In Carroll County and the rest of Southwest Virginia's Blue Ridge foothills, footings for walls, chimneys, and additions typically need to sit somewhere in the 18 to 24 inch range below finished grade to get below the local frost line, though the exact depth your permit requires depends on your site's elevation and soil conditions. A footing that's too shallow sits inside the zone that freezes and thaws every winter, and frost heave will eventually crack or lift it.
The frost line is the depth soil moisture reliably freezes to in a given winter. Below that depth, the ground stays a fairly steady temperature year-round and doesn't heave. A footing poured above the frost line sits in ground that freezes and expands every winter, and that expansion pushes on the footing unevenly, which is exactly what causes the cracking and lifting frost heave is known for. Getting the footing below that line is the single biggest thing that prevents it, and it's the first question any competent contractor should be answering before a shovel goes in the ground.
The exact number isn't the same everywhere in the region. Higher elevation sites generally see a deeper frost penetration than a sheltered valley lot, and soil type matters too, since clay-heavy soil holds more water and heaves harder than well-drained, sandy soil at the same depth. The local building department sets the specific requirement for a permit, and it's worth confirming rather than assuming a number that worked on a different job or a different county applies here, since a depth that passed inspection somewhere else isn't automatically what Carroll County requires.
Chelo's pulls the required permit and digs to the depth the county requires, on undisturbed soil rather than fill that hasn't fully compacted. Skipping that step to save time on a job is exactly how a wall or chimney ends up with cracking and settling problems a few winters later, and it's not something that gets fixed cheaply once the structure is built on top of it. Doing it right the first time, at the correct depth on solid ground, costs far less over the life of the structure than digging it back up later.
More on this from Chelo's Brick & Stone.
Chelo's Brick & Stone serves Hillsville, Galax, Wytheville, Fancy Gap, and Independence, VA. Call for a straight answer and a free on-site estimate.
