Published
Most people shopping for a new floor spend their time on colour, plank width and whether to go with laminate or vinyl. Almost nobody asks what's underneath. That makes sense, because you can't see it. But on a floating floor, what's underneath decides how long the part you can see keeps looking right.
Here's what goes wrong when a floating floor goes down on a subfloor that isn't flat, how flatness is checked, and how to read a quote that includes levelling, or one that doesn't.
What a floating floor is
Most laminate and luxury vinyl plank installed in homes today is a floating floor. The planks click together along their edges and lie on an underlay, which is sometimes attached to the back of each plank. They aren't glued or nailed to anything below. The whole floor rests on the subfloor as one connected sheet.
That makes it quick to install. It also makes it sensitive to what's beneath it. Wherever the subfloor goes, the planks either follow it and bend at the joints, or bridge over it and leave an air gap underneath.
Flat is not the same as level
A level floor is horizontal: a marble wouldn't roll across it. A flat floor has no humps or dips: a long straight edge lies on it without rocking or leaving gaps.
Floating floors care about flat. A floor in an older house can slope slightly from one wall to the other and still take a new floor well, as long as the slope is even. A floor that is close to level but full of dips and ridges is the one that causes trouble. When installers talk about levelling, they usually mean flattening: taking down the highs and filling the lows.
One exception: a slope that is new, or getting worse, can point to a problem in the structure underneath. That is worth having looked at before any new floor goes down.
What happens when the subfloor isn't flat
These problems rarely show on installation day. They appear weeks or months later, once the floor has been walked on, furniture has settled and the house has been through a change of season.
- Seams that open up: every step over a dip flexes the planks at their joints. Over time the click-lock edges wear or crack, and gaps appear along the boards, often in a line across the room where the low spot is.
- Hollow spots: where a plank bridges a low area there's air underneath. You hear it as a hollow, drummy sound and feel it as a slight give underfoot.
- Bounce: a floor that moves when you walk on it is straining every joint in that area, and it rarely settles down on its own.
- Clicking and creaking: planks rubbing at a stressed joint make noise. It's often mistaken for a squeaky subfloor, and it doesn't go away on its own.
- Peaked edges: over a hump, the ends of two boards can be pushed up into a ridge you can see in low light and feel through socks.
None of these can be properly fixed from the top. Repairing a low spot usually means taking the floor up back to that area, fixing the subfloor and relaying it, often with some new boards, because click edges don't always survive being taken apart.
The warranty problem
Laminate and vinyl plank come with a manufacturer's warranty, and the installation instructions say how flat the subfloor has to be. Many ask for something in the range of 3/16 of an inch over 10 feet (about 5 mm over 3 metres), or 1/8 of an inch over 6 feet (about 3 mm over 1.8 metres). The exact figure varies by product and is printed in its instructions.
If a floor fails and the subfloor turns out to be outside that tolerance, the manufacturer can refuse the warranty claim, because product warranties generally exclude problems caused by the subfloor or the installation. The planks didn't fail; the preparation did. A homeowner who saved on levelling can end up paying for a new floor out of pocket, on a product that was supposed to be covered.
How flatness is checked
Nobody can tell whether a subfloor is flat from photos or from the doorway. It has to be measured, and the tool is simple: a long straightedge or level, usually 6 to 10 feet long (roughly 2 to 3 metres).
- The straightedge goes down in several directions: along the room, across it and on the diagonals.
- Anywhere it rocks, there's a high spot under it.
- Anywhere there's a gap beneath it, there's a low spot. The gap is measured against the manufacturer's tolerance.
- Highs and lows are marked on the floor so the levelling goes exactly where it's needed.
You can do a rough version yourself on a bare floor. Lay the longest level you have, or a board you know is straight, and shine a flashlight along the floor from behind it. Light showing underneath tells you where the dips are. A warped board will mislead you, which is why a level is the better tool.
One caveat: if carpet, old tile or another floor is down now, the full picture only shows once it's removed. A careful installer checks what they can at the measure and tells you plainly what might change after removal.
If the house was built before 1990, old sheet vinyl, older floor tiles and the adhesive under them can contain asbestos. In BC, a qualified person has to check materials like these before workers disturb them, so ask about it before any old floor comes up.
What levelling actually involves
Levelling isn't one product poured over the whole house. It's targeted work, and the method depends on the subfloor.
- On concrete, such as a basement slab, high spots are ground down and low spots are filled with a floor patch or self-levelling compound.
- On a wood subfloor, loose or squeaky sheathing is screwed down to the joists, raised edges where two sheets meet are planed down and dips are filled.
- Either way, the floor is checked again with the straightedge before the underlay goes down.
There's a limit worth knowing. A floor that bounces because the joists underneath are undersized, damaged or sagging needs a structural repair first. Levelling flattens the surface; it doesn't stiffen the frame.
Levelling also adds time. Patch and self-levelling compound have to dry before anything goes over them, anywhere from a few hours to a day or more depending on the product and how thick it is. That's one reason levelling belongs on its own line of a quote rather than being folded quietly into installation.
Why the quote with levelling is often the honest one
Collect a few quotes for the same room and you may find one includes levelling and another doesn't. It's natural to assume the cheaper one is the better deal, and sometimes it is. Some floors are genuinely flat and need nothing.
But a quote with no levelling can also mean the floor was never checked. Then the cost appears partway through the job as an extra, or the floor goes down uneven and the problems show up later.
A quote that names levelling, and says where it's needed and why, is telling you what the installer actually found. That's the one you can plan around. Questions worth asking any installer before you sign:
- Did you check the subfloor with a straightedge, and what did you find?
- Is levelling included, and for which areas?
- What happens if the old floor comes up and the subfloor is worse than expected?
- What flatness does the manufacturer of this floor require?
The honest answer is sometimes "your floor doesn't need it." Levelling a flat floor is money spent for nothing, and you shouldn't be sold it by default. Not every floor needs levelling. Every floor does need checking.
Check first, then choose the floor
A floating floor is only as good as what it sits on. Gapped seams, hollow spots and bounce often trace back to a subfloor that wasn't flat, and they're expensive to fix once the floor is down. Checking takes minutes, and levelling where it's needed costs less than relaying a floor.
WoodPro Flooring does floor levelling as well as laminate and vinyl installation in Maple Ridge, Pitt Meadows and across the Lower Mainland. To book a free on-site measure, call (604) 787-5557 and mention the subfloor when you book. There's no obligation, and calls are usually returned the same day.