I was told many years ago, a footing that is uniform and 6 inches deep is better than one that is approximately 12 inches but varies a couple of inches from place to place. This is true because of weight distribution and settlement. Keep in mind that the concrete in that hole may not be seen, but it is the foundation for everything on top. If you mess up on floor covering and need to have it replaced, no sweat. Try pulling the footing out from under the building!

Unless you are using a pick and shovel to do the footings, it may be best to have a professional do the work. Take it from someone who has dug footings by hand, the cost is worth it to rent equipment or pay someone else.

Width and depth of footings are controlled by varying climates and soil conditions. Your footing should be below the frost line. Here in the south, that is about eight inches and requirements usually call for the shallowest to be twelve inches below finished grade. Another factor is the soil material and compaction. It is great to have your footing sitting on virgin clay, but that may not be possible. We won’t go into those requirements for this down and dirty (catch the pun) calculation. If you are working from approved plans, the requirements should be there.

A rather standard footing is 24” wide x 8” deep. If we are building a 40’ square building, the math is 160 x 2 x .67 = 214.40 cu. Ft. Now, divide by 27 (the number of cubic feet in one yard), and we get approximately 8 cubic yards of concrete. Keep in mind, there is a large waste factor with concrete (especially if you do not have uniform ditches). Many people calculate 20 percent more for that, but that is high if you keep your ditches uniform. If you were ordering material for this job, and of course, if the footings were dug uniformly, 9 yards of concrete would probably be what to order. This is more in line with a 10 to 12% waste factor. Never skimp on concrete by ordering less and hoping it will be enough. When the plant has to send another truck out with a half yard, they generally charge you extra.

Steel required in footings will vary for the same reasons as depth and width. You should estimate it based on getting 18’ from a 20’ bar times the number of bars required. Each rod has to be lapped by the next bar and tied with wire, thus you don’t get 20’ of running footage from a bar. Rod chairs, those little wire things that hold the bars of the ground, are figured about every four feet of footing. It is very important to keep the steel in the concrete.

Grade stakes should be driven into the center of the footings about 6 to 8 feet apart. Shoot the top of the grade stakes to make sure they are all the same level. You can buy short pieces of rebar for your stakes, don’t use wood. If you are going to have a block foundation, the top of your grade stakes should be in multiples of 8 inches below the top of your foundation.

Because it is easier to build up mortar under a block than it is to take off part of the block, most contractors will hold their grade stakes down 1/4 to 1/2 inch.

Although footings are not a finished product, it is important to keep them smooth and level for the person working behind. Laying brick and block on rough concrete that is high in some areas and low in others presents obvious problems for the mason.

Talk to you later.

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