Racking Hardwood Floors
For nail down installations over a wood subfloor racking becomes time saving and gives one a better idea of 
the overall color and appearance of the installation. Racking is defined as laying out the floor before it is nailed. I've seen some professionals that would pull one piece at a time from boxes, put it into place and nail it home. This is very time consuming and you will not get a good color and length mix.
Allows For Good Color Mix
There's nothing worse than looking at a brand new 
installation with dark and light colored boards bunched across the floor. The same holds true with poor distribution of lengths as nearly all solid hardwoods are manufactured in random length. Racking will prevent bunching of smaller pieces in one area, providing one keeps an eye out for it. Generally we prefer to select from 4-5 bundles or boxes of hardwood as chances are good you may run into light and darker colored bundles.
Big Time Saver
Other benefits of racking if you run into an angled wall is precutting the angles, instead of making dozens of trips back to the cutting area. Racking also allows for final inspection of the flooring for finish quality and milling before the actual fastening. Sometimes you cannot see every flaw on the floor, but looking from a standing position is likely to provide a better view. Keep in mind, if any defective hardwood is installed, no manufacturer will consider it a claim, nor is it covered under warranty. It is the installers responsibility to 
perform final inspection.
Our second image above shows a prefinished American Cherry that has been racked out to fill an area up to the wall line. By using 4-5 boxes you not only get the color and grain variation, but the lengths are mixed accordingly. Avoid bunching smaller and larger pieces as well; they should be placed at random. End joints should be staggered as far apart as possible but six inches seems to be a preferred minimum among professional installers for products three inch wide and less. For wide plank floors the spacing should increase. End joints should not be repeated with subsequent rows.
Unfinished Floors
For unfinished wood floors, attention to color mix should be more pronounced. While some pieces may look borderline in color, it's probably wise to toss them aside. Once any finish is applied they can really stand out.
Most hardwood installers prefer the use of #15 asphalt felt paper that is laid down on the subfloor prior to racking. Asphalt 
felt or standard roofing paper provides a few benefits with those being a moisture retarder and in some cases can suppress squeaks. It should be laid out parallel the installation and overlapped four inches on the seams. Racking should be done from the left to the right of the layout if your right handed, but can be reversed if starting from an irregular wall (makes for easier cuts).
Reverse Boards at Wall
When reaching the other end while racking it is not necessary to measure each board to fit. Simply reverse the board where the tongue and tongue are facing each other and loose lay it in that area. This is also good method to save on material by utilizing as much as possible.
View My One Minute Quickie Video
With the tongue against tongue method, make sure the end piece is butted to the stopping area (baseboard/drywall) and place a pencil mark where the cut will be. For solid material a good rule of thumb is to allow enough expansion equal to the thickness of the product. For smaller layouts, 3/4" expansion is not necessary, but wise to keep the habit of doing so.
Exception to Underlayment
In the case of solid 3/4 inch wider plank being used in areas susceptible to high humidity and moisture, many professionals opt for the glue and cleat nail method of installation instead of using asphalt paper. Gluing with a quality subfloor adhesive or Bostiks Best will hinder cupping of wider material.
Rosin Or Felt Paper?
Floor Nailer
Nail Guns
for tough to reach areas
