Footings serve as a foundation for decks because they support the posts that hold up the deck flooring. A deck can slowly sink into the soil or show damage after a significant shift in the ground when footings fail due to improper installation. The proper spacing of footings helps ensure that a deck holds up under various amounts of weight.
There are several types of deck footings, and the type you need to install is dictated by local building codes. In any case, the spacing between footings depends on the size and shape of the deck and the number of posts the footings need to support. The heavier a deck is, the more footings it usually needs to prevent the structure from collapsing. Decks with hot tubs, for example, usually have footings placed close together to evenly distribute the amount of weight that each footing carries.
Footings are generally spaced up to 8 feet apart, according to "Professional Deck Builder" magazine. Yet deck designs may show footings placed farther apart. Sometimes designers reduce the number of footings by increasing their size so that each footing can carry more weight. Using engineered beams to support the deck flooring also helps reduce the number of required footings. The beams consist of several layers of material that are stronger than a single wood board. However, adding larger footings and engineered beams to a deck design may increase construction costs.
The spacing of the footings is critical even for simple, rectangular decks, because the footings may need to bear weights exceeding a ton. For example, "Fine Homebuilding" magazine outlined the steps followed to construct a 192-square-foot deck. The builder determined that four footings needed to bear a total of 4,800 pounds. The footings were placed 64 inches apart to handle the load.
Consult with a contractor or structural engineer to determine the spacing for footings if you intend to build or design your own deck. Some companies provide ready-made deck plans for do-it-yourselfers. However, the spacing for the footings on such plans would need to be changed if you alter the design. Local climate conditions also affect deck construction. For example, decks in areas that get heavy snowfall need to have properly spaced footings to bear potentially large snow loads.