Common foundation material:
Poured concrete foundation Concrete blocks foundations
In building today there are basically three types of foundations:
Basement Crawlspace Slab
- Settlement cracks. Settlement cracks are caused when the footing supporting the home moves downward or tips. Foundation settlement and movement can be caused by building on expansive clay, compressible or improperly compacted fill soils, or improper maintenance around foundations. In any case, water is the basic culprit in the vast majority of expansive soil problems. Specific constituents of certain soils tend to swell or shrink with variations in moisture. The extent of this movement varies from soil to soil. When unstable soils are used as a base for a foundation, the tendency for movement is transmitted to the foundation. Since soil movement is rarely uniform, the foundation is subjected to a differential or upheaval.
- Concrete shrinkage cracks. Shrinkage cracks in concrete occur only during curing. Concrete shrinkage cracks are not usually a structural problem but may permit water leaks through the foundation wall.
- Cold joints.
Cold joints in concrete foundations which leave visible lines in the concrete foundation wall are not usually a structural problem but may in some cases form a dry joint which permits water leakage through the foundation wall. Cold pour joints occur because of the time delay between subsequent "pours" into the foundation forms.
- Holes and penetrations. Holes and penetrations in concrete foundations such as poorly-sealed openings left for piping for water or electrical lines or where form ties were broken off may form points of water entry into the structure but are not normally a structural concern.
- Vertical cracks. Vertical cracks can be caused by simple shrinkage of materials. These cracks often occur in the control joints of poured walls. Some vertical shrinkage cracks in poured concrete can be up to 1/8 inch wide. Vertical cracks are an issue if they are wide, tapered from top to bottom, or found in combination with other cracks. They can occur because of settlement, wall movement or tipping walls. Vertical cracks also occur if a wall is pushed in and breaks away from the adjacent corner or surface. Vertical cracks with horizontal or shear movement at the crack always indicate a problem.
- Horizontal cracks. They indicate that the wall is displaced horizontally. As the wall is pushed in, the joint opens up inside the basement and a similar crack will occur outside
near the base of the wall. Horizontal cracks are caused by wet soils, poor maintenance of surface water and frost. Horizontal
cracks often will change seasonally. When there is water in the soil, the soil may expand — a common trait of clay soils. When the wet soil expands, the wall may be pushed in and the horizontal crack may open further. When the soil dries, the crack may close. Frost in exterior soil causes similar movement and cracking as the frost expands the soil.
- Horizontal cracks – horizontal cracks are most serious, and indicate that water-saturated
soil outside froze and expanded, pushing in and breaking the foundation. Perhaps gutters backed up and heat was off for an extendedperiod during especially cold weather. Horizontal cracks also occur because of problems with underlying soil. If you have soil that expands when damp and shrinks when dry, you face the same range of solutions as if you had a slab foundation.
- Step cracks. Step cracks refer to cracks that follow the mortar joints in a block wall. The cracks step up or down along the mortar. In many cases, this type of crack is caused by minor movement of the footing, shrinkage or wall movement, and by itself is not a major cause for concern; however, wide cracks or step cracks combined with other cracks and movement indicate a problem. Step cracks often will occur at the weak point of a wall—around window openings. Step cracks are common at “beam-end” walls. At the beam-end wall, the beam transfers a large point load to the wall. The load often creates step cracks down and away from the beam as the footing settles ever so slightly. Block walls do not like to move; they do like to crack. A vertical crack also may occur at the beam end wall, below the beam.
- Rafters overspanned or undersized.
- Too many layers of roof materials.
- Excesive loads (snow drift, roof - mounted equipment).
- Removal of collar ties or other intermediate supports.
- Ineffective or missing intermediate supports (collar ties, ridge pist, purlins, knee walls).
- Poor rafters end bearings.
- Rafters slips freerly past walls.
- Weak connections.
- Walls pushed out with rafters.
Uneven, sloping or sagging floors can be caused by:
- Bulging or loose floor planks (that has been used for sub-flooring) and hardwood floor.
- Saging or rowning floor joists and beams.
- Joists overlapping beams too far – joists ends too long causing end to raise up when joists deflects.
- Deteriorating beams supports (posts and fotting).
- Deteriorated, rotted sill (sole) plates.
- Non uniform foundation and posts (beams support) settlement.
- Floor joists and beams cracked, undersized or overspanned.
- Many structural problems in a house come from differential settlement. This type of settlement occurs when a portion of your home is sinking into the ground faster than other parts of the home. This puts great stress on the foundation, walls, floors, ceilings, and the roof. The entire structure can be compromised by these settlement situations. Settlement can also cause damage to water and gas pipes.
- All houses settle to some degree in the first few years that they are built. Settlement is the norm for all houses ever built. Settlement shows itself if through cracking in the structure. When looking at your foundation cracks that are uniform and go from the top of wall to bottom of wall are of less concern then the cracks that run horizontal. Horizontal cracking can lead to bowing of foundation walls and if it gets bad enough walls above can begin to tip. Tipping walls can eventually work off of the foundation and create total structural failure. Another deadly crack is he dreaded V shaped crack in a foundation
- Inadequate grading – if the ground around a foundation is level or slopes toward the house, water
is directed into the basement. The soil next to the house is often backfilled without proper compaction and later settles. This is especially true under stoops where water can collect next to the basement wall.
- Defective/missing gutters and downspouts. Missing gutters and downspouts cause rainwater to be
directed toward the foundation perimeter. A downspout without an extender or splash block is worse than no downspout at all. It is depositing the huge volume of rainwater from the roof in a single concentrated location near the basement.
- Ineffective/missing drain tile sump pump and pit. Many existing houses simply have no subsurface
drainage system. This comes from a time when basements were not used as habitable space. In other cases, the systems do not work for a variety of reasons, such as collapse of the pipe, clogging of the pipe with silt and/or tree roots, or a broken connection to the sump. The sump pit usually contains a pump designed to lift the water to the ground surface outside the foundation wall. This pump can fail.
- Structural cracks. Most basements and crawlspaces (concrete and concrete block foundations) show some signs of leaking and cracking. Through the years, problems with water, poor soils, grading, drainage and possible settling affect the integrity of a basement.
- Improperly designed window wells. Window wells are like a drain right next to the basement wall. Often they are improperly built so that any water is directed toward, rather than away from the foundation.
- Missing vapor barrier. An adequate vapor barrier will create a dry air space between the damp soil and the framing, which will limit the amount of moisture that is able to rise into the framing (dampness in the crawl space area creates decay and deterioration of framing members). This also reduces the possibility of future moisture damage.