Any building requires a certain general amount of internal infrastructure to function, which includes such elements like heating / cooling, power and telecommunications, water and wastewater etc. Especially in commercial buildings (such as offices or factories), these can be extremely intricate systems taking up large amounts of space (sometimes located in separate areas or double floors / false ceilings) and constitute a big part of the regular maintenance required. Systems for transport of people within buildings:   Systems for transport of people between interconnected buildings:   Buildings may be damaged during the construction of the building or during maintenance. There are several other reasons behind building damage like accidents such as storms, explosions, subsidence caused by mining, water withdrawal or poor foundations and landslides. Buildings also may suffer from fire damage and flooding in special circumstances. They may also become dilapidated through lack of proper maintenance or alteration work improperly carried out.