A subfloor is the structural layer that sits between your joists and your finished flooring — it's what everything else rests on. In Ontario, where basements are the norm rather than the exception, and where the GTA's clay soil and high water table create real moisture challenges, getting the subfloor right is not optional. It's the difference between a floor that lasts thirty years and one that buckles, squeaks, or cups within five.
Top Floorings Depot works with every subfloor type across the GTA — from century-old plank in East York semis to fresh pour in new-construction Markham condos. This guide covers what Ontario homeowners and contractors need to know about each subfloor type, how to prepare them, and which Top Floorings products work over each.
What Is a Subfloor and Why Does It Matter in Ontario Homes?
Your subfloor is the load-bearing surface that bridges your floor joists and carries everything — your finished floor, your furniture, your family. In the GTA, most homes built before 1990 use tongue-and-groove plank subfloors (typically ¾" to 1" solid wood). Homes built from the 1990s onward typically use OSB (oriented strand board) or plywood sheathing. Condos and newer semi-detached builds often have a concrete slab as the primary subfloor, especially in below-grade areas.
The Ontario Building Code (OBC) sets the minimum structural requirements for floor sheathing in residential construction. For joists spaced 16 inches on centre — the most common spacing in GTA homes — the Code requires a minimum of 5/8" tongue-and-groove OSB or ½" plywood when a finished floor will be applied directly. For 24-inch on-centre joist spacing, that minimum rises to ¾" sheathing. These are the floors that GTA contractors deal with daily, and they are the baseline for every finished floor we install.
Plywood Subfloors: The Standard for Toronto-Area Homes
Plywood is the traditional subfloor material in the GTA, and for good reason — it has proven performance over decades of Ontario winters and humid summers. The standard is CDX-grade plywood (C-facing, D-back, exposure durability) for floor sheathing, though in better-finished homes or where tile is being installed, many contractors step up to ¾" tongue-and-groove (T&G) plywood for superior interlock between panels.
Plywood handles the GTA's humidity fluctuations better than OSB in some respects — it expands and contracts more uniformly and is less prone to edge swelling if exposed to prolonged moisture during construction. This is a real consideration during GTA new builds where walls and roofing aren't yet closed in and subfloors sit exposed through a Toronto spring.
For finished flooring, the thickness of your plywood subfloor determines what you can install over it. Thick ¾" plywood allows for direct nail-down of solid hardwood. Thinner 5/8" or ½" plywood requires engineered hardwood (which can be glued or floated) or a secondary layer of underlayment before solid flooring. At Top Floorings Depot, we stock 7½" wide European Oak engineered hardwood starting at $3.69/sqft — the product most GTA contractors specify for direct installation over plywood in upstairs rooms and condos.
OSB Subfloors: Budget-Friendly and Code-Compliant
OSB (oriented strand board) overtook plywood as the dominant floor sheathing in Canadian residential construction in the early 2000s, primarily due to cost. In the GTA, the majority of homes built since the mid-1990s have OSB subfloors — and for most finished flooring types, this is not a problem.
The Ontario Building Code treats 7/16" OSB as equivalent to ½" plywood for single-layer floor sheathing over 16-inch OC joist spacing. For 24-inch OC spacing or for tile installations, the required thickness increases to ¾" OSB or a double-layer system (7/16" OSB plus ½" plywood or a cement board layer under tile).
One important note on OSB in Ontario: OSB is more susceptible to moisture absorption than plywood. If your OSB subfloor was exposed to rain during construction or shows any swelling at the panel edges, that needs to be addressed before any finished flooring goes down. Light sanding to remove surface swelling and allowing the panels to fully dry to interior moisture levels (below 12% MC) is the standard remediation before proceeding.
Top Floorings Depot carries both plywood and OSB-ready German-made laminate flooring from $0.50/sqft for installation over OSB sheathing — the click-lock Valinge or Unifit systems on most modern laminate float cleanly over a properly prepared OSB surface with an appropriate underlayment.
Concrete Subfloors: The Foundation for Basements and Condos
Concrete subfloors are the rule in GTA basements, on-grade additions, and in most Toronto condo buildings. For homeowners and contractors working on the hundreds of thousands of basements across Scarborough, North York, Mississauga, and beyond, concrete subfloor prep is a daily reality.
The critical rule for concrete subfloors in Ontario: the concrete must be fully cured before finished flooring is installed. The OBC and most flooring manufacturer guidelines specify a minimum 28-day cure for poured concrete before flooring installation. Beyond that, moisture testing is mandatory. The ASTM F1869 calcium chloride test requires that concrete emit less than 3 lbs of moisture per 1,000 sq ft over 24 hours before impermeable finished floors (including SPC vinyl and engineered hardwood) are installed over it.
For basements with elevated moisture readings, a moisture mitigation system — a cement-based resurfacing compound or epoxy moisture barrier applied before the finished floor — is required. This is one of the most commonly skipped steps in GTA basement renovations, and it's the primary cause of flooring failures in below-grade installations.
The good news for GTA homeowners: concrete subfloors actually simplify a lot of decisions. You cannot nail down solid hardwood (it requires a wood subfloor), but you can install SPC vinyl plank flooring directly over a clean, flat, dry concrete surface with no underlayment needed (most SPC products have attached pad). For a warmer surface or when radiant heating is involved, engineered hardwood with a 3mm or 4mm wear layer is the standard recommendation — it handles the thermal movement of concrete better than solid wood and looks indistinguishable once installed.
