As an electrician, I design homes to be energy efficient. Most builders are concerned about the bottom line and not energy efficiency. I had a customer call me wanting to purchase a generator. But in talking to him about his needs he complained that his house was hot. So he thought if he updated his roof to a metal roof, it would keep that heat out. First of all, don’t put a metal roof directly on top of another roof. If you are going to leave the existing roof in place and put the new roof on top of it, there should be space in-between the old and the new. There needs to be air between the two for penetration. Don’t add a roof to dissipate heat. It won’t work. You must raise the new roof above the old. That’s what helps the heat dissipate.
Since the homeowner tried that and it didn’t work, he thought he needed a bigger air conditioner. That’s not the way to go. Don’t increase the size of your air conditioner; increase the efficiency of your house. If you have heat coming in, address the heat problem. Don’t address it by trying to increase your air conditioning bill. Do you want another high bill?
Best thing to do is decrease heat that is coming into your attic. One way to do this is by using foam insulation or foam board in your attic. You need something to decrease that heat penetration into your home. If you can decrease that heat penetration, you can go to a smaller unit and decrease the size of your air conditioner. How do you keep heat out of your house?