Flooring · Service

Hardwood floor installation, and the humidity it has to live in

Solid wood is a material that moves for its entire life. A good installation is really a set of decisions about how it will be allowed to move — acclimation, expansion, fastener schedule, direction.

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In short

What is hardwood floor installation?

Hardwood floor installation is the fitting of solid wood boards, normally by nailing or stapling them through the tongue into a wood subfloor. The board is real timber all the way through, so it expands and contracts with humidity for as long as it exists. Getting it right is mostly about moisture — the wood's moisture content at install, the subfloor's, and the humidity range the house will actually see.

Triggers

Signs you need hardwood floor installation

You are pulling up carpet and have found original wood underneath in poor condition
You want a floor that can be sanded and recoated decades from now instead of replaced
You have a wood subfloor over joists, over a conditioned basement or crawl space — the conditions solid wood likes
You are matching or extending existing hardwood into a new room or an addition
You are replacing a floor that has already been refinished as many times as it can take
Resale is a factor and buyers in your market visibly price real wood differently

Seeing something not on this list? Browse flooring problems by symptom →

The job

How hardwood floor installation actually works

Confirming the floor is a candidate for solid wood

Solid hardwood wants a wood subfloor and a space that stays within a normal humidity band year-round. Below-grade basements and slabs are engineered-wood territory, not solid-wood territory.

Watch for: Solid wood proposed over a slab. It can be done over a properly prepared plywood sleeper system, but that is a different, more expensive job and should be described as one.
Moisture readings — subfloor and flooring together

The installer meters the subfloor and the flooring itself and compares them. The gap between the two, not either number alone, predicts whether the floor will gap in winter or cup in summer.

Watch for: A single reading, or no reading. Wood delivered from a cold truck into a heated house has not equalised, and installing on that day builds the movement in.
Acclimation in the finished space

Boxes are opened and the material is stacked in the rooms where it will be installed, with the house at normal living temperature and humidity. How long depends on the species, the format and how far apart the readings started.

Watch for: Acclimation done in a garage, a basement, or a house that has not had HVAC running. It achieves nothing except the appearance of due diligence.
Subfloor preparation and underlayment

Panels are refastened to stop squeaks, high spots sanded, low spots filled, and an underlayment or vapour retarder laid depending on what is below the floor. Layout lines are snapped from a straight reference, not from a wall.

Watch for: Starting lines taken off a wall. Walls are not straight. A floor started off a bowed wall runs progressively out of parallel and the error shows up as a wedge at the far side of the room.
Direction and racking

Boards run perpendicular to the joists as the default structural rule. Before fastening, the installer racks several rows out dry — laying boards from multiple boxes to distribute colour, grain and length so the floor reads evenly rather than in stripes.

Watch for: An installer working straight out of one box at a time. Batch colour variation is real, and a floor installed box-by-box ends up with visible bands across the room.
Blind nailing through the tongue

A flooring nailer drives fasteners at an angle through the tongue so they are hidden by the next board. Fastener spacing follows the manufacturer schedule, tightened near board ends where cupping starts.

Watch for: Fasteners spaced wider than the manufacturer calls for to save time. Under-fastening is invisible on day one and shows up as movement and squeaks in year two, and it is a warranty argument you will lose.
Expansion gaps at every perimeter

A gap is left at all walls and fixed obstructions so the floor can grow across its width in humid months. It is covered by baseboard or shoe moulding, not filled.

Watch for: Gaps caulked, filled or omitted at a hearth, a stair stringer or a kitchen island. Any one of those pins the floor and the pressure has to go somewhere — usually a buckled row in the middle of the room.
Finish — prefinished versus sanded on site

Prefinished boards arrive coated and the floor is usable immediately, with micro-bevelled edges you can see and feel. Site-finished floors are installed raw, sanded flat and coated in place, giving a seamless surface but adding days and dust.

Watch for: Site finishing scheduled with other trades still working in the house. Dust in a wet finish coat is permanent, and there is no fixing it short of sanding the floor again.

Money

What does hardwood floor installation cost?

Solid hardwood installed is typically among the higher-priced flooring choices per square foot, with species and board width driving material and site finishing adding labour days over prefinished. Subfloor correction and stair work add separately. The Cost Guide breaks the ranges down properly.

See the full hardwood floor installation cost guide — by material, size and region →

Straight answer

When hardwood floor installation is the wrong call

Everyone else ranking for this is paid when you say yes. Here's when you shouldn't.

