Plank Floor: What Special Considerations This Type of Floor Raises
My definition of a plank floor is anything 4" and wider. One of the biggest mistakes I see in the wood floor industry is the failure to treat plank floor like the special item it is. And the very worst kind of plank floor is the prefinished wide boards. If you are thinking about installing a wide plank floor read this article carefully, and consider if this product is worth the trouble for you. In the North East here we have hot and humid summers, and then,heat our houses to desert dryness during the winter. So be sure to install the 4" and wider boards in the manor I describe below. In some very moisture stable climates, 4" boards may be still OK to install like strip floor. But don't try to get away with a simple nailing when you go wider that 4", you'll regret it no matter what climate you experience. In any climate you must try to keep the relative indoor humidity within 40-60% if you want minimal movements of these wide boards.
With a sharp increase in humidity (30% or more) the 4" board will expand twice as much as the 2" one. These wide boards will exert tremendous pressure against each other. They can actually crush each other slightly and push out along the sides of the floor into the expansion spaces (hopefully provided). The floor will remain tight until the winter heating season sets in. A lot of homes are heated very well but no humidity is added to the air. A simple attachment to the furnace duct will provide this with a forced air system. Or you can get various portable humidifiers and put them in several locations. The prefinished floors are more subject to moisture changes because they are not sealed in any way on the many seams. The best thing one could do with a prefinished plank floor would be to recoat the surface several times after it has been installed. It sort of defeats the purpose or prefinished, and you may also find that these durable conversion finishes are difficult to get any kind of finish to stick to them.
THE FOLLOWING DESCRIPTION OF SUBLFOORS ASSUMES THAT YOUR SUBFLOOR RESTS ON 16" CENTER TO CENTER JOISTS. IF YOU HAVE ANYTHING UP TO 24" BETWEEN THESE JOISTS YOU MUST ADD ANOTHER 1/4" OF PLYWOOD. THIS WOULD BE BEST DONE IN 1/2" LAYERS TO GIVE THE FULL STIFFNESS OF THE PLYWOOD. AND A URETHANE ADHESIVE NEEDS TO BE SQUIGGLED BETWEEN THESE LONG SPANNING JOIST ALSO. FAIL THIS AND YOU WILL HAVE A SQUEAKY FLOOR IN A FEW YEARS.