I'm renting a house that was never originally intended to be occupied full-time. The house is of a cinder block type construction with no insulation in or on the blocks. The attic has some insulation, but only at an R-value of 9. I'm fortunate that I have free natural gas on the property for heating - so heating isn't an issue. However, in the summer the house is unbearably hot and difficult to air-condition with two portable AC units (the windows are an unusual size and won't allow for a standard window unit.)
Edit: I'm in climate zone 6a in central West Virginia. The attic currently has a ventilation fan that I ran around the clock last summer.
Would increasing the insulation in the attic likely make a noticeable difference in cooling the structure in the summer?