Hardwood floor installation: this is how it should flow.
80% of the recommended practices for installing wood floors are to prevent problems later.
Some of these recommendations to install wood floors will seem annoying. We’ll try to explain why the annoyance is worth it.
Our reference text for all installation knowledge is the National Wood Flooring Association’s Wood Flooring Installation Guidelines updated in 2019.
All the steps here follow the National Wood Flooring Association’s installation guidelines. Stray from them at your own peril.
The following instructions assume installation of a solid 3/4″ floor (not an engineered or laminate floor) into a wood substrate over a dry basement or finished level.
If your floor is above a crawlspace, there must be a minimum of 18″ between the ground to the underside of the joists and the crawl space earth must be covered completely by a 6mil puncture-resistant black polyethylene film.
Is your subfloor good enough?
Solid, 3/4″ thick hardwood flooring needs to be attached to subfloor thick enough and solid enough to hold the fasteners through years of use and seasonal movement.
What works: historic (c.1880-1950) 1″x6″ or 2″x6″ diagonal pine planks
3/4″ thick pine plywood
What might work if you supplement with additional subfloor thickness: 5/8″ pine plywood, 3/4″ OSB
Nope, never: 1/2″ OSB, particle board
Time the wood delivery carefully
If you are installing the floor in a newly constructed space, be sure that the space is full enclosed and all HVAC systems are operating and at a habitable temperature and humidity BEFORE any wood flooring is delivered.
Deliver the wood to the space where it will be installed, not to the garage or basement – it needs to acclimate to its forever home!
This is because your wood needs to reach equilibrium with the moisture levels of the existing wood as they will be maintained when people are living there.
Use a moisture meter to test the moisture content of your wood and your subfloor. For wood less than 3″ wide it should be within 4 percentage points of the subfloor moisture. For wider boards, it should be within 2 percentage points.
The further apart the measurements are, the longer this will take. People may tell you that you should just wait a few days and then install, but if you don’t measure and you wood continues to dry out to match the conditions after you install it, the boards can gap and fasteners can be deformed, causing squeaks.
Details
Deliver the wood to the space where it will be installed, not to the garage or basement – it needs to acclimate to its forever home!
This is because your wood needs to reach equilibrium with the moisture levels of the existing wood as they will be maintained when people are living there.
Use a moisture meter to test the moisture content of your wood and your subfloor. For wood less than 3″ wide it should be within 4 percentage points of the subfloor moisture. For wider boards, it should be within 2 percentage points.
The further apart the measurements are, the longer this will take. People may tell you that you should just wait a few days and then install, but if you don’t measure and you wood continues to dry out to match the conditions after you install it, the boards can gap and fasteners can be deformed, causing squeaks.
Getting ready
While you are waiting for your wood to acclimate, you have plenty you can do:
- Make sure all quarter-round and baseboards are removed. Undercut your drywall if your intended trim is wider than the required 3/4″ expansion gap.
- Re-secure you subfloor to the joists with screws to guarantee the quietest floor possible. Grind down any obvious high spots with a sander.
- undercut trim at doorways so the the boards will look like they were installed before the casings were installed.
Determine if you need underlayment.
As of 2019, the National Wood Flooring Association updated its guidelines for what you need to lay down BETWEEN your subfloor and the hardwood floor.
The most important factor is what is BELOW the floor you are installing. If that area is a conditioned space, ie. you are installing in a second floor bedroom, or over a climate-controlled basement, you are no longer required to use underlayment of any kind.
But if you are installing over an unfinished basement or crawl space, NWFA advises a vapor retarder rated at xxx perms. This allows for controlled movement of moisture vapor through the hardwood to limit abrupt dimensional change. Aquabar B is a readily available commercial product that meets this requirement.
Rosin paper and #15 Roofer’s felt are no longer considered adequate vapor retarders under hardwood flooring!
Why can’t I just use plastic sheeting?
You don’t want to create a waterproof condensation point where water vapor from below will be trapped, causing mold and wood distortion. Slow, even progress of water through your wood keeps everything copacetic!
Determine board direction and starting point
Solid 3/4″ hardwood flooring should be installed perpendicular to your floor joists. This cross-bracing keeps your hardwood from sagging.
Alas, this means that if your new addition has floor joists that are not parallel to those in the rest of the house, you will not be able to run your new hardwood parallel to any of the older, existing hardwood, unless you add a minimum 1/2″ thick nominal plywood over the existing subfloor.
Consider your start point very carefully!
Details
Common wisdom suggests you should start on an exterior wall, but that may not always be the best place to begin.
The NWFA recommends starting at the most “aesthetically or architecturally” important point in the room because that will guarantee that the boards will be straight and square where you will notice it most.
This could could be at a fireplace, a kitchen island, or through an archway.
