By Jon Eakes

What is a deck foundation supposed to do? It should support the load without sinking and that requires footings. It should resist frost upheave both by having the footings below the frost line and in clay soils that are susceptible to adfreezing, minimizing ice lens adhesion. And, a somewhat new factor in Canadian weather, it needs to resist wind uplift from extreme weather-meaning it needs to be anchored down.

The most commonly sold deck support does none of these things. The popular DIY deck blocks, fondly called elephant feet, rely on exceptional soil conditions to not sink with a load-or rise with frost-and they have no hold down capacity against wind uplift, although the wind effect can be countered by cabling the deck beams down to screw auger type of ground anchors. They don't meet any building codes and technically should only be used for free-standing structures that fall outside the building code, like a garden gazebo, but my son built his deck with them anyway. Whatever happened to the TV show Father Knows Best?
The tradition in proper construction where excavation equipment was present was to excavate large holes and build a wooden form below the frost depth to pour footings to receive concrete columns.

Enter the Big Foot
Big foot, developed in Nova Scotia, is a tapered cone, sized on the top to perfectly fit various diameter SonoTubes. A hole is excavated, but no forms built. The SonoTube is screwed to the foot and lowered into the hole, allowing for the pour of any height column. Then the concrete is poured from the top, forming the footing and the column at the same time. Often another cone is placed upside down temporarily on the top to act as a funnel for the concrete pour. Because the footing formwork is closed, the excavation can be partially backfilled prior to the concrete pour to stabilize the position and fill an open excavation.
The SonoTube company has followed this idea and now markets a similar plastic device in a rectangular form more traditional to column footings.
     

The Footing Tube
The Footing Tube evolved in New Brunswick as a specific response to adfreezing problems with uniform cardboard concrete forms. This invention forms both the spread foot and the vertical column up to grade level into a single waterproof tapered plastic form. With the pyramid shape right up to grade level, both a slip surface and a decreasing diameter mean total freedom from adfreezing lift.
This is an excellent product for serious clay frost prone soils. There are no cardboard forms to get damaged by over-exposure to water. The footprint can be increased by simply snapping on an expander to the bottom of the tube. Depth marks allow for inspection even after backfilling. As with the BigFoot, it can be backfilled immediately, even prior to pouring concrete, to avoid safety problems with open excavation holes. The closed top keeps the void clean and dry and avoids anything falling or crawling in prior to pouring concrete, only cutting it open at the moment of the pour. Bracket hardware is sunk into the concrete a few inches above grade level so this will not make tall concrete columns. In staying with the maritime competitive spirit, Big Foot has recently developed a slightly tapered 4-foot plastic tube that attaches to their Big Foot base to create the possibility of an all plastic frost-proof installation very similar to that of the Footing Tube.

The Evolution of Helix Spirals
We have used helix spirals welded to a shaft to dig holes for a very long time now, with the endless screw efficiently lifting dirt out of deep holes. Then someone thought of only leaving one rotation of helix at the bottom of the shaft- and they invented ground anchors used to anchor cables into the ground. Much later someone figured out that, with proper sizing, the helix at the bottom of the shaft could be used as a footing driven below the frost line without any excavation at all-and Spiral Footings were invented.

The Ground Hog
The Ground Hog spiral deck footing was appropriately developed in the Manitoba prairies. It is a hollow square shaft that is quite popular for deck footings. It is designed to be manually installed by two people using a long turning bar. The stabilizer fins are dropped into place after the screw is driven to its proper depth. Just above ground level an adjustable plate can accept many types of hardware brackets for the wooden structure above.
           

PosTech Screw Piles
PosTech is a relatively new company out of Quebec that is spreading across Canada. It uses a larger round tubular shaft but operates much the same as the GroundHog. The helix is wider and flatter than most as it is specifically engineered for installation with small but powerful specialized one man driving rigs. It is rather impressive to watch the driving operation start on the layout mark painted on the soil-then shove to the left, then to the right, to realign the drive around rocks and through hard clay. They end up placed with impressive accuracy. Although screw piles have been around for a long time, specialized franchised equipment is making backyard deck building with screw piles a clean and quick alternative with no more access than a walking path. Of course bedrock stops them dead.
The latest innovation from PosTech is an insulated foundation screw. The hollow structural tube has the upper portion filled with foam insulation to minimize frost following the pipe into the ground.  

SonoTubes
You all know SonoTubes, which is actually a brand name for one mark of round cardboard tubes designed to form vertical concrete pillars or columns. After the concrete cures, the tube is stripped off of the column down to grade level as it does not weather well, even where it cannot be seen.

Fast-Tube Fabric Formed Concrete
Fast-Tube is a product that evolved out of Fab-Form fabric formed concrete developed in B.C., which was initially a linear footing form for foundation walls. If you haven't already seen that product, it is worth taking a look at: a high-density polyethylene hydroscopic fabric that forms strip footings and stays in place to protect them from rising damp. Then they developed squares of the fabric to create Fab-Form column footings-quick footings with only a few stakes to hold the fabric-no forming plywood.
It was only logical to evolve that fabric into a tube and place it vertically. Tack it into place on a single 2x support and simply fill it from the top to give you a perfect column. All your column forms from 8" to 20" diameters in a roll-just cut to length. Stripping is quick and easy, revealing a nice smoothly finished concrete column.

Smooth Finish Free columns
Most poured concrete columns have that cardboard-formed spiral winding its way up the column. Under a deck that has no great importance, but since there are times when a more finished look is desired, SonoTube didn't want Fast-Tube to have the only polished columns.
Finish-Free forms from SonoTube are smooth inside, leaving no spiral or other marks on the column. The StripCord allows for zipper-like removal of the cardboard forms to keep that smooth finish unscratched and intact.

Montreal-based TV broadcaster, author, home renovation and tool expert Jon Eakes provides a tool feature in each edition of Home BUILDER.
www.JonEakes.com