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

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.

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

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How hardwood floor installation actually works

1. 1

   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 forSolid 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.

2. 2

   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 forA 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.

3. 3

   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 forAcclimation done in a garage, a basement, or a house that has not had HVAC running. It achieves nothing except the appearance of due diligence.

4. 4

   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 forStarting 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.

5. 5

   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 forAn 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.

6. 6

   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 forFasteners 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.

7. 7

   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 forGaps 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.

8. 8

   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 forSite 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.

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 →

If the number is the problem, here are the ways people pay for it →