"Why is the basement floor all cracked? Is the house shifting?" This seems to be a very common question these days. By my count, nearly 25% of homes have basement floors which are heaving, cracking or breaking up. This percentage is much higher in some areas, such as river Heights. However, before we hit the panic button, or discount a potential home, lets take a look at what is really happening:
It is important to understand how homes are constructed. After the hole is dug, the 'footings' are poured in place.
These footings are concrete and typically 16" to 24" wide by approx. 10" thick. They basically follow the outline of the house (not including the garage). In addition, you will find 3 or 4 square concrete blocks in the centre of the outline, which will hold future teleposts. These footings serve to hold the weight of the house. The next step in the constrution process is to pour the basement walls into these footings. Following this, the entire house is built, up to and including the roof. The last thing in the project is to pour the concrete basement floor. This is poured on top of the footings, and not attached to them. This is to allow the basement floor to float, much like a driveway. The reason for this is simple: As the ground underneath the house shifts and settles, it creates very high forces. The 24" wide footings are able to deflect those forces sideways, however a large slab of concrete, perhaps 1400 sq ft in size, would not be able to deflect this force, and must be allowed to move up or down.
What about piles? A common mis-conception is that piles would prevent this from happening. It is important to realize that the piles sit under the foundation (and footings) only, and have no impact on the basement floor. An average home may take 20 or more piles, just to secure the foundation.
So if you see a house which has a rough and uneven basement floor, this does not mean it will ever affect the structure. On the other hand, a pristine basement floor does not mean it will never shift or get worse, either.
The bottom line: The basement floor does not form part of the structure of the house, and is designed to move and shift with the Manitoba Gumbo.