Hello everyone,
Great site!!
This is my first post here. We are from Vancouver, Canada. English isn't my mother language, please forgive my grammer mistake.
Weather is quite wet here in Winter and Spring. Summer is very pleasant. Humidity is around 70-80%.
We plan to install prefinished hardwood floor this Summer. It is for the upstair. Since we have no plan to move for at least another 10-15 years, we don't mind to spend a bit more in order to have it done to the way we like.
The existing floor is carpet on 5/8" plywood. I want to add another layer of 3/8 ply so that I can run the plank in any direction I want, get more solid feel, less resonant when walking on it and minimize the chance of sqeaking in the future. I have two installer gave me the quote but at the same time, both insisted that extra 3/8 ply is unnecessary. I can sense both installer don't want to deal with the door clearance, re-install the newel and railing. They just want a quick in and out.
If I put another sheet of 3/8, my first question is do I have to worry about the moisture content of those plywood? Does it need to be acclimatize as well? If yes, how long is the period is considered sufficient?
Next question, a side one, someone told me never paint the house while installing wood floor at the same time; it is because the moisture release from the paint can be absorbed by the wood, especially those laying around for acclimatizion or waiting to be install? Is this claim legit?
Thanks in advance for the answer.
Wal

To answer the two salient questions you ask; yes, the new plywood underlay becomes part of the overall structure of your floor system, and as such must be acclimated to the site. It is not a question of time alone; it is a question of moisture content equilibrium and could take anywhere from a day or two to several weeks. This is dependent on the MC variation of the products being used combined with site conditions.
While it is true that all wet trades (including painting) should be done prior to arrival of the hardwood, some practical common sense must be applied. Do you plan on never repainting the house over the next 10-15 years? But in general, yes, do your painting first, since there is less risk of damage to the floor by ladders, spilt paint, etc.

I do not understand the hesitance of the contractors you have spoken with to want to add the plywood underlay and the extra side work (door shortening, railings, etc.) that that will entail. Perhaps you need to talk with a general contractor who relys on this sort of work to make a living if qualified flooring people arent available who can do these things.
Certainly, we like all the extra work that sometimes need to be done, since it gives us additional funds to enjoy our time in Las Vegas.