Every municipality has what are known as design criteria for their region. These criteria include things like wind speeds, snow loads, what kind of seismic activity can be anticipated, and that sort of really useful data.
One of these criteria is the frost depth. Also known as the frost line or freezing depth, it is the point in the soil where groundwater can reasonably be expected to freeze.
This is important to the home builder because the foundation can be damaged by frost heaves. These occur when the water freezes into ice crystals. Remember that water expands when it freezes? It is that same basic fact with the added concern that it is applying force to the foundation and can crack a foundation wall.
Older homes in our area often do not have sufficient depth on the foundations. Short of major excavation and rebuilding of the foundation, this is not correctable.
On newer houses, it should never be an issue - until it is. I ran into that recently in a house that was built after 2000. I popped the hatch, saw this -
- and ran for my tape measure. By measuring the distance from the base of a window to the bottom of the foundation wall, both inside and out, I determined that the depth was 27 inches.
Design criteria for Whitman County is 32 inches.
Houston, we have ourselves a problem. Add in the fact that the home was two stories tall over this, and the problem compounds.
My recommendation to my client was to seek professional engineering. Not good news for them, I know, but better to know these things on the way in than six years from now.