Moisture Barriers and Subfloor Preparation in GTA Climate
Ontario's climate is one of the most demanding in Canada for flooring. Hot, humid summers (Toronto averages 70% RH in July) followed by dry, heated winters (20-30% RH inside) create seasonal expansion and contraction cycles that test every flooring joint and seam. Add to that the GTA's high water table and clay-based soils, and moisture management becomes the central concern in most subfloor prep situations.
For concrete subfloors in GTA basements especially, a separate moisture barrier beneath the finished floor is standard practice. Most SPC vinyl products have this built in (the IXPE or EVA pad attached to the plank back serves as the moisture barrier). For other flooring types, a 6-mil polyethylene vapour barrier over concrete, taped at seams, is the minimum requirement before underlayment is installed.
For wood subfloors, the primary concern is interior humidity control. An OSB or plywood subfloor in a typical Toronto semi with a finished basement below and living space above needs to reach interior equilibrium moisture content (typically 6-8% MC in GTA heated homes) before finished flooring is installed. We recommend a 72-hour acclimation period with HVAC running to normalize conditions, especially in new construction or post-renovation situations where the structure hasn't yet reached balance.
Top Floorings Depot offers professional vinyl and SPC installation and laminate flooring installation across the GTA. Our installation teams handle subfloor assessment as part of the preparation process — moisture testing, flatness measurement, and surface prep are included in the scope before any finished floor is installed.
Common Subfloor Problems in Ontario Homes (and How to Fix Them)
The most frequent subfloor issues Top Floorings Depot sees in GTA homes:
Squeaking: Caused by nails or screws that have loosened from joist movement over time. Fix by screwing (not nailing) into the joist at the squeak point. Never use construction adhesive alone — it locks the panels in place but doesn't draw them down tight against the joist.
Bounce or deflection: Suggests undersized joists or spans that are too long for the joist spacing. Fix options range from sistering new joists alongside existing ones, to adding a mid-span beam or column, to simply specifying a stiffer finished floor product (SPC vinyl is more rigid than laminate or hardwood and reduces perceived bounce).
Swollen or delaminated OSB edges: Usually from exposure during construction or a leak. The fix is cutting back the damaged area and filling with a cement-based patch or replacing the affected panels. Do not install finished flooring over swollen or softened OSB — the core has been compromised.
Concrete out of level: Poured concrete that is more than 3/16" out of level over 10 feet needs levelling. For small depressions, a Portland cement-based patch works. For larger areas, a full-depth self-levelling compound is the standard fix. Never use shims or thin underlayment to bridge a low spot — it will compress over time and the finished floor will telegraph the depression.
How to Choose the Right Subfloor for Your Project
The short answer: if you have a wood subfloor (plywood or OSB), you have more flexibility in finished flooring choice — you can go with solid hardwood, engineered hardwood, laminate, or SPC vinyl. If you have a concrete subfloor — especially below grade — your options are engineered hardwood, laminate, or SPC vinyl.
For contractors working on GTA multi-unit or semi-detached projects: OSB subfloors are now the standard in most production builds. Budget accordingly for moisture testing and any remediation on OSB panels that may have been exposed during the build. The cost of a moisture mitigation step before flooring installation is a fraction of the cost of a full flooring failure and re-install.
For homeowners in older GTA homes with plank subfloors: the plank may be thinner than modern sheathing, and a ½" ply underlayment layer may be needed before your finished floor goes down. This is especially true for tile installations — ¾" solid hardwood or tile requires a very specific subfloor assembly that typically includes two layers totalling at least 1⅛" thickness.
Our Top Picks for Concrete Subfloor Installations
If you're installing over a concrete subfloor — especially in a basement or condo — here are two products from Top Floorings Depot that are purpose-built for that application:
Swiss Krono 14mm Witches Wood AC6 — 14mm total thickness with a 6mm core, Valinge 2G locking system, and AC6 (commercial-grade) durability rating from $0.50/sqft. The German manufacturing standards and the heavy core weight mean this laminate stays flat and rigid over concrete, with minimal telegraphing of subfloor irregularities. The Witches Wood colour (deep grey-brown grain) works well in modern and transitional basement suites. Box coverage is 16.15 sqft.
Riche Washed Driftwood 10mm SPC — 10mm total thickness (8mm core + 2mm EVA attached pad), 20mil wear layer, and Valinge 5G Drop Lock. The 10mm thickness provides excellent sound dampening in multi-unit condo buildings (the IIC rating on 10mm Riche with EVA pad is among the highest in its class), and the waterproof rigid core handles basement moisture conditions without hesitation. 23.64 sqft per box, available in wide 7.09" plank for a more premium look in basement rec rooms and condo living areas.
Visit Top Floorings Depot
Top Floorings Depot
3781 Victoria Park Avenue, Unit 1
Toronto, ON M1W 3K5
www.topfloorings.com
Call: 416-499-0117 | Text: 416-770-8819
Showroom Hours: Monday–Friday 9–5:30 | Saturday 9–4 | Sunday Closed
We serve homeowners and contractors across Toronto, Scarborough, North York, Mississauga, Brampton, Markham, Richmond Hill, and Vaughan. Whether you're working with a concrete basement subfloor, a plywood second-floor assembly, or a brand-new OSB sheathing in a Markham semi, our team can advise on the right finished floor for your subfloor conditions. Visit our showroom at 3781 Victoria Park Ave to see products in person and speak with our flooring specialists — no appointment needed.
Have you worked on a GTA renovation with challenging subfloor conditions? Tag us on Instagram @topflooringsdepotgta or leave us a review on Google — we love hearing about GTA projects.