How to Dig Deck Footings
Looking for detailed instructions on how to build a footing (or footer) for a deck? Use these instructions for any project requiring digging postholes.
Footers built properly will provide a stable foundation to support the deck and absorb not only the weight of the deck but the load on the deck. If you put up posts without footings the posts will sink to the ground and take the deck along with it. Local laws are established because parts of the country will have different frost lines or none at all. The footings need to be built lower than the frost line, otherwise the footings could move when the soil is frozen.
Digging footings can be moderately challenging.
Digging large holes in the ground can be hard work and you can injure yourself. Don't be ashamed to ask for help or get a contractor to do some or all of the work. Digging the holes and pouring concrete can be labor intensive unless you have help from other people, the right equipment, or both.
As an example, you may need the following:
Power Auger (optional - there are several types)
Concrete tube post
Lot's of muscle
Make a plan and determine the size of the footings required to build your deck. See Fig 1 for a diagram of a typical footer or footing. Concrete footings are required to support structures attached to homes. In all cases you will need to dig past the frost line, which will vary by location. For example, 24 inches, 30 inches, or 42 inches. Some states have a frost line of 60 inches in certain areas.
The deck design will determine the diameter of the footings. The local engineers (the people that will approve your deck) will provide recommendations. Example diameters are 10, 16, 18, 24, and 32 inches.
Note: The frost line is the maximum depth where the ground will freeze in the winter. Footings below the frost line will prevent movement. Even a movement of 1 inch could damage a structure.
Get the proper approvals to do the deck work. Coordinate with the utility company to verify that there are no utility lines in the area where you are digging holes. Normally, this service is free and you may not need to be at home when they do the work.
Mark the location of holes. Marking chalk works very well. If you have stringers, make sure you are able to relocate the center of the holes. Because after you dig, the hole may not be perfect. It could be oval, off centered, or some funny shape. See Fig 2.
There are two ways to dig: Hand or Machinery. The best way to dig by hand is with a post digger as shown. See Fig 3.
There are several types of machinery you can use: one man powered auger, two man powered auger, and an auger you can tow. The auger can be a dangerous machine even if with a two man auger. You have to be a very strong person to operate the augers comfortably.
Use extensions for the augers to dig deeper holes.
Here is an example of a one man powered auger. See Fig 4.
Here is an example of a two man powered auger. See Fig 5.
Here is an example of a power auger you can tow. See Fig 6.
If you choose to use a post digger, be patient. It is very tedious and can appear to have no end in sight. You could hurt your back and your hands. So take breaks or have someone help.
If you come into a large stone, concrete, or other junk that is solid and in the way, use a heavy post hole digging bar to break the stone or concrete into smaller pieces and remove by hand. A large crowbar can also be used. If the bar is not strong enough, use an electric or gas powered jackhammer or pneumatic drill.
Ensure that the depth is just a little bit past the target depth. If it is 30 then make it 31 or 32. Loose dirt in and around the hole could make its way at the bottom again. If you plan to put concrete tubes, ensure that the width is slightly bigger than the tube so that it will fit.
Now you are ready to pour concrete and other materials for the deck post.