A floor that sat flat in May can feel snug and slightly raised by late July, with no spill or leak anywhere in sight. The usual cause is the air itself. Solid hardwood, engineered hardwood and laminate all pick up moisture from humid indoor air, and each plank grows a little across its width. Most summer humidity hardwood floors questions come down to one reading, the relative humidity (RH) in the room, and to whether the air conditioner runs long enough to pull it down. This page covers above-grade rooms through a GTA summer: published target ranges, the first signs of trouble, a simple routine, and real boards from our engineered hardwood collection and our solid and laminate ranges.
Quick answer: what humid summer air does to wood and laminate
- Keep the room in range. The National Wood Flooring Association (NWFA) gives 30% to 50% indoor RH as its general rule for solid wood flooring, and says to follow the manufacturer's requirements for factory-finished boards.
- Laminate has its own installation window. Swiss Krono's click-laminate instructions from its German operation call for 50% to 60% relative humidity during installation and the first three days after.
- Air conditioning is on your side. The NWFA notes that air conditioning removes moisture through condensation, and advises against shutting the HVAC system down for prolonged periods.
- Watch for early signs. Tight boards, slightly raised edges and puffy-looking laminate joints are your cue to check the hygrometer.
Why indoor humidity rises in summer, even with the windows shut
The NWFA's installation guidelines describe summer as the season when moisture vapour pushes from outside the house toward the inside. They also make a point many homeowners miss: cooling air lowers its ability to hold moisture, so indoor RH naturally rises as the temperature drops. What saves the floor is that an air conditioner pulls water out of the air as condensation while it cools.
Moisture leaves the house only while the system is actually cooling. On a mild, damp week when the AC barely switches on, or when it is turned off while the family is away, nothing is removing moisture, and the floor slowly takes it up.
Air conditioner habits that help the floor
- Leave the system on during holidays. Raise the setpoint if you want to save energy, but keep it running rather than switching it off for a week.
- Close windows on humid days. Letting sticky outdoor air in while the AC is trying to dry the house works against both.
- Add a dehumidifier when needed. The NWFA suggests a dehumidifier in the summer and humid months to help keep wood from gaining moisture.
Winter is the mirror image: heating dries the air and boards shrink. That season is covered in our guide to winter humidity and hardwood gapping in Toronto.
Published humidity targets for each type of floor
These ranges come from the NWFA and from the makers of two products we carry.
| Floor | Published RH range or limit | Where it comes from |
|---|---|---|
| Solid wood flooring, general rule | 30% to 50% | NWFA Wood Flooring Installation Guidelines (with geographic exceptions) |
| Factory-finished solid or engineered | The manufacturer's stated range | NWFA Wood Flooring Installation Guidelines |
| Appalachian solid hardwood | 35% to 55%, before, during and after installation | Appalachian Flooring solid flooring installation guide |
| Swiss Krono click laminate (German instructions) | 50% to 60% while installing and for three days afterwards | Swiss Krono Germany click laminate installation instructions |
For a house with both of the hardwood rows above, the overlap of the NWFA and Appalachian ranges is 35% to 50%. Holding the house inside that band keeps both within their published figures and gives you one target for a dehumidifier. The Swiss Krono figure is an installation window rather than a year-round range, so for laminate or any other product, read its installation sheet or ask us for it.
How solid, engineered and laminate floors respond to humid air
Solid hardwood
A solid board is one piece of wood from top to bottom, so all of it can take on moisture. Width matters here. The NWFA states that narrow boards expand and contract less than wider boards of the same species and cut. Our two solid examples are both 4 1/4" wide: Appalachian Natural Red Oak in Excel grade, and Lauzon Essential Hard Maple Sapphir, a 3/4" thick Canadian-made board.
Appalachian's own guide asks for 35% to 55% RH, so 55% is the ceiling a humid July tests for the red oak.
Engineered hardwood
Engineered flooring puts a real wood wear layer over a layered core. In the words of the NWFA, engineered wood flooring is, in general, more dimensionally stable than solid wood flooring, which matters most for wide planks. Our Villa European Oak is 7.5" wide and 3/4" thick, with a 3mm oak wear layer and a nail-down installation method. The top layer is still wood, so the room still needs to stay inside the manufacturer's range.
Laminate
Laminate's core is made from wood fibre. Swiss Krono's US FAQ explains that laminate flooring in general has a high-density fibreboard core that shrinks or swells depending on temperature and surrounding humidity. The same FAQ notes that conditions can differ from room to room, which is why it calls for a T-moulding in doorways so each room's floor can move on its own. Swiss Krono Grey Oak (MV 803) is a 10mm, AC5 click-lock laminate made in Germany, and at $2.49 per sq ft it costs less than half as much as any of the three wood floors here.
