Ours is a detached 2 storey house with a problem - the upper floor heated up during the summer months causing the a/c to run constantly. Although it ran constantly, the upper floor was never comfortable, and was sauna-like causing us to decamp to the basement. We had several suggestions to "fix" the problem, including a roofing contractor who convinced us to add 5 more vents to the roof to vent out hot attic air. Several hundred dollars later, there was absolutely no change.
Reiner the reno coach then came in, measured the temperature in the attic on a warm day (65deg C, unbelievably), looked at the size of the a/c and the ducting system as well as the attic insulation before advising us to invest in reinsulating the attic. He provided a number of pointers, things to watch out for and companies for us to discuss with as well as an approximate cost.
We took a leap of faith and engaged a contractor to insulate the attic (separate review follows) using eco-friendly foam. The results were night and day. We were so convinced we had to add additional airconditioning, it was amazing to solve the problem the "right" way that improved the value of the property as well as kept our energy bills down both in the summer and in the winter. Thank you Reiner!