Pier footings can be used as footings for a myriad of structures ranging from decks, shed, coops, porches as well as many others. Pier footings are round in shape and generally are three to four feet in length (depth) depending upon the frost depth in your area.
Sizing the diameter of the piers can be done by using a form three times the size of the post bearing upon it. Six inch posts require an eighteen inch diameter pier form. Many areas today require an architect or engineer to size these footings depending upon local soil conditions. Check with your local building department for permit requirements before starting the work.
There are commonly known names for these paper forms such as S—tubes but there are many other generics that work just as well. One local contractor uses the cardboard rolls inside new carpeting that he gets from the local carpet store dumpster for free. Since the forms are intended for a one time use only, brand names are not important.
Once you have determined the footing depth you need, cut the tubes into lengths that size. A word of caution, keep the tubes dry at all times until you use them. Do not stack them one on top of the other as the weight of the upper tubes will crush and deform the ones on the bottom of the pile.
The tubes are made of paper and will absorb water making them sag and become useless. Once all the holes for your footings are dug and are hopefully dry, place the forms into the holes and we recommend keeping the top of the form a minimum of two inches above the surrounding grade. This prevents earth from getting to the post and decaying them.
Back fill each tube carefully without using large rocks that can puncture the sides of the tubes. Keep checking during back filling that the top of the tube stays at the elevation you want it to be. Once back filled the tubes cannot be moved.
Place earth around the tube in a way that will shed any rain water away from the tube and cover the tube with a piece of plywood or heavy plastic to prevent rain water from entering the tube itself as well.
Double check that the centers of all the tunes are in their correct locations and then figure how much concrete you will need. Using the formula “pi x radius (squared) by the length of the tube” and then by dividing that number by twenty seven and multiplying that number by the total number of piers, you will then have the number of yards of concrete you will need to fill all the forms.
Pi in case you need the number is pi (π)=3.14 which is close enough for figuring concrete. Always round up the amount ordered to account for spillage but don’t over order. 3.7 yards should be a four yard order. Another word to the wise. Most concrete companies charge an extra fee for a “short load” delivery which is less than 6 yards.
You pay the same for 4-5 or 6 yards no matter what you order. Ask ahead of time and if that is the case, pre-form a stair landing pad, a curb or maybe some sidewalk that could be poured at the same time as the piers. You get the best bang for the buck as they say.
Keep the forms dry until you are ready to pour. Ground water can cause the forms to sag and implode making them useless. No inspector will pass crushed forms and if you are inclined to pour them anyway, when frost pushes the uneven sides of your footing up out of the ground destroying the building above, you will clearly see why the smooth sides of the tubes is necessary.
Frost has a much harder time gripping a smooth sided round pier than an odd shaped piece with many edges and angles to grip. When placing the concrete use a pole or piece of reinforcing rod to plunge into the wet concrete as it is placed to assure there are no air pockets present in the finished product.
Let the concrete dry and using a sharp utility knife carefully score and remove that portion of the finished tube that will be exposed to view above ground.
You may then proceed with building your structure.