This TECHnote discusses the requirements for microbial control in buildings and how these are addressed in NATSPEC. Microbial control aims to minimise health risks. These include Legionnaires’ disease, Pontiac fever, Hypersensitivity pneumonitis and Humidifier fever, posed by viruses, fungi and bacteria. Control may be achieved through proper design, installation, commissioning and maintenance of cooling towers, warm and hot water services and air handling systems.