In addition to utilizing tongue and groove paneling for your ceiling you can also install a raised panel ceiling and/or soffit.  This does not provide any substantial difference to your insulation value, but it does make a dramatic difference in the aesthetic look of your cellar.  Raised panel ceilings can be made to any room configuration whether it is a square, rectangle, octagon, or circle. 

To review the various ceiling options that Wine Cellar Innovations has to offer, please click on the following link:

www.winecellarinnovations.com/decceilings.htm