A house is only as strong as its foundation. But regardless of how well built your house is, poor soil conditions, changing seasons, and moisture in the soil around your house will stress your home's foundation by expansion and contraction of the soil.
Here are the major factors that can affect and damage your foundation:
Your house is a heavy structure. If the earth below the foundation is of different densities (stone in one area and soil in another, for example), the foundation can crack and settle unevenly. If you've noticed the floors creaking, windows and doors sticking, or you see water in your basement, it's possible that you've had movement in the foundation.
Heavy backfill such as clay can create a great deal of pressure on foundation walls, with its weight pushing on the sides of walls and causing them to buckle inward. When this happens, cracks will form on the top of the foundation before advancing to the bottom walls inside of the basement. Once you see the cracks, they've already broken through the entire wall. And foundation wall leaks may occur.
Freezing and thawing cycles destroy roads, sidewalks, and parking lots, and these same forces are at work underground and are attacking your basement. If you take a rigid structure such as a foundation and subject it to the continuous flexing and contracting of the earth, damage is inevitable. Temperature fluxes cause the soil, water, and air around your foundation walls to expand and contract throughout the year, causing flexing against the wall and resulting in cracking.
Bad news about water around your foundation:
Water can hurt your basement in three ways: when it's there, when it's not, and when it's both.
When water seeps into the ground around the foundation and builds up, it's called hydrostatic pressure. The higher the water column up against the foundation, the more weight and pressure it causes. This water expands and contracts drastically (and sometimes freezes) as the temperature changes, which continually adds and takes away pressure on your walls. As hydrostatic pressure increases, water will enter your basement any way it can, seeping through porous concrete and block wall foundations, working through cracks, seeping through the wall joint, and entering your basement. The swelling of the earth under your foundation will actually lift up your house!
When water dries out around your foundation, the house will settle down again. The pressure against your wall decreases dramatically and the soil shrinks. This expanding and shrinking creates lateral pressure on the basement walls that can create horizontal cracks across the midpoint of the wall and will weaken the walls.
In some cases, the soil is both wet in some areas around the foundation and dry in others. When this happens, pressure on your basement walls from the outside is unevenly distributed, forcing strain on some walls or sections of walls more than others and causing cracks.
Tree roots can greatly damage foundation walls. As they grow in size, they can swell against the foundation of a house, pushing against the walls. They can also work their way into cracks and gaps in the walls and move underneath the foundation, pushing upwards on the house and causing the house to settle poorly as the earth dries.
Tree roots on one side of the house will dry the earth on that side unevenly. A tree that is 12 inches (30.5 centimeters) in diameter and 30 feet (9.1 meters) tall can absorb about 150 gallons (567.8 liters) of water per day during midsummer. This means that there is water on one side adding pressure to the foundations and not on the other. When the ground is wet, water tends to travel along the paths of tree roots as well as passages created by digging animals, underground water pipes, and electrical lines. If these roots and tunnels lead to the foundation walls, water is being guided along directly to your basement walls.
One final factor that may damage your foundation walls is the vibrations in the earth from nearby traffic. If your house is located directly alongside a major roadway (especially one where large trucks travel frequently), the continual vibrations traveling through the earth from the road over many years will weaken your basement foundation walls and damage your home.
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