P. S. Room is not heat. We are going to in stall a gas or electric fireplace for on occasional use.

Hi Donna,

Thanks you for the compliment!

Really not sure about the "context" in which this information was given. Here in the south, attaching (nailing) tongue and groove flooring to a plywood or OSB subfloor is standard practice. Our biggest challenge is moisture, most typically seen when the flooring is subjected to high humidity, which can occur under multiple circumstances, often seen when installing wood flooring that has an excessive moisture content. In this application, a water vapor underlayment 'paper' was put over the plywood floor before the wood flooring was installed to prevent water vapor from penetrating the wood flooring from below, the deck itself is open which allows maximum airflow. The pine will be more tolerant to "movement" than for example an oak floor.

Regarding tile or stone, certainly weight and structural support is a concern. But more important is that the mortar and grout is not pliable, and so any "movement" will result in cracking, which can be caused by insufficient structural support and also rapid temperature fluctuations i.e. (warmed by sun and cooled rapidly at night. The gas fireplace could also cause excessive drying of the wood, but this is the case with gas heating in an indoor environment.