First, what is slab clearance?
Slab clearance is the amount of exposed concrete between the ground and the first layer of mortar as shown in the photo above. What we like to see is around 6-inches of slab clearance. More is better, but even a couple of inches is better than nothing.
Does inadequate slab clearance hurt foundation performance?
Strictly speaking, slab clearance has no relation to foundation performance. There are two advantages to slab clearance.
The wood framing, specifically the bottom plate, is subjected to more moisture as it gets closer to the ground. As the wood in the wall absorbs moisture, the wood frame begins to rot. Unfortunately, subterranean termites will inevitably be attracted to the soft rotted wood.
One way termites can gain access to the wood frame structure is to build a tunnel that extends from the ground to the top of the exposed slab. If there is good slab clearance, the tunnel will be easily seen. If someone sees the tunnel, corrective action can be taken before the termite damage becomes widespread.
How can inadequate slab clearance be corrected?
First, upon discovering an exposed tunnel, you should contact a licensed structural pest control operator. A licensed pest control operator can determine if the infestation is active.
Next, you have to remove soil, mulch, compost or anything else that obstructs seeing the concrete.
Don’t make this mistake.
This mistake is pretty common. When the soil is removed the result may be that there is a small ditch adjacent to the perimeter grade beam. That shallow ditch prevents water from draining directly away from the foundation. One problem has been exchanged for another problem.