You can even begin in center of a room by snapping a straight, square starting line and screwing down some scrap lumber on that line to brace your first nailed course.
When you come back to do the other half, just unscrew your backer braces and use a piece of spline in the waiting groove to proceed tongue-first across the remainder of the room.
Whatever you do, don’t start on two different sides of a room, expecting everything to meet in the middle – you’ll end up ripping down odd-size boards right in the place that is hardest to hide your corrections.
Allow an expansion gap
Do not skip this! All wood continues to swell and shrink with seasonal moisture, not to mention unexpected water catastrophes!
If you install wood tight against your drywall or studs, even minor expansion magnified across multiple boards can cause enough pressure to pry up your fasteners and cause the wood to buckle off the floor.
In the actual words of the NWFA, “Unless specified by the manufacturer, the expansion space left against any vertical obstruction should be equal to the thickness of the material being installed.”
So, for 3/4″ thick wood, you need a gap of 3/4″ on all sides. Baseboards and base shoe are designed to cover this gap once the floor is sanded and finished. In places where you cannot cover a gap against a vertical obstruction (for example, masonry walls or sliding glass doors) use of cork of the same thickness as the flooring material is a tidy way to allow for expansion without a visible gap.
Rack out your wood
Your boards come in bundles of random-length boards. It is your job as the consumer to keep that pleasantly randomized pattern across your floor.
But the appearance of artlessness often takes great art. For example, don’t just install all your long boards in one section of the floor.
Details
Open multiple bundles and choose boards of alternating length, cutting out minor flaws as necessary, and trimming to fit the row while minimizing waste.
Most professional contractors will rack out 6-8 rows and nail those down before racking out the next 6-8 rows. Be sure to stagger your board ends by a distance of 2-3x the width of your material.
Don’t try to form regular “stair-step” or “H-pattern brick courses” as you install. The distribution of board ends should appear organic and natural.
Did you get some fabulous quartersawn boards in your bundle?
Install those center stage where you will see them. Wonky boards, plain grain, or shorts? Save them for your ending rows where the couch will cover them.
Get it nailed (or stapled) down
Everybody asks if cleats are better than staples for securing a hardwood floor. The NWFA approves both. If you are installing a hard, brittle wood like Brazilian Cherry or other exotic, cleats can reduce cracked tongues.
But for all American hardwoods, both staples or cleats are appropriate, but they should be at least 1 1/2″ in length. All fasteners for standard hardwood floors are “blind-nailed” which means they are nailed at an angle right into the tongue side of the board, which makes them effectively invisible when the floor is complete.
We recommend using a pneumatic stapler or nailer – no need to be a hero by insisting on using a manual version.
Details
You are likely to get more misfires AND hurt your shoulder into the bargain. However, you are likely to hand-nail the first row or two into the tongue because the nailer won’t fit tight to the wall.
You will have the same issue with your final rows as well, and because you won’t even be able to get a hammer and nail into the space close to the wall, all last rows and top-nailed and countersunk.
The nailing schedule should be every six to eight inches, aiming for the joist where possible, using at least two fasteners per board. Be careful not to nail too close to the end of a board – this can cause splitting. Keep that last staple at least 1″ from your end-joint.
Set you compressor so that it drives the nail or staple just into the nail pocket. Too deep and tongues can split, but too shallow and you won’t be able to fit the next board’s groove over the protruding fastener.
Pete’s Bonus Tips
Three installation definitions
End-matched
When even the short ends of hardwood flooring are tongued-and-grooved. This creates a superior holding on all four sides of every board. This is important because seasonal change can cause hardwood to change in both width and in thickness.
Board width change just creates gapping, but even a slight lift at the end of a board can create enough lippage for you to catch a toe! It also exposes that board end to chipping.
End matching keeps those short ends tight and level. Conventional milling puts a tongue on the north and east side of every board and a groove on the south and west edges.
Blind-nailed
When tongue and groove flooring is nailed at the tongue of each board, allowing the adjacent board to cover up the fastener, which means the floor is secured almost invisibly to the subfloor.
Even more important, the nails are at least a 1/4" from the surface of the boards, which makes for a much less risky sanding experience.
Top-nailed floors are a beast to sand because all your fasteners must be counter-sunk by hand or they might catch the sanding drum.
Relief groove
There is endless debate about the purpose of these grooves that are milled into the back side of hardwood flooring. The best explanation we've heard is that the grooves prevent the board from becoming "case-hardened" during the drying process.
This keeps the board from developing shinkage-induced interior stresses that would cause cells in its core to buckle and collapse. For the rest of us, the relief grooves tell us which is the face side of the board.
Spline (slip-tongue)
A narrow strip of wood that can slip into the groove of a piece of hardwood flooring and turn it into a tongue.
Because tongue and groove floors are always installed tongue-forward, spline allows you to change your installation direction in irregularly-shaped rooms.