Deck footings: How low should you go?

Frost depth a key factor in structural design

Q: How do you determine the depth of the deck footings to assure you have gone below the frost line? I live in central New Jersey, and thought I've always heard that the frost line here was 18 inches. But from reading a few articles on decks, I've seen conflicting information. Do you have a reliable resource? --Frank G. A: As you can imagine, frost lines vary widely by region. Also, most codes require that your footings be an additional 12 inches below the frost-line depth, as an added precaution against rare deep-freezing conditions. So, your best bet is to simply call your local building department and ask. However, if you would like to try to figure it out yourself, there is a good booklet available for free from the Department of Housing and Urban Development (HUD). Go to In the search box, enter "Structural Design Loads for One- and Two-Family Dwellings," which will take you to the booklet. It's about 50 pages, in PDF format, so you can re...