Deck vs. Interlock vs. Flagstone: What GTA Homeowners Should Know

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Every spring the same question lands in our inbox: deck, interlock, or flagstone? After 50 years building GTA backyards, here’s the framework I use when homeowners ask.

The climate reality

Toronto’s freeze-thaw cycle is brutal on outdoor surfaces. We get roughly 25-35 freeze-thaw events in a typical winter — water expands as it turns to ice, contracts as it melts. Whatever surface you choose has to move with that, or it cracks, heaves, and separates.

Interlock (concrete pavers) handles this well because individual pavers can shift slightly and be reset. A well-built interlock patio on a proper gravel base (6-8 inches compacted) with the right joint sand can outlast the house. A poorly built one — thin base, no geotextile, cut corners on compaction — heaves within two winters. This is why the contractor question matters as much as the material question. If you’re still in the early stages, this thread on what to ask before hiring covers the essentials.

Flagstone (natural limestone, bluestone, tumbled stone) is the most durable surface we install — but the least forgiving of a bad base. Natural stone doesn’t flex. If the base moves, the stone cracks or tilts. When it’s done right, it’s essentially permanent. Budget $35-70+/sq ft installed, more in tight-access yards.

Pressure-treated or composite decks work well and often make sense in raised-yard situations or where you need to step up to a back door. The big advantage is drainage — a deck sits above grade, so water moves naturally. PT wood needs staining every 2-3 years. Composite is lower maintenance but higher upfront.

The drainage question almost nobody asks until it’s too late

Before any of the three, I ask: where does your water go?

Spring 2026 is already showing why this matters. We’re seeing wet basements and ponding on flat lots across Scarborough, Etobicoke, and Mississauga right now. Adding impermeable surface — whether solid interlock or stone — without directing runoff away from the foundation is a recipe for wet basement calls by fall. We covered the grading-first principle in depth here.

Proper grading — 1/8" drop per foot away from the house — is non-negotiable before any hardscape project. In many cases that prep work costs as much as the patio itself. It’s not glamorous, but it’s the difference between a backyard you enjoy and one that causes foundation problems.

What are we actually spending in 2026?

Rough GTA ranges for supply and labour — not including demo, disposal, or drainage work:

  • Interlock (concrete pavers): $18-35/sq ft depending on pattern and access
  • Natural flagstone/limestone: $35-70+/sq ft
  • Pressure-treated deck (standard): $30-50/sq ft
  • Composite deck (Trex/Fiberon): $45-75+/sq ft

Disposal adds to all of these. Tipping fees in the GTA have risen to around $160-170/tonne, and a 500 sq ft project can generate 30+ tonnes of excavation and old material. Most quotes don’t make that line visible until you ask.

So which should you pick?

For most urban GTA lots under 1,500 sq ft of outdoor space: interlock is the most practical — durable when built right, versatile in design, mid-range cost. Flagstone for those who want a timeless look, have the budget, and can book an early-summer install slot. Deck if you’re dealing with raised grade, slope management challenges, or specifically want a wood-feel entertaining space.

What’s your backyard situation? Comparing these three for a spring project? Share below and I’ll tell you what I’d lean toward.

Your Spring GTA Home Checklist: 8 Things to Check Before Calling a Contractor
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Worth adding the maintenance angle since it factors heavily into the true cost of each option over a 10-year window.

Interlock: Low annual maintenance if the base was done right — re-sand joints every 3–5 years, re-seal if you want, reset any pavers that shift from freeze-thaw. The flexibility is the feature: you can lift and relay a section without matching grout lines or cutting stone. Cost to install in the GTA right now: roughly $18–$30 per square foot installed depending on the paver grade and complexity.

Flagstone: Almost zero ongoing maintenance — natural stone does not fade, chip, or stain easily. But if a slab cracks or tilts due to base movement, matching the original stone exactly three years later can be difficult (quarry batches vary). Cost: $25–$45 per square foot installed, more for premium limestone or irregular-cut designs.

Pressure-treated deck: The annual maintenance reality is often underestimated. Staining or sealing every 2–3 years, board replacement as they split and grey, hardware corrosion checks. A composite deck (PVC-core boards, aluminum framing) costs more upfront — roughly $45–$80 per square foot — but the 25-year maintenance profile is dramatically better than pressure-treated. If you are building a deck you plan to own for the decade, composite on aluminum framing is what I would put in for my own house.

The question I ask every homeowner: what do you actually want to do back there? Entertain and cook — deck often wins. Extend a natural garden feel or driveway approach — interlock or flagstone. A mix of both in separate zones is something we do fairly often on larger GTA lots.

The link in the original post to the hiring thread is the right next step if you are getting quotes — the base prep question alone will tell you a lot about who you are dealing with.