There are no perfect houses and that would include their foundations. Whether you have a new house or one that is a hundred years old, the foundations of houses crack. The houses change and settle after construction. Homes will have cracks in cosmetic finishes or structural components. Most of these cracks have no structural significance. Common types of cracks in foundation walls will include;
Vertical (or almost vertical) cracks; Just because a wall has cracked does not mean it has failed or that corrective action is required. If the crack is narrow (1/8 inch or less), is nearly vertical, has no lateral separation between adjoining portions of the wall, and no water seeps through the crack, no action is generally required. This is a shrinkage crack and occurs when the moisture in the wall evaporates, causing the wall to shrink into the voids created by escaping water. These types of cracks are controlled, or minimized, but not eliminated, by the use of horizontal reinforcing steel, which helps distribute stresses in the wall. If horizontal steel is present, it is more likely to have several very small cracks rather than one or two much wider cracks. Another method of limiting shrinkage cracks is to control the amount of water used in the concrete mix.
reentrant cracks; Whenever a concrete member has an acute angle, there is a stress concentration. This almost always results in a crack called a re-entrant crack emanating from the inside corner. It can be vertical, horizontal or diagonal when leaving the corner. This phenomenon exists in almost all materials. Round openings can dissipate stress, but this is not practical in concrete wall construction. The typical remedy to reduce this type of cracking is the placement of steel reinforcement in the corners. It won’t eliminate these cracks, but it will keep them tight and controlled.
Horizontal cracks; Horizontal cracks require more scrutiny. Most residential foundation walls are designed to span from the base or floor slab to the connection of the upper story structure. An 8-inch concrete wall in normal soil conditions is generally strong enough to support the forces exerted on the wall without vertical reinforcement. Exceptions include areas with high groundwater conditions or in expansive soil conditions. If there is vertical reinforcement in the wall, a horizontal crack is probably not a concern. An expert should be consulted when a horizontal crack appears to assess whether there is a structural risk.
These cracks generally result from one or more of the following;
1. Settling of the soil below the foundation results in downward movement of the foundation and displacement is common in most newly built homes.
2. Alteration of the local water table each time a new house is built. Specifically, the soil under the house dries out; the resulting soil shrinkage causes minor settlement of the footing, which can cause very little cracking in the foundation walls.
3. A new house, without furniture or effects, does not impose a significant load on the foundation. Once all of your furniture and appliances have been moved, the weight on the foundation and overall structure increases and causes some flexing (or movement) of structural members throughout the building. This increased load can cause hairline cracks in the foundation.
4. Drying shrinkage. As poured concrete dries and hardens, it will shrink. The main factor influencing drying shrinkage is the total water content of the concrete. As the water content in poured concrete increases, the amount of shrinkage increases. Significant increases in sand content and significant reductions in the size of the coarse aggregate used in poured concrete increase shrinkage because the total water content increases and the smaller size coarse aggregate provides less internal shrinkage strength.
5. Thermal expansion and contraction of concrete. Concrete poured during high daytime temperatures will shrink as it cools overnight, which may be enough to cause cracking if the concrete is contained.
6. Restricts; The restriction of the free movement of fresh or hardened concrete after the completion of placement (concrete pouring) in the formwork or within a confined space; The constraint can be internal or external and can act in one or more directions.
7. Subgrade settlement or movement. The detachment of the soil or the footing due to its mass, the loads imposed on them, or the contraction or displacement of the underlying support.
Most foundation cracks are minor and insignificant; are common to poured concrete and block foundations. Structural (horizontal) cracks in residential foundations are usually the result of settlement and/or horizontal loading. They can be the result of hydrostatic pressure or the use of heavy equipment next to the foundation. The possible implication of foundation cracks is moisture penetration, moisture that can ruin wall coverings, floor coverings, and finished furniture.
Water will seep through a crack in the foundation if there is enough hydrostatic pressure to force the water through the crack. If a waterproofing system was installed during construction, the basement may not leak even if there is a large crack. Keep in mind that waterproofing is not the same as waterproofing. Installing an exterior waterproofing system after the wall has been backfilled can be cost prohibitive. The best solution is the use of an epoxy injection system. It will stick to the side of the cracks and can actually make the wall stronger. These systems can be DIY, but it is highly recommended that they be applied by a professional.
If you take something from this article… take this. All foundations crack, your foundation, my foundation and most of these cracks are insignificant and have no structural implications. If you are in any doubt about the size and type of the crack, call a professional for evaluation.