The larger the beam and footing size the fewer footings that are required. For most situations you will want to place footings and posts less than 8' apart. If you are planning on installing a hot tub or porch on top of your deck you will usually need more footings and posts to support the additional loads. Decks with lots of angles may also require additional footings. You may be able to reduce the number of footings if you use an engineered beam and increase the size of your footings. This will also increase the costs of construction. You can begin to answer your own question by using our footing and beam calculator.
It is very important to build the deck footings in the right locations. There are two principle methods for accurately laying out the footing locations based on your plans. It usually helps to have the ledger board installed to give you two fixed positions at the house to work off of. Remember that the dimensions on your plan are drawn in two dimensions. You must keep your lines or tapes level in order to avoid distorting the shape of the deck in three dimensional space. Laying out footings is usually a two-person job. You will need an open space to work in, you must move anything that will interfere with your lines or tapes in the site area.
Batter Boards - This method is the most commonly used; you will need a cloth tape measurer, some wooden stakes, and a roll of twine. Drop a plum bob from the corners of your ledger board and set two stakes next to the house. You can start here in order to layout the perimeter of your deck by tying string between 1x2 wooden stakes set perpendicular to one another. Try to keep the string level and at least a foot off of the ground. Working off of this perimeter you should be able to determine and mark the center points of footing locations with paint or stakes. This works well for square decks but can get kind of dicey with irregular shapes like octagons.
Triangulation – Triangulation works particularly well with laying out complicated deck shapes accurately. You will need to work off of two fixed points along the house, the distance between which will form one side of your triangle. Using Decks.com footing layout plans and (2) 50’ cloth tape measurers you can measure the specific dimensions from each to these endpoints to the centers of each footing. You now know the three lengths of the sides of a triangle. If your tapes are held level; when you pull these tapes tightly together you will form a precise triangle directly above the center points of the footings.
Use a footing triangulation drawing to locate your footings based off of 2 known points along the house wall. Footing layout plans are available with all of our free deck plans. You can also hire decks.com to create custom deck plans that include a footing layout plan.
Use the dimensions on the footing plan to layout the footings in your yard. This process works best with 2 people with 50' cloth tape measures. Set the tapes at an even height at the points indicated along the house, pull the tapes to match the measurements for each dimension corresponding to the plan. The location where the tapes intersect will be the center of your footing.
Mark the center of the footing with spray paint. You can now verify the locations by measuring from center point to center point. If the footing locations are square you can prepare to dig. If the footing locations appear out of line you should double check that your tapes are level and that the stationary points match the footing layout drawing.