In rare cases a concrete slab foundation will fail.
Most often it is the floating slab floor of a ranch that settles.
What we see most commonly is that a corner of a room settles and the rest of the structure remains intact.
Usually this is due to bad drainage, ground movement, subsidence or poor construction.
The problem will usually be noticed when doors that used to open and close start sticking, or a gap appears between the skirting board and the floor/carpet.
You will notice
That the floor has a slight slope.
A gap may be visible at the baseboards that is greater on one end of the room than the other.
The baseboards have been installed at a sloping angle or quarter round added in a room that has carpet.
A door may be catching in the frame.
If you pull back the carpet there will be a good size crack that is probably uneven.
These types of foundation problem can be repaired.
First of all, any drainage or water problems need to be addressed.
Water that flows toward the house or tends to pool near the building because of poor grading needs to be addressed.
Re-doing the grading to keep water away from the area surrounding the house would be the first line of defense.
If is not possible to change the grading, a perimeter french drain (underground) could be installed that pipes the water away.
Downspouts will need to be piped away, a minimum of 8 ft from the foundation.
A concrete leveling company that can “mud jack” or lift the slab will need to be hired.
They can usually repair the foundation in one day without too much disturbance to your home.
The work to raise the slab involves lifting the carpets and drilling one or more small holes through the foundation slab, through which a concrete or crushed stone slurry is pumped into the area under the slab which lifts it returning it to its original position..
A special concrete or slurry mix under pressure is then pumped into the area under the slab. Raising it and returning it to its original position. In cases where the ground under a portion of the building is unstable and “mud jacking” alone may not be adequate, piers can be sunk. These piers are then attached to a bracket mounted along the outside edge of the foundation’s slab. This holds the building in place, giving it the rigidity and structural integrity necessary.