Qashgai in Iran. Notable in each case is the significant impact of the availability of materials and the availability of pack animals or other forms of transport on the ultimate form of the shelters. All the shelters are adapted to suit the local climate. The Mongolian gers (yurts), for example, are versatile enough to be cool in hot continental summers and warm in the sub-zero temperatures of Mongolian winters, and include a close-able ventilation hole at the centre and a chimney for a stove. A ger is typically not often relocated, and is therefore sturdy and secure, including wooden front door and several layers of coverings. A traditional Berber tent, by contrast, might be relocated daily, and is much lighter and quicker to erect and dismantle – and because of the climate it is used in, does not need to provide the same degree of protection from the elements. Permanent dwellings The type of structure and materials used for a dwelling vary depending on how permanent it is. Frequently moved nomadic structures will be lightweight and simple, more permanent ones will be less so. When people settle somewhere permanently, the architecture of their dwellings will change to reflect that. Materials used will become heavier, more solid and more durable. They may also become more complicated and more expensive, as the capital and labour required to construct them is a one-time cost. Permanent dwellings often offer a greater degree of protection and shelter from the elements. In some cases however, where dwellings are subjected to severe weather conditions such as frequent flooding or high winds, buildings may be deliberately "designed" to fail and be replaced, rather than requiring the uneconomical or even impossible structures needed to withstand them. The collapse of a relatively flimsy, lightweight structure is also less likely to cause serious injury than a heavy structure. Over time, dwellings' architecture may come to reflect a very specific geographical locale. Environment, construction elements and materials The local environment and the construction materials it can provide, govern many aspects of vernacular architecture. Areas rich in trees will develop a wooden vernacular, while areas without much wood may use mud or stone. In early California redwood water towers supporting redwood tanks and enclosed by redwood siding (tankhouses) were part of a self-contained wind-powered domestic water system. In the Far East it is common to use bamboo, as it is both plentiful and