Pressure-treated lumber is still the cheapest, most-built deck material in southern Ontario in 2026. Roughly two-thirds of new residential decks in the GTA suburbs and easily 80% of decks in Brampton, Hamilton, Oshawa, and Ajax go up in PT. Composite gets most of the marketing oxygen, but PT is what most homeowners actually build.
Below is what a PT deck costs installed across Ontario in 2026, in CAD before HST, with the line items that move the price and the trade-offs people forget to budget for.
The 2026 baseline number
For a basic pressure-treated deck on a level lot in the GTA in 2026, expect installed pricing of $30–$45 per square foot. That’s the all-in rate the calculatoruses for PT — lower than composite by 40–50% per square foot, higher than the old “$25/sq ft” rule of thumb you’ll still see quoted on Reddit because lumber and labour both climbed roughly 20% between 2022 and 2026.
For the four most common deck sizes in southern Ontario:
- 10 × 10 (100 sq ft): $6,000–$9,500 installed (low-elevation PT, aluminum railing, 3 steps to grade, permit included). The minimum-project floor pulls the per-sq-ft rate above $50/sq ft at this size — fixed costs dominate.
- 12 × 12 (144 sq ft): $7,500–$11,500 installed.
- 12 × 16 (192 sq ft): $9,500–$14,500 installed. The most common GTA suburban backyard size.
- 16 × 20 (320 sq ft): $14,500–$22,000 installed.
Those numbers come straight out of the calculator. Cities where PT is the local default — Brampton, Hamilton, Oshawa, Ajax — show the same numbers on their per-city size tables. Toronto, Mississauga, and the rest default to composite because that’s what dominates new GTA-central builds.
What you’re actually paying for
On a PT deck, the material itself is a smaller share of the installed line than people assume — roughly 20–30%. Labour is 40–50%. The rest is railings, stairs, fasteners, permit, and the contractor’s margin. The three biggest movers within that:
- Lumber grade.Most GTA contractors quote MicroPro Sienna or Wolmanized #2 grade as their default. #1 grade adds roughly 12–18% to material cost (fewer knots, straighter boards, easier install). On a 200 sq ft deck that’s $400–$700.
- Joist depth and spacing.A 2×8 joist frame at 16″ centres is the cheapest legal frame. Going to 2×10 at 12″ centres for a stiffer feel (no bounce when you walk on it) adds roughly $4–$7 per sq ft — $800–$1,400 on a 200 sq ft deck. Worth it on higher-elevation decks; usually unnecessary at ground level.
- Fastener choice.Hot-dip galvanized screws are the price floor. Stainless steel adds $0.50–$1.50 per sq ft. Hidden-fastener systems aren’t common on PT (the boards aren’t dimensionally stable enough for most clip systems) — if your contractor proposes them, ask why.
Where the spread comes from
1. Regional pricing variance
PT pricing in Ontario varies by region more than composite does, because lumber yards in different parts of the GTA carry different supply chains. Roughly:
- Halton (Oakville, Burlington, Milton):Upper half of the range — premium markets and longer driving time from yard to site push pricing up.
- Toronto core and central Mississauga:Upper half — small lots, restricted access, parking permits, and material-staging fees all add overhead.
- York, Peel suburbs, Durham:Middle of the range — the default GTA pricing band.
- Hamilton, Brantford, Niagara:Lower half of the range — lower contractor overhead, shorter material transit, more local competition.
2. Elevation
A 30″ ground-level PT deck and a 6-ft-elevated PT deck use very different framing plans. Above 24″ you need a guard rail. Above ~5 ft most municipalities want engineered footings, which adds $400–$1,200 in survey and engineering. Above 8 ft you’re into stamped-drawing territory and the cost difference versus a ground-level deck can be 40–60% installed.
3. Demolition
Replacing an existing PT deck with a new PT deck is one of the most common projects in the GTA. Demolition runs $4–$8 per sq ft of the old deck — $800–$1,600 on a typical 200 sq ft replacement. Disposal is usually included; some contractors itemize the dump-fee separately.
The trade-offs people forget to price in
The reason PT looks dramatically cheaper than composite at install is that the install number is the start of the cost, not the end. Three things to budget for honestly:
Annual sealing
A PT deck in southern Ontario needs sealing every 1–2 years to prevent surface checking and grey-out. DIY: $150–$280 per year (cleaner, sealer, two days of effort). Contracted: $500–$900 per year on a typical 200 sq ft deck. Over 15 years — the realistic lifespan of a well-maintained PT deck — that’s $2,250–$13,500. The wide range is the difference between DIY and full contracting.
Board replacement
Even with sealing, individual PT boards crack, cup, or split within 8–12 years. Expect to replace roughly 5–15% of surface boards by year 12. On a 200 sq ft deck that’s $200–$600 in lumber plus a half-day of labour if contracted ($300–$500).
Eventual rebuild
A PT deck installed in 2026 will need either a major refit (new surface boards on existing frame) or a full rebuild somewhere between year 15 and year 25, depending on maintenance and exposure. Refit is roughly 40–50% of new-build cost; full rebuild is essentially new-build cost in inflated 2040s dollars.
Even with those costs honestly tallied, PT is usually still cheaper than composite over a 25-year horizon for owners who actually do the sealing themselves. For owners who won’t, the math gets close enough that composite becomes the better purchase. The detailed comparison is in our cedar vs composite breakdown — the PT-vs-composite math runs in the same direction with the install gap a little wider.
When PT is the right pick
Pressure-treated remains the right call for:
- Budget builds. If $14K is the budget for a 200 sq ft deck, PT lets you build it at the right size and composite forces you to either shrink it or carry the build into next year.
- Owners who genuinely will do the maintenance. The honest test: did you maintain the fence?
- Short-term properties. Selling within 5 years: a new PT deck adds nearly as much to listing price as a new composite deck, for half the cost.
- Secondary or low-use decks.Side decks, basement walkouts, decks off bedrooms — the maintenance burden is real but limited because the surface gets less weather exposure.
Run your specific dimensions through the calculatorand toggle between PT, cedar, and composite — the per-line breakdown is the clearest way to see the trade-off in your own units.