A floating deck is the cheapest way to get a real deck in an Ontario backyard, and it is also the deck we are most often asked to fix. The ones that fail are almost always built the same way: blocks set straight on soil, a deck bolted to the house, or a hot tub dropped on top. None of that is a problem with deck blocks. It is a problem with using them where the Code never meant them to go. This guide covers the rule, the build and the cost, as we do it across Hamilton, Burlington and Oakville.
The rule that allows deck blocks
Normally a deck footing in this region has to go below the frost line, which in Hamilton-area clay means at least 1.2 m deep. Ontario Building Code Article 9.12.2.2, Sentence (7), switches that requirement off for a deck that meets every one of these conditions:
| Condition | Limit | What it means in practice |
|---|---|---|
| Height | Not more than 1 storey | A single-level deck, not a raised second-floor deck. |
| Area | 55 m2 or less | About 590 sqft. A 20 x 28 ft deck is just under. |
| Clearance | 600 mm or less from finished ground to the underside of the joists | About 24 inches. Measured to the bottom of the joists, not the top of the boards. |
| Roof | Does not support a roof | No roofed pergola or gazebo carried on the deck frame. |
| Attachment | Not attached to another structure, unless differential movement will not adversely affect that structure | Freestanding, with a gap at the house. No ledger board. |
Fail any one and the deck needs footings below frost, or helical piles. Separately, most municipalities do not require a building permit for a deck that is not attached to the house and is no more than 600 mm above grade, but check yours: Halton Hills, for example, requires a building permit for any platform over 10 m2 around a pool under its pool enclosure by-law. Our Hamilton, Burlington and Oakville permits guide covers the local rules.
Deck blocks compared with the alternatives
| Foundation | Installed cost | Use it for | Frost behaviour |
|---|---|---|---|
| Deck blocks on compacted gravel | $30 - $60 per block | Freestanding low decks that meet all five conditions | Moves slightly with frost and settles back |
| Adjustable pedestals on an existing slab or patio | Varies by system | Decking over a sound concrete pad or patio | Moves with the slab |
| Helical piles | $350 - $650 each | Attached, raised or roofed decks, especially in clay; no digging | Below frost, stays put |
| Concrete footings below frost (sonotube) | $250 - $650 each | Any deck, the traditional standard | Below frost, stays put |
A typical 300 sqft deck needs 8 to 12 footings, so the foundation alone is usually $2,500 to $7,500 of a conventional deck quote. That is what a floating deck saves. For the full price picture, see our deck cost guide.
How to build a floating deck that stays level
- Book locates. Call Ontario One Call before you dig. Gas and cable lines often run right where a deck goes.
- Strip the sod and topsoil across the whole footprint, down to firm subsoil, usually 4 to 6 inches.
- Lay landscape fabric and add 4 to 6 inches of 3/4 inch crusher run (Granular A), compacted with a plate compactor in thin lifts. This pad is what makes a floating deck work. Blocks set straight on soil sink unevenly, especially in clay.
- Grade the pad so water drains away from the house and out from under the deck. Standing water under a deck is what lifts it in winter.
- Set the blocks on the compacted pad, level them to each other with a string line or laser, and keep the spacing tight enough for the beam you are using. Do not stack blocks or shim with wood.
- Use ground-contact lumber. Posts, beams and joists this close to the ground stay damp. Use pressure-treated lumber rated for ground contact, and put joist tape on the tops of the joists.
- Keep it off the house. Leave a gap of an inch or two at the wall. Do not bolt a ledger on, and keep the deck surface below any door threshold so frost lift cannot jam the door.
- Let it breathe. A low deck has very little airflow. Do not close the sides in solid. Our deck skirting guide covers skirting that vents properly.
- Check it each spring. A floating deck can shift a little through a hard winter. Re-level any block that has dropped while the deck is still light enough to lift.
What not to put on deck blocks
- A hot tub. A filled hot tub with people in it weighs several tonnes. Set it on its own pad at grade and build the deck around it, or design a framed deck on footings for the load.
- A roof. A roofed pergola or gazebo breaks the Code condition and catches wind and snow load the blocks were never meant to carry. A freestanding pergola on its own footings beside the deck is fine.
- Anything attached to the house. Including stairs that tie the deck to a door landing.
- A deck on a slope. Once the high side needs posts tall enough to put the joists more than 600 mm off the ground on the low side, you are out of the exemption.
What a floating deck costs
| Option | 2026 Ontario range |
|---|---|
| Floating deck, pressure-treated, installed | $25 - $45 per sqft |
| Conventional deck on footings, pressure-treated | $30 - $55 per sqft |
| Conventional deck, cedar | $45 - $75 per sqft |
| Conventional deck, composite | $60 - $110 per sqft |
| Deck blocks | $30 - $60 per block installed |
A floating deck saves the footing line and usually the permit, but not the boards, which are the bulk of the cost on a composite deck. Our deck cost calculator gives a figure for your size and material, and pressure-treated vs cedar vs composite covers the material choice.
Floating deck or patio?
At ground level a floating deck and a patio do a similar job. A deck is warmer underfoot, quicker to build and easier on a yard that slopes gently. A paver patio lasts longer, needs no staining and handles a fire table or a hot tub without fuss. If you are choosing between them, see deck vs patio.
Frequently asked questions
Are deck blocks allowed in Ontario?
Yes, for a deck that is one storey, 55 m2 or less, no more than 600 mm from the ground to the underside of the joists, not supporting a roof and not attached to another structure. That is Ontario Building Code Article 9.12.2.2, Sentence (7).
Do I need a permit for a floating deck?
In most Ontario municipalities, no, if it is freestanding and no more than 600 mm above grade. Some towns add their own rules, for example Halton Hills requires a permit for a platform over 10 m2 around a pool, so check locally.
How far apart should deck blocks be?
That depends on the size of the beams and joists. Keep them close enough that the beam spans within its rating, and set every block on the same compacted gravel pad so they settle evenly.
Will a floating deck heave in winter?
It will move slightly with frost and settle back in spring. A compacted gravel pad, good drainage and a gap at the house keep the movement small and harmless. Check and re-level in spring if needed.
Can I attach a floating deck to my house?
Not if it sits on deck blocks. An attached deck must have footings below frost unless it is designed so movement will not affect the house, which in practice means footings or helical piles.
Can I put a hot tub on a deck on blocks?
No. A filled hot tub weighs several tonnes. Put it on its own pad at grade and build the deck around it, or build a deck on footings designed for the load.
How much does a floating deck cost?
About $25 to $45 per square foot installed in pressure-treated wood in 2026 Ontario, saving the $2,500 to $7,500 footing line a conventional 300 sqft deck would need.