I have a house that was built in 1903 and is balloon framed. I have been slowly renovating and updating the house with all new electrical, plumbing, adding a bathroom, installing ductless heat pumps,etc. and am getting close to the end of the major projects. My attention will then be on the walk-up attic. The attic is floored with planks and there is cellulose installed under the planks. We use the space for storage and given the complications and limited floor joist depth(8″ ) I am thinking that foaming the roof would be the best way to cut down on air movement and increase insulation values. My question with this is whether or not I will need to actively condition this space or if the rest of the house will keep it reasonable. The space is about 900 square feet but the average height is only about 5′. 
Any input would be welcome.
Thanks