Three Footings Used For Freestanding Signs

When it comes to freestanding sign structures, footings are critical, helping to transfer the load of the structure to the foundation while also increasing stability.

There are three main types of footings that are used. In this blog, you will learn some of the major benefits of each footing, an overview of their complexities, and when best to use them.

Round Footings

• Also known as augered or caisson footing.

• Best for large structures such as taller freeway or highway signs 70 to 150-feet-tall, but can fit all size needs.

• Large structures can be supported by columns with diameters of  2 feet to 8 feet or more.

• Small structures can be supported by columns with diameters of 4 inches to 12 inches.

• Least amount of concrete required and surface space used.

• For large structures, a round footing involves the highest amount of labor, requiring equipment such as caisson drills, which are costly, and a heavy rebar cage and corrugated sleeve to prevent the hole from collapsing; allows for virtually unlimited diameter and depth capabilities.  Requires stable soil conditions and low water table.

• For smaller structures with a footing diameter of 36 inches or less, round footings are  quicker and less expensive to install and do not typically require rebar.

• Relies on lateral soil pressure mainly, but vertical bearing pressure needs to be checked.

Block (Square) & Vertical (Rectangular) Footings

• Also known as square and rectangular  footings.

• Best for mid-size sign structures 20 to 50-feet high or less.

• Column diameter depends on overall width and height of a sign, but can be as small as 4 inches up to 2-feet.

• Require the least amount of labor because of the way they are dug—excavated with a track excavator or backhoe.

• Vertical footings are ideal for tight areas, especially in commercial applications when working within curbs in parking lots.  

• Rectangular footings are the easiest to dig because you don’t need to reposition the excavator or backhoe (as you would with a square footing.)

• Tends to be more expensive as more concrete is needed.

• Relies on lateral soil bearing instead of vertical bearing (Spread footings rely on vertical bearing pressure.)

• Rebar not required if you go direct burial in most circumstances. For anchor bolt/base plate designs, rebar cage (vertical around perimeter, with horizontal ties).

Spread Footing

• Spread footings rely solely on vertical soil bearing pressure and require greater surface area.  

• If turned sideways, the spread footing becomes a vertical footing, as described above.

• Best for larger signs—30-feet high or taller. (Once loads start increasing, the square/rectangular footing type design becomes less efficient and more concrete would be required than a spread footing.)

• Column diameter are determined similarly like block and vertical footings—by overall width and height of a sign, 1 foot to 3 feet in diameter.

• Good for poor soil conditions and high water table, but requires rebar mats on the top and bottom; soil stabilization may also be required by adding gravel or replacing several feet of soil and compacting every foot on the size.

• Spread footings are shallow, but its bottom must still to go below frost line. Where poor soil conditions are present, engineer may require structural pilings to be driven into stable ground depending on the size of structure and vertical loads to be exerted directly into soil area below footing.

• There is an alternate spread type that includes a concrete pier on top of a spread footing. This is often spec’d by building engineers. The pier on top of the spread is used to get the bottom of the spread down to the frost level instead of making the entire spread the total height to grade (36 inches or more.) The spread is placed down low and is 12 to 18 inches thick, then a square pier is formed to the top of the spread footing and tied together through rebar coming out of the footing.   The pier is then brought up to grade to save concrete where anchor bolts are typically set to accept the sign.

Getting Grip on Stable Footings

As you can see, selecting the right footing for your sign structure is no simple undertaking. We’ve painted a picture for you using broad strokes—just to give you an idea of what to consider. However, choosing the right footing greatly depends on soil conditions, space available, the size of the structure, and budget. To truly understand what to look for, we recommend speaking to a  sign company like DCI Signs & Awnings who works directly with a structural engineer with experience in this type of work.