When wood is exposed to different temperatures and different RH of the air it will either absorb moisture or it will lose moisture. Thus, with the changing seasons wood can absorb or lose moisture. EMC is Equilibrium Moisture Content. The EMC is what the moisture content of the wood will be when the wood will not lose or absorb moisture due to temperature and RH. RH has a much bigger effect on wood than temperature. Click here for an EMC table. The following are different scenarios that occur during the seasons. These changes will not affect the inside of buildings, when an HVAC system will keep the humidity levels within the acceptable range of 30-55%.
Summer, Hot and High Humidity:
With high RH and high temperatures wood will absorb moisture. Wood always wants to be at an equilibrium with the air. If there is a lot of moisture in the air the wood will absorb moisture until the EMC is reached; glue lines will fail, wood floors start buckling, etc.