I have read through virtually every article and post here as I prepare to install approximately 500sq ft of bamboo flooring in my townhouse. I have read the numerous posts that are related to moisture problems. I'll describe my situation:

5/8 x 3.75 approx x 37" bamboo flooring.
23/32 T&G plywood subfloor.
2nd floor with finished heated laundry/storage room below.
I plan on using 15# roofing felt, 1.5" staples and a MIIIFS.
install woll be perpendicular to floor joists.
Washington, DC area

I don't believe I will have an excessive moisture problem as so many people seem to have had when installing over concrete, but I am worried about the fact that it is so dry in my house right now. I'm picking up an ambient air moisture meter tomorrow to get a reading....but I know it's dry. The bamboo flooring has been acclimating on the 2nd floor in the room where it will be installed for 5 days now, and it will be at least 5 more before I start the project. My concern is that I'll get everything installed while it is very dry, and things will expand as the humid summer months set in. Do I have to worry about the much higher moisture in the ambient air during the summer months (house will be air conditioned when temps are above 82).? Or will the subfloors and the bamboo expand at a similar rate as they draw in moisture?

Thanks for all of the great info I have found here!!

It has been repeated here often. You need to be between 40 and 60 % relative humidity. That is what is important. It's ok to have the occasional peak above or below but for the most part, it needs to be between those numbers. Time of year doesn't matter. It's the indoor climate that matters. You may need a humidifier. 45% to 50% relative humidity is ideal. Strangely enough, that is what it is in my home almost all the time and I don't make an effort to get it there. I have forced air heat but only set it on 68 degress and air conditioning for the summer which I will use often. And the interior relative humidity stays right around 50% all year round. Guess I'm lucky. I know it gets major humid back east. I can't tell you what to do. I can only tell you what is needed. Your decision.

The time of the year deal was before we all had climate control systems in our homes. Forced air or radiant heat and AC.

No matter where you live houses will vary depending on how the regional climate, how tight your house is and whether or not you even run the HVAC year round. Some people are able to keep the house opened up for months at a time.

Investing in a thermometer/hygrometer is a wise decision for anyone that has hardwood floors. I have people tell me they can't find them. Look in the outdoor section of a big box store where they stock the thermometers and patio furniture. Walmart and Radio Shack sell them too.

Right now where I live it is in the 20's outside. Inside it is 72 at 50% RH. I have gas forced air heat with no humidifier. I can't figure that out either, but my house has never needed any help with the RH range.

I looked at a bamboo failure this week and took the lowest reading I have ever seen in the interior of a home here in central Texas... 26% rH

They were wondering why the cupping and cracking of their bamboo.

Thanks for all of the help. Finally was able to track down an RH meter today...seems like a seasonal item around here as I had to look for it in the clearance sections at the box stores....and it's a good thing I got one! After letting it settle in for a few hours I was at 27%. I've got the new humdidifier up and running now, and I'll wait until I have 40% or above for a few days prior to starting. My wife thinks I'm nuts for how fanatical I have become with following all of the advice on here, but I think I have already avoided many of the common errors. Thanks again for all of the great info!!

I have to run a humidifier almost all winter, it probally has to do more with the crappy windows I have that are about as efficent as a paper bag than anything. But Even in my office the rh during the winter wants to stay down around 25 to 30%.