Every spring in Barrie and Orillia, we see the same thing: decks that were level in October are tilted, twisted, or pulling away from the house by April. The cause is almost always the same — footings that weren't deep enough.
What Frost Heave Actually Does
Simcoe County's frost line sits at roughly 4 feet (1.2 metres) below grade. When the ground freezes, water in the soil expands. That expansion pushes upward with enormous force — enough to lift concrete footings, deck posts, and anything attached to them.
If a footing sits above the frost line, the frozen soil grips the sides of the footing and lifts it. When spring comes, the soil thaws and settles — but the footing doesn't always settle back to exactly where it was. Year after year, the movement compounds.
The result:
- Deck boards that slope or feel springy
- Posts leaning at angles
- The ledger board pulling away from the house (this is a structural safety issue)
- Stairs that no longer meet the deck evenly
The Right Way: Below the Frost Line
Proper deck footings in this region go below 4 feet. That typically means one of:
- Poured concrete piers — sonotube forms dug to 4+ feet, filled with concrete, with a post bracket set in the top
- Helical piles (screw piles) — steel piles screwed into the ground below the frost line; faster to install, excellent in wet or clay soil, and removable
- Precast concrete piers on proper bases — only if the base itself sits below frost depth (most off-the-shelf deck blocks sitting on the surface do not qualify)
What doesn't work here, despite what big-box packaging suggests:
- Concrete deck blocks sitting on grade
- Short piers dug 2 feet down "because the soil felt hard"
- Posts buried directly in soil (they'll rot and heave)
The Ledger Board Connection
Where the deck attaches to the house, the ledger board must be properly flashed and bolted — not just nailed. A heaving deck puts tremendous stress on this connection. If the ledger pulls away, the deck can collapse.
Proper ledger installation means:
- Lag bolts or structural screws into solid rim joist (not just sheathing)
- Metal flashing above the ledger to direct water away from the house
- No ledger attachment to brick veneer alone — it needs structural backing
Permits and Inspections
Most municipalities in Simcoe County require a building permit for decks above a certain height or size. The footing inspection happens before you pour concrete — the inspector needs to see the depth of your holes.
Skipping the permit doesn't just risk a stop-work order. If an improperly built deck fails and someone is hurt, the liability falls on the homeowner.
What It Costs to Fix a Heaved Deck
Straightening a heaved deck is significantly more expensive than building it right the first time. It often means jacking the deck, excavating beside the existing footings, and installing proper piers — essentially rebuilding the foundation of the deck while the structure sits overhead.
Build it below the frost line from day one. It's the cheapest insurance a deck can have.
Concepts Construction — Barrie and Orillia, Ontario. Planning a deck? We'll build the foundation right so it stays level for decades. Free Estimates. Honest Solutions. (705) 330-2911.
