further south, to the limits of areas of freezing soils.

Even if the foundation wall does not cave in, the expanding mass of freezing soil may make a mess of exterior insulation or waterproofing coatings, as was reported in Fargo. As the soil expands, it may drag the exterior insulation or waterproofing foundation membrane with it. For this reason, some builders drape a loose layer of polyethylene plastic over their waterproofing or exterior insulation to act as a slip joint, such as we described for the outdoor stage piers. Others, like Heley, put foundation insulation on the interior.

Use links just below or at the left of each page to navigate this document or to view other topics at this website. Green links show where you are in our document or website.

  BUCKLED FOUNDATIONS due to INSULATION?
    Insulation's Role in Foundation Damage
    Foundation Damage Generally Involves Water
    Ice Lenses, Frost Heaves vs. Frozen Soil Pressure
    Frost-Lens-Push-Proof Structural Pier
    Wet, Frozen Soil Expansion Data
    Main Cause of Foundation Failures in Clay Soils
    How Avoid Foundation Cave-Ins

Here we include solar energy, solar heating, solar hot water, and related building energy efficiency improvement articles reprinted/adapted/excerpted with permission from Solar Age Magazine - editor Steven Bliss.

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• Solar Age Magazine was the official publication of the American Solar Energy Society. The contemporary solar energy magazine associated with the Society is Solar Today. "Established in 1954, the nonprofit American Solar Energy Society (ASES) is the nation's leading association of solar professionals & advocates. Our mission is to inspire an era of energy innovation and speed the transition to a sustainable energy economy. We advance education, research and policy. Leading for more than 50 years. ASES leads national efforts to increase the use of solar energy, energy efficiency and other sustainable technologies in the U.S. We publish the award-winning SOLAR TODAY magazine, organize and present the ASES National Solar Conference and lead the ASES National Solar Tour – the largest grassroots solar event in the world."
  
• Steven Bliss served as editorial director and co-publisher of The Journal of Light Construction for 16 years and previously as building technology editor for Progressive Builder and Solar Age magazines. He worked in the building trades as a carpenter and design/build contractor for more than ten years and holds a masters degree from the Harvard Graduate School of Education. Excerpts from his recent book, Best Practices Guide to Residential Construction, Wiley (November 18, 2005) ISBN-10: 0471648361, ISBN-13: 978-0471648369, appear throughout this website, with permission and courtesy of Wiley & Sons. Best Practices Guide is available from the publisher, J. Wiley & Sons, and also at Amazon.com.
  Excerpts with updates and annotations expanding the original Best Practices Guide text can be found in the online review and book summary at BEST CONSTRUCTION PRACTICES GUIDE and also at DECK & PORCH CONSTRUCTION, at INDOOR AIR QUALITY IMPROVEMENT GUIDE, and in other articles found at InspectAPedia.com such as HOUSEWRAP AIR & VAPOR BARRIERS, SOUND CONTROL in BUILDINGS, and other topics.

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