The Building Performance Institute (BPI) is the nation's leading building science accreditation organization. The "house as a system" philosophy - which looks at a building's various components (building envelope, attic, basement, combustion equipment, ventilation sources) and the interrelationship between 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, healthier, more comfortable, and more energy efficient. For more information about BPI's standards, take a look at their Technical Standards for Building Analysts (PDF).