Subfloor preparation is the part of a flooring installation nobody photographs and everybody depends on. Whatever goes on top, whether hardwood, vinyl plank, laminate, or carpet, performs exactly as well as the surface underneath allows. Squeaks, hollow spots, cracked grout lines, gapping planks, and click joints that fail in a year almost always trace back to a subfloor problem that was visible, measurable, and fixable on installation day.
Late summer is when Tony’s Flooring sees the planning surge from GTA homeowners who want new floors finished before Thanksgiving hosting and the holiday season. That timing is actually favourable, because installing in early fall means the subfloor work happens before the furnace dries the house out for winter. This guide explains what proper preparation involves, why Toronto’s housing stock makes it especially important, and what a homeowner should expect to see a professional crew check before the first plank goes down.
Why Fall Timing Changes the Moisture Picture
Wood-framed houses breathe with the seasons. Through a humid Toronto summer, a plywood or plank subfloor absorbs moisture and expands; once the heating season starts, it dries and shrinks. Flooring installed over a subfloor at its summer moisture peak can open gaps by January as everything beneath it contracts. Installing in early fall, after the worst humidity has passed but before deep heating-season dryness, catches the subfloor closer to its annual average.
Good crews do not guess at this. A pin or pinless moisture meter reading of the subfloor, compared against the moisture content of the acclimated flooring, is the standard pre-installation check for wood products. Most hardwood manufacturers want the two readings within a few percentage points of each other before installation proceeds. Canada Mortgage and Housing Corporation publishes practical guidance on managing moisture and humidity in Canadian homes, and its central point applies directly to flooring: control moisture first, because every finish material downstream depends on it.
Flatness Is Not the Same as Level
A subfloor can slope gently toward one wall, as nearly every older Toronto house does, and still be a perfectly good base for flooring. What it cannot be is wavy. Flatness, meaning the absence of localized dips and crowns, is the specification that matters, and the common industry tolerance is roughly three millimetres of deviation over a three-metre straightedge. Click-lock floating floors are the least forgiving: a dip under a joint lets the floor flex with every footstep until the joint fatigues and fails.
Finding and Fixing the High and Low Spots
Crews map the floor with a long straightedge or laser, marking crowns and dips in pencil. High spots on wood get sanded down; on concrete they get ground. Low spots are filled with patching compound or, when a whole area rolls, with self-levelling underlayment poured across it. On a typical renovation this adds hours, not days, and it is the single highest-value step in the entire preparation sequence for floating floors like laminate and vinyl plank.
Securing the Structure: Squeaks End Here
Squeaks are subfloor panels rubbing against fasteners or joists, and the only time to silence them permanently is while the floor is bare. Preparation crews walk every square metre listening for movement, then drive screws through the subfloor into joists wherever panels have loosened from decades of nail withdrawal. Older Etobicoke and Scarborough houses with plank subfloors, boards laid diagonally across the joists, often get a layer of plywood screwed over the planks to create the continuous, stable surface that modern flooring warranties require. Loose boards, water-stained sections, and panels with delaminating plies get cut out and replaced rather than buried.
Concrete Slabs: Basements and Condos
Concrete brings its own checklist. New slabs need months to cure before flooring can go over them, and even decades-old basement slabs in Toronto transmit ground moisture upward year-round. A calcium-chloride test or a relative-humidity probe reading tells the crew whether the slab is dry enough for the chosen product, and the answer changes the design: many basements need a vapour retarder or an underlayment with a built-in moisture barrier between the slab and the flooring. Grinding handles paint overspray, adhesive residue from old tile, and crowned seams, while cracks get routed and filled so they cannot telegraph movement into the new floor.
Skipping the slab moisture test is the most expensive shortcut in flooring. Trapped moisture under a vinyl floor breeds adhesive failure and odour; under laminate it swells the core; under hardwood it cups the boards. Every one of those failures costs more to fix than the test costs to run.
Old Flooring, Underlayment, and Transitions
Whether existing flooring comes up or stays down depends on the new product. Floating floors can sometimes go over a single flat layer of old vinyl or tile, but stacking adds height, and height creates problems at doorways, appliances, and stair nosings. A dishwasher trapped under a new countertop by an extra centimetre of flooring is a renovation classic nobody enjoys. Crews measure finished-height consequences at every transition before deciding, and they trim door casings and jambs so the new floor slides under cleanly rather than being caulked against them.
Choosing the Right Underlayment
Underlayment is product-specific, not generic. Laminate wants a thin foam with the correct density; vinyl plank often wants none at all or only what the manufacturer approves, because soft layers under rigid vinyl let joints flex; hardwood nailed over plywood wants a paper or felt slip layer; and basements want vapour protection built in. Using the wrong underlayment is a warranty-voiding mistake that costs nothing to avoid at the planning stage. The product pages for hardwood flooring and vinyl plank outline what each system expects underneath.
What Preparation Adds to Budget and Schedule
On a house in good shape, preparation is a few hours of screwing off panels, skim-patching, and vacuuming, often folded invisibly into the installation quote. On a century semi with plank subfloors and a sagging hallway, it can be a full day of plywood overlay and levelling compound, and the quote should say so plainly rather than hiding it. Tony’s Flooring measures and inspects before quoting precisely so the preparation line is realistic, and the flooring cost calculator helps homeowners frame the overall budget before the in-home visit. For fall installations, booking the measure in August or early September keeps the project comfortably ahead of the holiday calendar.
Frequently Asked Questions
How flat does a subfloor need to be for new flooring?
The common standard is about three millimetres of variation over a three-metre straightedge, and floating click-lock products are the strictest about it. A gentle overall slope is usually acceptable; localized dips and crowns are what cause joint failure and must be ground, sanded, or filled first.
Can new flooring be installed over old flooring?
Sometimes. A single flat, well-adhered layer of old vinyl or tile can stay under some floating floors, but added height at doorways, stairs, and appliances often argues for removal. The existing floor’s condition and the new product’s requirements decide it case by case.
How long does subfloor preparation take?
For a sound subfloor, a few hours of fastening, patching, and cleaning on installation day. Houses needing plywood overlay, self-levelling compound, or slab grinding typically add one extra day, and concrete moisture testing is done during the initial measure so it never delays the installation itself.
Book Your Fall Installation Early
The difference between a floor that impresses for twenty years and one that squeaks by spring is almost always the preparation, and that work is exactly what an in-home measure is designed to scope. Tony’s Flooring inspects, quotes, and installs across Toronto and the GTA, with early-fall dates filling fast ahead of the holidays. Call (416) 255-9631 or book through the contact page to get your project on the schedule.