We created an isulated room inside of our already well-insulated building for our barrel room.  We wanted to keep our bottled and barreled wines in a climate controlled enviroment to best protect the wine and allow aging to occur without large temperature swings.  
     We also installed a commerial sized humidifier called an AquaFog that controls the humidity of the room.  We like to keep the barrels at about a 60-65% relative humidity.  We knew that if we didn't spend the extra time and money, we would lose over 10% of our wine in evaporation alone, especially due to the extremely dry air in our high desert Arizona winery.
     Also, controlling the humidity in the barrel room helps to keep the wine inside the barrels closer to the state they were when we barreled them for aging.  Well that's a confusing mouthful.  Basically, if the storage atmosphere is too dry, then water will evaporate through the wood, causing two things to happen: the percentage alcohol increases and  the air space inside the barrel increases.  Both can be a problem.  I like to keep the wines under about 14.5% alcohol, so increasing the percentage while aging is a problem.  The air space created inside the barrel, called ullage, is potentially a huge problem since after fermentation is complete, oxygen is NOT the winemakers friend.