You are installing below grade. Basements move through humidity swings that solid wood cannot tolerate. Engineered wood, which is dimensionally stable across a plywood core, exists precisely for this and looks the same underfoot.
The room is a bathroom, laundry or entry that gets standing water. Solid wood and repeated wetting do not coexist. This is not about a spill wiped up; it is about a floor that is regularly wet at the perimeter.
Your house sits empty and unconditioned for months. Seasonal homes that go unheated or without dehumidification swing far outside the humidity range solid wood is warranted for, and the resulting gapping and cupping is not a defect claim.
You have large dogs and want a flawless floor. Softer species dent under claws, and no finish prevents it. Either choose a harder species and accept some marking, or pick a material with a wear layer built for it. A refinishable floor is repairable — but "repairable" is not "won't mark".
Floor height is fixed by an existing threshold, appliance or stair. Solid wood plus underlayment adds real height. Where the top step of a stair or the gap under a dishwasher will not accommodate it, a thinner material saves a cascade of modifications.
You need the room back tomorrow. Between acclimation and, if site-finished, sanding and cure time, this is the slowest common flooring installation. If the schedule is the constraint, prefinished engineered or plank gets you there faster.

Your options

Types of hardwood floor installation

Solid vs engineered hardwood

The decision that comes before this page — worked through in the Comparisons archive.

Wood material guides

Solid hardwood, engineered hardwood and bamboo, species by species.

Board layouts and patterns

Straight, diagonal, herringbone and chevron — each changes labour and waste materially.

Wood floor colours

Light, medium, dark, whitewashed, oak and walnut tones.

Compare flooring options side by side →

Straight answer

Can I do this myself?

Reasonable to DIY

Removing old carpet, pad and tack strip, and pulling staples out of the subfloor
Refastening loose subfloor panels to the joists to kill squeaks before the wood goes down
Stacking and acclimating delivered material correctly in the right rooms
Removing and labelling baseboard for reinstallation

Call a licensed pro

The nailing itself — a pneumatic flooring nailer at the wrong angle or pressure splits tongues and the damage is under the next board
Establishing the starting line and keeping the floor parallel across a long run
Racking for colour and length distribution, which is judgement more than technique
Stairs, thresholds and transitions where hardwood meets anything else
Any on-site sanding and finishing, which is a separate skilled trade from installation

Before you sign

What to check when hiring for hardwood floor installation

What moisture readings did you take, on what, and what were the numbers?

Two readings — subfloor and flooring — and the gap between them. This is the core of a hardwood warranty claim later.
How long will the material acclimate, and where?

In the rooms, at living conditions. A specific answer here separates installers who have read the manufacturer instructions from those who have not.
What fastener and spacing schedule are you following?

It is published by the manufacturer for each board width. An installer who can quote it is following it.
Which direction will the boards run and why?

You want to hear joist direction in the answer, not only aesthetics. Both matter; only one is structural.
Prefinished or site-finished, and what does each do to my schedule?

The difference is several days and a very different amount of dust in your house.
How are you handling transitions to tile, carpet and the stairs?

Stair nosings and thresholds are skilled, fiddly and routinely left out of quotes.
What humidity range does this floor need me to keep, year-round?

Every hardwood warranty specifies one. If nobody tells you the number, you cannot comply with it.

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Local pros

Hardwood Floor Installation near you

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Related work

Often done at the same time

Floor Refinishing

The alternative if the existing wood is salvageable

Subfloor Repair

What has to be sound before nailing starts

Flooring Installation

The general process across all materials

Floor Removal

Getting the old floor out first

All flooring services →

FAQ

Hardwood Floor Installation — questions people ask

Still have a question? Talk to our team →

How long should hardwood acclimate before installation?

Long enough that the flooring and the subfloor readings converge — which is a measurement, not a fixed number of days. Manufacturers publish minimums, and wide boards and unusual species generally need longer. The condition that actually matters is that the house is running at normal living temperature and humidity throughout, otherwise the clock is not really running.

Can solid hardwood be installed over concrete?

Not directly. It requires a plywood subfloor system fastened or glued over the slab, with a moisture barrier, which adds height and cost and needs the slab tested first. Where a slab is involved, engineered hardwood is usually the better engineering answer — same wood surface, far less movement risk, and it can often be glued directly.

Why does my hardwood floor gap in winter?

Because indoor air is drier in heating season and the boards shrink across their width. Some seasonal gapping is normal and closes again in summer. Gaps that stay open year-round, or open unevenly across a room, point to installation moisture problems or a humidity range outside what the floor was warranted for. Whole-house humidification is the usual mitigation.

Prefinished or site-finished — which is better?

Prefinished is faster, lower-dust, and the factory finish is generally harder than anything applied on site; its trade-off is a visible bevel between boards and a slightly less seamless look. Site-finished gives a flat, continuous surface and lets you match an existing floor exactly, at the cost of days of sanding, coating and cure time in a dusty house.

What board width should I choose?

Wider boards read more contemporary and show off grain, but they also move more across their width, which means more visible seasonal gapping and generally tighter installation requirements. Narrow strip is the most forgiving. If you want wide boards in a climate with big humidity swings, engineered construction is worth serious consideration.

Do I need to remove the existing floor first?

For nail-down solid hardwood, effectively yes. It needs to be fastened into a sound wood subfloor, and going over an existing finished floor both raises height significantly and hides whatever is happening underneath. Removal is a real line item — make sure it is priced rather than assumed.