The building in question is a 1920s Philadelphia row home. The house has no insulation or vapor barrier. The roof has a 14″ cupola vent and a whirly bird vent, both located in the middle of the roof. 

I had planned to blow in 6-12″ of rockwool into the small attic, which would leave at least a foot of space for air movement above the insulation. I understand from reading the article about insulating residential flat roofs that condensation on the underside of the roof would be the prime concern with this strategy. I do plan on replacing my roof in 5-7 years, at which point I would insulate the exterior, but would like to make my house more livable during the winter in the meantime. 

Any advice is greatly appreciated. 
Best,