The deal moisture content, what your calling humidity(humidity is moisture in vapor form) is exactly the same, and real close to what the average moisture content is for your region of the world. And there is a limit for both subfloor and flooring, or mold is a big concern.

I shoot for the regional average moisture content, which is 9% in my area of central Texas. If I see a subfloor with 12% or higher, I will not install at all. That is a red flag, here.

The rule is 4%MC difference with strip flooring, and 2%MC for plank and any exotic floor. But a 8%MC 2¼ wide board, installed on a 12%MC subfloor, is asking for trouble in my book, unless you leave some minute calculated gaps between each row of flooring.

If the HVAC is not up and operational, running to efficiently condition the home, not set at 80º during the summers, or 80 during the winter. You want the HVAC to run efficiently during the summer, to pull any building up of the humidity levels inside the home. With todays home building practices, homes are built much tighter than those just 10-15 years ago, much less 50 years ago. So those tight building practices, actually create a greenhouse out of the home, if there is nothing running to remove the building humidity or even air circulation.

Then in the winter you have the heater drying all the wood out, and an air tight home. Your making a kiln. Unless you have something to add moisture into the air, to create higher humidity levels inside the home, the wood will dry out and shrink in dimensions across the face of each board. It can be extreme, depending on the wood species.

So, all in all, it sounds like the guy holding up your investment truly cares about what he or she is doing. It sounds like they know what they are talking about, instead of some salesman, telling you what you want to hear. They are not out to make the fast money and run from the problems later. Not every project is the same as another, even if they are the same floor plan, built right next door to each other.

Thanx for the insight. Should. E installing the AC next week. Planks are at 5.5% and subfloor is at 12% so we have a little ways to go. Thanks for explaining.

I have just had installed an engineered wood floor. It is a good floor. A patina relics distressed red oak. The company that installed my floor did not put in an expansion gap. They did not pay heed to the installation guide. now they are trying to tell me my subfloor has a moisture problem. The old subfloor has a good reading.... very good. The new subfloor put on the old in the living room has been there for three months prior to install. It was screwed down and not squeaking. The company is telling me it reads 16% and i am definitely not geting that reading at all. I had someone else measure the subfloor and they did not get that reading either more like a 9%. The flooring itself the company is telling me is 7% but when i took a moisture meter to it and this independent flooring guy took his delmholst meter to it the engineered floor has unstable readings all along the side of the plank...along the tongue side. This is a tongue and groove flooring with a sliced veneer. So i have an improper installation...now i am being told moisture levels are a problem.... what is the proper moisture level for both the subfloor and the engineered floor? I chose this flooring due to its stablitly and it ability to handle changes in humidity. I asked for the company to come in and inspect... they did not do a good job of that ...and now i find no expansion gap. What will happen now if the floor has no space in which to expand?

Is this also an issue with installation of laminate flooring (Armstrong Grand Illusion) if you use the moisture barrier and premium underlayment?