A discipline that deals with the technological aspects of buildings, including the properties and behavior of building materials and components, foundation design, structural analysis and design, environmental system analysis and design, construction management, and building operation. Environmental systems, which may account for 45–70% of a building's cost, include heating, ventilating and air conditioning, illumination, building power systems, plumbing and piping, storm drainage, building communications, acoustics, vertical and horizontal transportation, fire protection, alternate energy sources, heat recovery, and energy conservation. In addition, to help protect the public from unnecessary risk, architectural engineers must be familiar with the various building codes, plumbing, electrical and mechanical codes, and the Life Safety Code. The latter code is similar to a building code and is designed to require planning and construction techniques in buildings which will minimize possible hazards to the occupants.