My deck company builds about 50 projects a year, running the gamut from basic to elaborate. That makes for a lot of footings, and I hate digging footing holes. The frostline in the area of New Jersey where I build is at 36 inches, and we're blessed with every rocky soil type known to man. Before I switched to helical piles, I wore out plenty of post-hole diggers and shovels, and I even bought a compact track loader with an auger to make installing deck foundations a little less offensive.
Digging the holes was only part of the fun. Next I'd have to schedule an inspection with building officials incapable of committing to a specific time or day, but with a knack for showing up after a heavy rain when my formerly pristine holes had become mud bogs. Sometimes, I'd get a red tag with a note saying, "Clean mud from bottom of hole." So after mucking out the hole (which I would have done anyway), I'd have to wait for a re-inspection.
Then I'd load 80-pound bags of concrete mix into my truck, unload them at the job site, and carry them to the back of the house. This would be followed by hours of joyless mixing in a wheelbarrow. If we used a ready-mix truck, it was a little easier, but they cost a lot for small jobs, could damage driveways, and didn't always show up on time. And we'd often still have to wheelbarrow yards of concrete from the street to the backyard.
Additionally, I always wondered how much weight my concrete piers could support. Without a soil engineering report, it's impossible to know the exact bearing capacity of the soil, so I'd usually over-build the footing to be safe.
Whenever I recognized bad soil conditions during excavation, I brought in a soil engineer, which was expensive and time consuming. The last time I did this, the homeowner ended up with a $6,000 change order for additional excavation, not including the soil engineer's fees.
About two years ago, I stumbled upon a photo of a deck project that wasn't built on concrete piers, and I emailed the contractor to inquire about what he had used. His answer - helical piles - changed my business.
I had never heard of helical piles and had to Google them to find out what they were. I learned that a helical pile is a manufactured steel foundation that screws into the soil (Figure 1). It has a lead or shaft - usually 7 feet long - welded to a helical bearing plate or helix, and a cap that attaches the shaft to the framing.
Figure 1. Helical piles are screw-shaped plates welded to a steel shaft. Various sizes are available for different soils and applications.
Typically, piles for residential use are hot-dipped galvanized steel (Figure 2). If the soil is particularly corrosive, sacrificial anodes (similar to those used to protect underground LPG tanks) can be used. In most commercial and industrial applications, however, the piles aren't even galvanized.
Figure 2. A thick coating of zinc protects the steel piles from corrosion.
The size of the helix will vary based on soil conditions. Generally, a helical pile installer will select a smaller helix for rocky soils and a larger one for marshy and clay soils. Once the pile is set, a variety of caps are available to tie the pier to the framing; some of them have a screw assembly that allows fine tuning of the elevation (Figure 3).
Figure 3. Several types of caps are available to attach piles to framing. Some can be adjusted in height to fine-tune a deck's elevation.
My first inclination was to dismiss helical piles as just another gimmick. But it turns out that they have been used for more than 100 years in the United States, mainly on heavy commercial projects. Structures far more engineered than a backyard deck, sunroom, or addition rely on helical piles for their foundations. I was so impressed that I bought a dealership and now install helical piles for other contractors, as well as for my own decks (see "Helical Piles for Residential Work").