Footings are the one part of a deck you cannot see and cannot easily fix later — so get them right the first time. Below we answer the eleven footing questions homeowners ask most, for Ontario’s freeze-thaw climate. This page is part of our complete guide to building a deck in Ontario.

How deep, and where do footings go?

Use the planner for your region’s frost depth and the footing type that fits, then read the sizing and rules below.

How deep do footings have to be for Ontario frost? Is 3 feet enough?

No, 3 feet is not enough. The minimum is the greater of 1.2 m (4 ft) or your local frost depth. That’s about 1.2 m through most of southern Ontario, and deeper — commonly built to 1.5 m — in the Ottawa and colder zones. Footings above the frost line heave.

What’s the frost depth in my region?

It varies across the province. As a rough guide: GTA and southern Ontario about 1.2 m; Ottawa and eastern Ontario commonly 1.5 m; Simcoe County (Barrie, Oro-Medonte, Springwater) about 1.2–1.5 m; Muskoka and the north deeper still. Always confirm the figure with your local building department.

My footings heaved over winter — why, and how do I fix it?

Heave means the footing didn’t reach below the frost line, or it bore on disturbed or organic soil that holds water. Frost grabs the sides and lifts it a little more each year. The fix is to replace it with a proper frost-depth footing or switch to helical (screw) piles.

Can I pour in cold weather, and does it have to bear on undisturbed soil?

Footings must bear on firm, undisturbed (native) soil at the base of the hole — never on loose backfill or organic topsoil. Avoid pouring onto frozen ground; if you must pour in cold weather, use cold-weather concrete practices and protect it from freezing while it cures.

Deck blocks, sonotubes, or piles?

Can I use deck blocks instead of poured footings — is it legal?

Only for a low, freestanding, roofless deck: generally where the deck is not attached to the house, the underside of the joists is under 600 mm above grade, and the deck is under about 55 m². Anything attached, taller, or roofed needs frost-depth footings.

Sonotube vs Bigfoot vs helical/screw piles — which?

A sonotube on a flared base is the standard DIY choice. A Bigfoot is just a pre-formed flared base for the bottom of the tube. Helical (screw) piles skip the digging and curing but must be designed and signed off by a Professional Engineer, which adds cost.

Do I need footings for a ground-level floating deck?

A genuinely low, freestanding deck (joists under 600 mm above grade, not attached, no roof) can usually sit on deck blocks on a compacted, drained base. As soon as it’s taller, attached, or roofed, you’re back to frost-depth footings — check the permit triggers in our deck permit guide.

Sizing and connecting your footings

What diameter does the footing or sonotube need to be?

The minimum sonotube is usually 10–12 inches, but diameter alone isn’t the whole story — the base must be sized to the load each post carries (its tributary area). Heavier loads need a wider flared base, even if the tube stays 10–12″.

Do I need a bell or flared base, and how big?

Usually yes. A flared base spreads the load onto the soil, sized to the tributary area — for example, roughly a 10″ base for a lightly loaded post up to a 24–36″ base for a heavily loaded one. Don’t flare more than about 4″ wider than the tube unless you use a formed base.

How many footings and posts does my deck need?

It comes from your beam and joist spans, not guesswork. The beam size and number of plies sets how far apart the posts (and footings) can be, and the joist span sets the beam line. Our framing guide has the span tables that decide the count.

Post-on-saddle vs post embedded in concrete?

Use a galvanized saddle (post base) that holds the wood post just above the concrete. Embedding a wood post in concrete is the detail to avoid — it traps water at grade and rots the post from the bottom, often within a few years.