04 Nov What Causes Heaving in a Basement Floor?

When you observe cracks in your basement, it’s common to think that your house might be settling. However, whereas settlement occurs when a house or parts of it sink into weak soil, heaving occurs when the soil underneath the basement expands and pushes the floors upward. That is, settling results in sinking floors while heaving leads to parts of the floor, typically the middle of the basement, rising or being higher than the edges.

Soil underneath the basement can expand due to changes in ground moisture levels, which can be caused by various factors.  Here are some of the most common causes of heaving in a basement floor.

Expansive Soils

If you live in an area with soils rich in clay, then your basement might be prone to heaving. You see, clay can absorb water after heavy rain or floods, which makes it prone to swelling. Excess water saturates the soil, expanding it significantly, which in turn, creates the immense upward pressure that results in heaving.

In fact, this issue may start as early as during the excavation of the house’s foundation. Excavation gives the clay-rich soil a chance to dry out and shrink. However, once the house is built and rain falls, the soil becomes like a sponge that absorbs tons of water. This excess moisture exerts pressure on the basement floors and the foundation walls.

Clay can also really dry out and shrink during dry periods. So, there is a cycle of contraction and expansion in the soil, which can lead not only to heaving but also to uneven settlement over time.

Hydrostatic Pressure

Hydrostatic pressure is the push or force exerted by a stationary or standing liquid like water at a given point due to gravity. This force is equal in all directions and is caused by the weight of the fluid above it, which means the pressure increases with depth. We experience this when our ears pop every time we go swimming in deep waters.

In infrastructure, engineers and other builders account for hydrostatic pressure into their designs. For instance, dams are built to have a wider or thicker base to withstand stronger hydrostatic pressure pushing against the bottom of the structure.

In your house, hydrostatic pressure comes in the form of rising groundwater levels due to poor exterior drainage or the wet season, which pushes water up against or beneath your basement’s concrete slab. In other words, when water builds up, say around the outside of your foundation, it increases the pressure along the walls and floor in your basement. Hydrostatic pressure can exceed the weight of the concrete in your walls and floor and lead to cracks and heaving.

Plumbing Leaks

Another cause of basement heaving are broken or leaking underground water and sewer lines, especially those plumbing lines that run through a foundation or underneath a concrete slab in your basement floor. These plumbing leaks can saturate the soil and cause it to swell. The result: heaving of your basement floors.

Under-slab leaks can be harder to pinpoint and can go unnoticed from a few weeks to several years, depending on the path and size of the leak. While you might observe the signs of large leaks, small or minor leaks can slowly disperse water beneath the concrete indefinitely, as they don’t come with tell-tale signs that you would be able to see immediately.

Frost Heave

During winter and early spring, freezing temperatures turn the water in the soil to ice. When water freezes, its volume increases by around 9% and results in the expansion of the soil. As this ice expands, it pushes upwards against your basement floor, sometimes by several inches or more.

The pressure exerted by the expanding ice leads to cracks and shifts in the basement floor and foundation. Frost heave is a typical problem if you live in an area with moisture-rich soil, or in the case of foundations, if these were built above the freezing line.

Major Signs of Basement Floor Heaving

When you’re having issues with heaving in your basement floor, these are typically the signs you should watch out for:

Uneven Floors

Look for indications that the floor has moved upward, for instance, slopes, bulges, or uplifts. It is common for the basement floor to look humped or raised compared to the edges. These are clear signs that the ground beneath your basement floor has shifted. Uneven floors are especially noticeable in concrete or tile floors.

Cracks

Another sign to watch out for are cracks in walls, ceilings, or floors. Especially look for vertical or diagonal cracks near windows, doors, or corners or where the walls meet the floor. These are often the first visible symptoms of heaving.

Sticky Doors and Windows

If you notice that your doors or windows in the basement have become difficult to open or close or jam more frequently during cold seasons, then you might have a heaving problem. Sticking doors and windows can be the result of a foundation heave.

Floor and Ceiling Gaps

Gaps between the walls and floors or ceilings might also form because of heaving. These parts can get twisted out of alignment because of the uneven lifting of sections of the basement.

How to Fix Heaving in Your Basement Floor

Repairing basement floor heaving is a two-step process. First, you’ll need to fix the root cause and then choose a repair method.

Step 1: Eliminate the Root Cause

Before doing any repair job on your basement, it’s best to first take care of what’s causing the problems in the first place.

• Check the plumbing for any water leaks, especially those hidden beneath the concrete in your basement.
• Inspect the foundation grading of your home. Ensure that the ground slopes away from the house and that gutters are at least 5 to 10 feet away from the foundation.
• Relieve hydrostatic pressure by installing a sump pump or interior perimeter drainage system.

Step 2: Repair the Damage

Once you’ve fixed the root cause of your basement heaving problem, you can move on to deciding the repair method to use for the damages.

• Grinding can be used to smooth out uneven transitions or high spots for minor heaving issues of under 2 inches.
• Crack stitching and resurfacing uses a structural epoxy or a hybrid patching material to seal minor cracks.
• Slab replacement can be performed for severe heaving (over 2 to 3 inches) or to fix a shattered floor.

Note, however, that while you can fix hairline cracks easily, basement floor buckling or lifting requires the immediate attention of an expert. Professionals will conduct an inspection or evaluation and help you root out the cause and guide you on the appropriate repair method to use.