The Building Performance Institute (BPI) is the nation's leading building science accreditation organization. It hinges on the philosophy of a house as a system, which looks at a building's various components (building envelope, attic, basement, combustion equipment, climate, occupants, ventilation sources) and the interrelationship among them to maximize a home's performance. This approach leads to greater energy efficiency, but perhaps more importantly, to buildings that simply work better. A home that has been analyzed and upgraded from a whole-house standpoint is more durable, healthy, comfortable and energy efficient.