Tree houses, treehouses, or tree forts, are platforms or buildings constructed around, next to or among the trunk or branches of one or more mature trees while above ground level. Tree houses can be used for recreation, work space, habitation, observation or as temporary retreats.
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In some parts of the tropics, houses are either fastened to trees or elevated on stilts to keep the living quarters above the ground to protect occupants and stored food from scavenging animals. The Korowai, a Papuan tribe in the southeast of Irian Jaya, live in tree houses, some nearly 40 metres (130 ft) high, as protection against a tribe of neighbouring head-hunters, the Citak.[1]
Tree houses are an option for building eco-friendly houses in remote forest areas, because they do not require a clearing of a certain area of forest. The wildlife, climate and illumination on ground level in areas of dense close-canopy forest is not well suited for human habitation.
Tree houses can be built with a wide range of materials. Wood is commonly used for structural parts and cladding due to its strength, light weight and low cost. Steel is used for brackets, cables and bolts, including specialized tree bolts capable of supporting up to 6,000 pounds (2,700 kg).[2] Builders of tree houses sometimes use recycled materials or parts, such as reclaimed window frames, doors and used lumber. One motivation for this is to promote sustainability by re-using resources. Reclaiming materials can also save money compared with buying new materials and can add a retro or abstract style to the design of the structure. Fabrics can be used to produce non-rigid temporary structures that are more like tree tents than tree houses.
In modern tree house construction, supporting the structure can be summarized by the following methods:
Tree houses supported by stilts do not need the tree to take any of the weight stress of the building materials and potential strain and injury cased by puncture holes.[3] Stilts are typically anchored into the ground with concrete although new designs, such as the “Diamond Pier”, accelerates installation time and protects sensitive root systems.[4] Stilts are the easiest method of supporting larger tree houses, and can increase structural support and safety. Adding stilts to tree houses built with other methods of support is an option to increase stability and safety.
Friction and tension fasteners are the most common method of securing tree houses. These include nails, screws and bolts. Because this method requires punctures in the tree, the fewest possible number of these should be utilized to minimize stress.[5] Nails are generally not recommended to attach a tree house to a tree.[6] A development called the treehouse attachment bolt which can support greater weights than earlier methods, is now commonly used by many tree house companies worldwide.
Tree houses that use this design are among the least cluttered and unique types today. Rope and cable are the most used methods of suspension. Suspended tree houses are among the most difficult to construct and access.[7]
Since the mid-1990s, recreational tree houses have enjoyed a rise in popularity in countries such as the United States and parts of Europe.[8] This has been due to increased disposable income, better technology for builders, research into safe building practices and an increased interest in environmental issues, particularly sustainable living.
Increased popularity has, in turn, given rise to demand for businesses covering all building and design work for clients. There are over 30 businesses in Europe and the USA[9] specializing in the construction of tree houses of various degrees of permanence and sophistication, from children's play structures to fully functioning homes.
Many areas of the world have no specific planning laws for treehouses, so the legal issues can be confusing to both the builder and the local planning departments. Treehouses can be exempt, partially regulated or fully regulated depending on the locale.
In some cases tree houses are given exemption from normal building regulations, as they are not considered to be a building in the normal sense of the word. An exemption may be given to a builder if the treehouse is in a remote or non-urban location. Alternatively, a tree house may be included in the same category as structures such as garden sheds, sometimes called a "temporary structure". There may be restrictions on height, distance from boundary and privacy for nearby properties. There are various grey areas in these laws, as they were not specifically designed for tree-borne structures. A very small number of planning departments have specific regulations for tree houses, which set out clearly what may be built and where.
The tree house has been central to various environmental protest communities around the world, in a technique known as tree sitting. This method may be used in protests against proposed road building or old growth forestry operations. Tree houses are used as a method of defence from which it is difficult and costly to safely evict the protesters and begin work. Julia Butterfly Hill is a particularly well known tree sitter who occupied a Californian Redwood for 738 days, saving the tree and others in the immediate area. Her accommodation consisted of two 3m2 (29 sq ft) platforms 60 m (200 ft) above the ground.[10]
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