Insulation should face the living space, with the vapor barrier (the paper or foil backing) towards the interior to help control moisture.
Insulation typically lasts 20 to 30 years, though some types, like fiberglass and rockwool, can last up to 50 years.
Spray foam insulation costs between $1,300 and $3,700 for a typical home, depending on the size and type of foam used.