I have heard varying opinions on using cell foam on the interior of a roof. I understand that in most cases, there is a better way. However, I have a older home with a second level that was turned from an attic into a living space. There is no insulation at this time in my roof. I also do not have a ridge vent (as my house is from 1925) and no sofit venting to the outside of the house. AKA...absolutely NO ventilation right not! I want to install the cell foam and drywall over to make a cathedral ceiling. But, there are concerns of heat(I was told that this would not keep the heat from the roof out) and moisture that could cause mold.

Is it better to use the cell foam in this instance, or install the ridge vent, sofit vents, and put in those W shaped peices of foam (sorry can't think of their name) for air circulation with some other type of insulation before putting on drywall?

Any opinions are greatly appreciated.