Concrete footings are required for supporting the heavy loads placed by walls. These footings vary depending on the needs of the construction project. These footings range from single support structures to monolithic footings that are combined with concrete floor slabs in one pour. Understanding footing types can help you make better decisions on your own construction project.
The single concrete footing may extend for several hundred feet, forming a square or straight line. This type of footing is usually 12 inches deep and 16 to 24 inches wide and smooth on top. This type of footing will support large amounts of structural weight, depending on the width and depth of the footing. Typically, this footer is poured into a excavated trench that is the same width and depth as the footing. The trench serves as the footing form.
Keyed footings are poured similarly to single footings. These footings are poured into prefabbed wooden forms that are built on top of the soil. A four-inch wide notch is placed in the top of this footer by placing a 2-inch by 4-inch board along the top length of the footer while the concrete is still wet. The lumber is pressed into the concrete and removed after the footings have dried. Later, when the concrete walls are poured onto the footings, the wall concrete will run into this groove in the footer, forming a keyed interlock between the wall and footer.
Monolithic footings are distinct from other types of footings because they form one single structure between the footings and the concrete slab. These footing trenches be excavated in conjunction with the slab floor. The footings are excavated 12 inches deeper than the floor excavation and extend along the outside of the structure walls similar to a single footing. However, when the concrete is poured for the footings and floor, they are poured at the same time, creating an integrated, or monolithic, floor system.
Footings that are not required to support large amounts of weight are called shallow footings. These footings are poured no deeper than eight inches and no wider than 16 inches. Typically, these footings are designed to support porches and small garden walls. Nonetheless, they are poured and installed in the same way as a single footer.
- "Foundations and Concrete Work";Fine Homebuilding;2003
- "Masonry & Concrete"; Benjamin W. Allen; 1997
- "Formwork for Concrete Structures"; Robert Leroy Peurifoy, Garold D. Oberlender; 1996
- Photo Credit Jupiterimages/Photos.com/Getty Images
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