Every deck we build in the GTA starts with the same argument — helical piles or concrete sonotubes. It's the first real money decision on the quote, it's the one most homeowners don't know they're making, and it's the one that determines whether your deck is still flat in ten years or sitting half an inch low on the southeast corner.
We've built decks on both. We've also torn out enough failed sonotubes in Oakville, Burlington, and Mississauga clay to have a strong opinion, and we'll walk you through ours with real numbers, real Ontario Building Code references, and zero hand-waving.
Before we get into it — there's nothing wrong with concrete footings in principle. They've held up decks in this country for eighty years. But principle and Ontario clay are two different things, and the failure mode we see most often is a homeowner who paid for footings once and is now paying for them again because the first crew didn't respect what the ground does between November and April.
How deep should deck footings be in Ontario?
Deck footings in Ontario must extend below the frost line, which the Ontario Building Code (OBC 9.12.2.2) sets at a minimum of 1.2 metres — roughly four feet — for most of southern Ontario including the entire GTA. That number isn't a suggestion. It's the depth at which the ground stops freezing in a typical winter, and anything that bears load above that line will move when the soil below it freezes and expands.
In practice, we go deeper than code. Our standard concrete footings get dug to 4 feet 6 inches, because the top few inches of that hole are almost always disturbed fill and we want the bell sitting on undisturbed native soil. Our standard helical pile spec is driven to 6 feet — sometimes 8 on sandy or disturbed lots — not because code requires it but because the pile won't stop until it hits the torque reading we need, and the torque reading we need happens to live below the frost line in this part of the province.
The homeowner joke is always the same: "wait, four feet, really?" Yes, really. Frost heave doesn't care how expensive your deck is — it will lift a 12,000-pound structure an inch overnight if the footing is at three feet instead of four. We've seen it. We've torn one out.
- OBC 9.12.2.2 — minimum footing depth of 1.2 m (≈4 ft) below finished grade in southern Ontario
- Oakville, Burlington, Mississauga, and most of the GTA sit on silty clay with a documented frost line at 4 ft
- Our concrete spec: 4 ft 6 in dig, bell-bottomed sonotube, tamped gravel base
- Our helical spec: 6 ft driven minimum, confirmed by torque reading at the powerhead
- Snow load in Oakville is 1.63 kPa (roughly 34 psf) per OBC Table 1.1.3.1 — we design to 60 psf to be safe
What's the difference between helical piles and concrete sonotubes?
A concrete sonotube is a cardboard tube dropped into a hand-dug or augered hole, filled with ready-mix concrete, and topped with a post bracket. A helical pile is a steel shaft with one or more helix-shaped plates at the bottom, driven into the ground hydraulically by a powerhead until it hits a calibrated torque reading. Both are trying to do the same job — transfer load through weak topsoil down to stable bearing soil — and both can work. They just work differently, and they fail differently.
Concrete footings cure in place, which means you need to dig, pour, and then wait before you can start framing. In April, when the ground is still half-frozen in the mornings and a downpour can fill your hole in twenty minutes, that waiting is where most of the trouble starts.
Helical piles install in a day, get load-tested as they go in, and you can stand on them an hour later. On a six-footing deck in Mississauga last October we had the piles down by 10 a.m. and joists flying by 2 p.m. Try that with concrete.
The honest tradeoff is price. Helical piles from a local installer — usually Postech or Techno Metal Post in our area — run about $400 to $600 more per footing than a poured concrete equivalent. On a twelve-pile deck that's $4,800 to $7,200 in extra footing cost. That's real money. It's also real money compared to a second tear-out if a sonotube cracks, which runs about $900 per footing to rip out and replace after the deck is built on top of it. For the full line-item price of the decks we build on these footings, see what a custom deck actually costs in the GTA in 2026.
- Concrete sonotubes: roughly $250–$400 per footing installed, 24–72 hour cure before framing, manual depth verification
- Helical piles: roughly $650–$1,000 per footing installed, same-day load capacity, torque-verified depth
- Postech and Techno Metal Post are the two installers we use — both offer a written load rating per pile
- Standard residential pile carries 20–30 kN (roughly 4,500–6,700 lbs) at the head
- Failed sonotube replacement: $800–$1,200 per footing to tear out and replace after the fact
When does a concrete footing still make sense?
Concrete sonotubes still make sense when the soil is clean sandy loam or gravel, the deck is small and low to the ground, the budget is genuinely tight, and the crew doing the work treats the pour like it matters. On a 10×12 pressure-treated platform in someone's side yard, with a fresh lawn, no drainage issues, and a homeowner who watched us hand-dig the holes — concrete is fine. It's been fine for decades. There's no reason to spend an extra $3,000 on piles if the ground is cooperative.
Where we stop recommending concrete is anything raised, anything over 12 feet off the house, anything on clay, and anything where we can't verify the bottom of the hole is on native soil. The raised decks are the ones that kill us — the taller the deck, the longer the lever arm, and a footing that moves a quarter inch at the bottom moves three inches at the railing. That's the moment a homeowner stops trusting the deck. And once they stop trusting it, we're back out there with a Sawzall.
One more honest note on concrete — the bag-mix, mix-it-on-site approach most DIYers and some handymen use is where 80% of our tear-outs come from. Ready-mix delivered from a truck is a different material than 40 bags of Quikrete mixed in a wheelbarrow. If someone quotes you concrete footings and the word "truck" isn't in the quote, ask what they're actually pouring.
What we found tearing out failed sonotubes in Oakville
Last spring we were called out to a wraparound deck in Oakville where the handrail moved when you leaned on it. The original crew had poured ten sonotubes six years earlier, the deck had passed inspection at the time, and the homeowner assumed the movement was cosmetic. It wasn't.
When we pulled the first deck board, we found that three of the ten footings had cracked in a horizontal plane about 18 inches below the top, two had heaved a full inch with frost, and one had separated entirely from the post base and was sitting in a puddle of groundwater.
The diagnosis was boring. The original footings had been dug to about 36 inches — a foot shy of frost depth — and the backfill around them was loose topsoil instead of compacted gravel. Water collected at the base, froze, expanded, cracked the concrete, then repeated the process forty times a winter for six winters.
We replaced all ten with six helical piles (the new frame only needed six with proper spans) driven to 6 feet, rated together for a 90 psf snow load even though Oakville only requires 60. Two years later the deck doesn't move, the handrail is where we left it, and we haven't been back. If you're picking between surface materials for that same frame, our cedar vs composite vs pressure-treated breakdown walks the tradeoff.
That job is the case we tell every new client, because it compresses the whole argument into one visit. Ten bad footings, one bad winter, a full tear-out, and a price tag that would have been a third of the cost if the original crew had just gone a foot deeper with the auger. The dry joke we make to the homeowner is that frost heave is the only contractor in Ontario who always shows up on time.
“The first deck looked finished. This one feels finished.”
- Three of ten sonotubes had horizontal cracks — classic freeze-fracture signature
- Two had heaved a full inch, lifting the joists off the post bases
- One had separated entirely from the post cap and was sitting in standing groundwater
- Original dig depth was 36 inches — a full foot short of the 4-ft OBC minimum
- Replacement: six helical piles at 6 ft, driven in a single morning, framing back up by the end of day two
