Humidity Level for Bamboo Flooring
A quick Google search found me this web page:

http://www.bamboo-flooring.com/bamboo-floor-maintenance.html


  14 Maintain relative humidity. Using a dehumidifier or humidifier to maintain relative humidity in the home at 30-50% will maintain the moisture level in the wood and help minimize cracks between the boards. Continued excessive humidity can cause swelling of the floor. Continued lack of humidity (below 20%) can cause shrinking of the planks and/or cracking of the bamboo strips.