You will need to make a decision on how thick your want your insulation installed. Foam insulation r value is typically higher than your standard batts of fiberglass insulation. You will need to check the recommended r value ratings in your area to find out how much thickness you will need.

As for installing foam insulation in the attic, you are going to have to be careful. The best place to spray foam insulation in the attic is on the underside of your roof. This will provide for a very comfortable attic space and increase the efficiency of any heating or cooling equipment that might be stored in the attic. However, you need to remember that the attic is often the only pathway for excess interior water vapor to leave your home. You will want to make sure that your installer is using an open-cell variety of foam insulation so that water from leaks can pass through and avoid being trapped against the wood roof sheathing and lumber. An attic fan is also an option that you might consider if you don’t have one to improve ventilation in the attic space.

Since foam insulation is generally more expensive than fiberglass or cellulose insulation, it is important to figure out if this route makes financial sense. If you can get the same amount of r value in one of the cheaper materials, you will end up with the same efficiency so it makes little sense to pay more for the same benefit. You must also keep in mind that r value does have a diminishing marginal return. In other words, the more you get the less each additional unit of insulation increases your efficiency. You can go overboard! Consult with your HVAC contractor and come up with a plan that makes the most sense for your situation.