How to pour a concrete footing
It's hard to think about spring, but, believe me, it's just around the corner. You may have ambitious plans to build that long-awaited DIY room addition this year. Good for you. Many a homeowner just like you has successfully completed a small, simple room addition.
All structures need a great foundation so they can stand the test of time. Foundation walls almost always are supported by a footing. The footing is the lowest structural item that's found in most houses. Its purpose is to spread out the weight of the structure onto the soil. A footing is just a concrete beam that's poured in direct contact with the soil. The foundation wall rests on this footing.
You can access a handy quick-start guide for concrete footings with more tips and a full tool list here: go.askthebuilder.com/footer.
Check with your local building department concerning building permits and the frost depth in your area. The bottom of the footing needs to be below the frost depth. It's always a great idea to go just a little deeper than recommended.
Be sure you locate and identify any underground utilities before you dig. Call 811, and have all utilities marked so you don't get hurt or cause neighbors to have problems if you slice into a buried electric, water or gas line.
You can dig by hand, but tool rental businesses now rent very small excavators that can fit in a small yard. You don't need a full-size backhoe to dig a shallow footing.
Footings need long pieces of reinforcing steel. One-half-inch diameter, No. 4, is almost always sufficient. Because the steel needs to be continuous in the footing, don't butt two pieces together. Instead, overlap two pieces of the steel rods by at least 16 inches.
The shape of the footings is rectangular. You should make them at least 8 by 20 inches -- 8 by 24 inches is probably better. The 8-inch dimension is the thickness and the larger measurement is width.
You can just pour the cement in a 24-inch-wide trench if you like. It's key that the concrete be level. Drive vertical pieces of reinforcing steel into the soil every 4 feet in the center of the footing as leveling reference points. Use a laser level or builder's transit to get the tops of these pins at the same height.
Have plenty of help on hand when the cement truck arrives. Be sure to have spare wheelbarrows in case one breaks. Don't overfill them, as cement is very heavy. Consider renting a small machine with a bucket that you can use to make trips from the cement truck to the footing.
Wear rubber boots if you're working in the trench to level the cement. Cement will cause burns to skin, so wash off any as soon as possible. Use a simple wood float or magnesium float to smooth the concrete.
Summary: No part of this task, other than digging the hole and toting the cement, is really hard to do. It's all a matter of common sense and thinking the job through. Be sure you double check that the footing is square before you dig. Lay out the foundation on the ground before digging. When the diagonal measurements are the same in a square or rectangular foundation, it's square.
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