In order for your deck to last, the footings need to be solid. The best way to ensure your footings are solid is by creating them out of poured concrete. You'll need to check with your municipality to determine building codes for deck footings. In cold climates, you'll also need to dig the footings below the frost line. While not a difficult project, each detail is important, so don't rush the work. Allow about a day to finish.
Consult with your municipality's building code office to find out how deep the footings should be and how many you'll need to support your deck.
Mark out the dimensions of the deck, pounding stakes into the ground to mark the corners and running a string line around them.
Move the stakes and string lines aside. Dig holes to the appropriate depth using a post hole digger or gas-powered auger. Make the holes slightly wider than the concrete tube form. Flare the holes out about three inches at the bottom to form a wider base. This will help ensure a solid footing, especially in areas with harsh winters.
Add 2 inches of gravel to the bottom of the holes. This will help water drain away from the footings and extend their life.
Measure the depth of the holes and cut concrete tube forms with a saw to fit. The forms should extend two inches above the grade and extend two inches into the flared portion you created at the bottom of the hole. To suspend the tube in the hole, attach a temporary cross brace made of scrap lumber to the top of the tube with nails.
Place the tube forms into the holes, and ensure that they are level.
Mix the concrete according to the manufacturer's recommendations. It should have the consistency of wet oatmeal.
Pour the concrete into the form, tamping it with a stick all the way to the bottom to remove air bubbles or gaps. The concrete will fill the flared section then fill the tube.
Level the concrete using a piece of scrap lumber. Pull the scrap lumber across the top of the concrete. Check the top of the concrete and form to ensure that they have remained level.
Insert a 1/2-by-8-inch galvanized anchor bolt into the concrete at the center of each tube. It should sit so that 3/4 to 1 inch of it is above the concrete. Use a plumb bob to ensure that the anchor is positioned in the center of the tube.
Adjust the anchor bolt until a torpedo level reads plumb.
Allow the concrete to cure according to the manufacturer's directions. Then trim off the exposed part of the cardboard tube with a sharp utility knife. Backfilll soil around the footing, tamping it down firmly and mounding it slightly so that water will run off away from the deck.
Attach adjustable pole bases to the anchor bolt after the concrete has cured.