Here is how the four boards compare:
| Product | Type | Specs used here | Box price and coverage | Price per sq ft |
|---|---|---|---|---|
| Swiss Krono Grey Oak (MV 803) | Laminate | 10mm, AC5, click-lock | $42.83 per 17.22 sq ft | $2.49 |
| Villa European Oak | Engineered hardwood | 7.5" wide, 3/4" thick, 3mm wear layer | $97.00 per 19.42 sq ft | $4.99 |
| Appalachian Natural Red Oak | Solid hardwood | 4 1/4" wide, Excel grade | $101.87 per 18.9 sq ft | $5.39 |
| Lauzon Essential Hard Maple Sapphir | Solid hardwood | 4 1/4" wide, 3/4" thick | $99.80 per 17 sq ft | $5.87 |
Prices checked October 6, 2026. Price per sq ft is the box price divided by the box coverage.
Early signs a floor is absorbing summer moisture
- Boards feel tight. Hairline gaps you saw in February close up, and planks press firmly against each other and against thresholds.
- Edges sit a touch high. Run a hand across the grain. If the long edges of many boards are higher than their centres, read our explainer on why hardwood cups in GTA homes first.
- Laminate joints look raised. A slight ridge along joints in a room with no spill points to humid air. Our page on laminate lifting at the seams covers the fixes once a joint has come up.
If water was actually spilled or leaked, treat it as a water problem rather than a humidity one.
A summer routine for main-floor and upstairs rooms
- Put a hygrometer on each floor of the house. Check it morning and late afternoon during the first hot week, and jot the readings down so you can see whether a room drifts high only on certain days.
- Let the AC run. Keep it on through humid stretches and avoid long shutdowns.
- Bring in a dehumidifier if RH stays high. Set it to the top of your floor's range, or to 50% if you are using the shared band above.
- Check doors and windows. The NWFA recommends carefully monitoring exterior doors and windows for leaks during the summer and humid seasons.
- Keep the perimeter clear. The NWFA's maintenance list includes removing debris from expansion voids within the flooring system, so make sure nothing is wedged into the space at the walls.
When tight boards need more than a dehumidifier
- RH is above range and the floor is tight but flat: bring the room down into range and give the boards time to settle. This is ordinary seasonal movement.
- RH is above range and laminate joints are raised: correct the air first, then follow the seam guide linked above if the ridges remain once readings settle.
- Wood edges stay higher than the centres after RH is back in range: room air may not be the whole story. Our article comparing cupping and crowning in Toronto homes explains how to tell the two shapes apart.
- Damage is still visible after the season ends: the question becomes repair or new boards, and our guide to the cost to refinish hardwood versus replacing it walks through both routes.
Picking a floor for a room that runs humid in July
For a room that runs damp in summer, match the product to the humidity control you are willing to do:
- You want a wide oak plank: engineered hardwood fits, given the NWFA's note on dimensional stability. Villa European Oak at $4.99 per sq ft is the example above.
- You want traditional solid wood: choose a narrower board and commit to a hygrometer. Both of our solid examples are 4 1/4" wide.
- You want to keep material cost down: Swiss Krono Grey Oak is $2.49 per sq ft. Follow the manufacturer's installation humidity window when it goes in, and keep the hygrometer routine going afterwards.
If you live in a condo, check your building's own rules before you order.
Summer humidity FAQ for GTA homeowners
Does air conditioning affect hardwood floors?
Yes, and mostly for the better. While it cools, an air conditioner condenses water out of the indoor air, leaving less moisture for your boards to absorb. Trouble tends to start when the system sits idle on damp days or is switched off for a long trip.
What humidity should I keep hardwood floors at during an Ontario summer?
Start with the NWFA's general figure for solid wood, 30% to 50% RH, then check the manufacturer's sheet for your boards. Appalachian, for example, lists 35% to 55% for its solid flooring. Aim for the lower of the two upper limits.
How does humidity affect laminate flooring in Toronto homes?
Its fibreboard core reacts to the air around it, even when the top of the plank looks unchanged. Swiss Krono's German click-laminate instructions ask for 50% to 60% relative humidity while the floor goes in and for three days after. Once it is down, the same hygrometer checks used for wood floors show you when the room is drifting high.
Should I run a dehumidifier upstairs in summer?
Only if the hygrometer says so. If the AC keeps up, the upstairs reading may already sit inside range. If it stays above your floor's limit for days at a time, a portable dehumidifier in that room is a sensible addition.
Will a tight floor relax when the weather cools?
Ordinary seasonal tightness generally eases once the heating season dries the indoor air, because wood gives moisture back to drier air. Boards that stay raised once RH is back in range point to something other than summer air and deserve a closer look.
Talk to us about a floor for a humid room in Toronto and the GTA
Tell us which rooms you are planning, the floor type you like and what your hygrometer reads, and we will help you match a product to the space. You can request a quote online when you are ready.
Top Floorings Depot
3781 Victoria Park Avenue, Unit 1, Toronto, ON M1W 3K5
www.topfloorings.com
Call: 416-499-0117
Text: 416-770-8819