Installation: this is how it should flow.
80% of the recommended practices for hardwood installation are to prevent problems later.
If you ask enough people, eventually someone will tell you that you don't need, for example, to use a vapor retarder under a hardwood floor. But always consider your source.
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.
Wait to deliver
This may seem obvious, but don’t even deliver hardwood flooring to your site until your space is finished, enclosed and all HVAC systems are operational (and definitely don’t install while they’re power-washing the basement or mudding sheetrock in the adjacent rooms because your flooring will want to absorb all that water).
Do not install any wood until the temperature and humidity in the space have reach levels that will be maintained during
Get the bundles of hardwood flooring into your install space so they can acclimate well ahead of your install date. Open up at least half of the bundles to expose more of the wood surface area to the air.
Acclimation is not measured in TIME, so don’t ask how many days before you can start nailing your boards. You must wait until the moisture percentage of the new wood, as measured with a moisture meter, is within two percentage points of the measured moisture of the subfloor. Rent our moisture meter! We rent a pinless moisture meter which does not damage your wood.
Remove trim then undercut if needed
Take off all the quarter round and the baseboards and undercut your doorway trim so that your flooring will slip under it neatly. And yes, if you have those cast-iron radiators, you will need to temporarily remove them or find a way to install under them.
Resecure your subfloor to the floor joists with screws to guarantee the quietest floor possible.
Install roofer's felt
Use a hammer-tacker to cover the subfloor with 15lb roofer’s felt as a vapor retarder. Never use sheet plastic because this will hold moisture against both subfloor and finished floor and encourage mold growth. If you start laying paper at your starting wall, overlapping it about 3", you can slide your boards on the paper and they won't catch on the paper's edge.
Unfinished and factory-finished ¾” solid hardwood should be installed perpendicular to the joists or, if your subfloor boards are diagonal (fairly common in those pre-1920s houses) perpendicular to the joists OR perpendicular to the subfloor direction. Hardwood floors that are installed parallel to the joists will eventually sag between those joists; if you insist on changing the recommended floor direction, add a minimum ½” nominal plywood underlayment to the existing subfloor.
Determine where to start
Consider your starting point very carefully! General wisdom suggests that you should start on an exterior wall because it is likely to be the most square, but that may not always be the best point to begin.
The National Wood Flooring Association installation guidelines say to, “choose a starting wall according to the most aesthetically or architecturally important elements in the room, taking into consideration fireplaces, cabinets and transitions as well as the squareness of the room.”
Ask yourself where your eyes are drawn when you first enter the room from its main doorway. Starting at that point will ensure that that the eye encounters straight, whole boards where it matters most. Consider burying your final boards, the ones most likely to ripped down on the diagonal and be top-nailed, on walls where there will be furniture or other distractions.
You can even begin in the middle of the room or at a center island; just be sure to snap a straight, square starting line and screw down some scrap lumber to act as a brace so that your first nailed course doesn’t slowly migrate with each blow from the nailer.
When you need to nail the other half, you’ll remove the temporary backer boards and use a nifty piece of spline to, voila, turn the groove side of the already-installed board into a male, tongue-forward starter board.
Know your expansion space
Allow a 3/4" expansion space around the perimeter and all vertical obstructions. Yes, you really must do this: if your boards swell and your room is twenty feet wide and the boards are already pressed up against your wall studs, those puppies are going to lift up like drawbridges. Scrap 3/4" hardwood makes a great temporary brace/filler for your expansion gap; just stand it on its groove end against the sheetrock.
Top-nail and blind-nail the first row (hand-nail if necessary). Denser species can be brittle, so you may have to pre-drill your holes for hand-nailing. Each succeeding row should be blind-nailed with your nailer/stapler wherever possible. At the finishing wall, it may be necessary to blind-nail by hand until top nailing is required.
Laying out the boards
Your wood bundles will contain boards of all different lengths. This is a good thing because you want your floor to look evenly random when it’s done.
You do NOT want it to look like a bad siding job where all the boards were the same lengths so all the joins ended up in a neat line. You need to stagger your joints at least 6” apart in adjacent rows and at least 3” apart for joints that are two boards away.
If your boards are wide, increase this spacing by at least 50%. You’re trying to keep the floor from looking like a regular brick wall and staggering your joints carefully will help avoid those “H” patterns.