Igloo
An igloo (Inuit languages: , Inuktitut syllabics (plural: )), also known as a snow house or snow hut, is a type of shelter built of snow, typically built when the snow is suitable. Although igloos are often associated with all Inuit, they were traditionally used only by the people of Canada's Central Arctic and the Qaanaaq area of Greenland. Other Inuit tended to use snow to insulate their houses, which were constructed from whalebone and hides. Snow is used because the air pockets trapped in it make it an insulator. On the outside, temperatures may be as low as , but  on the inside, the temperature may range from when warmed by body heat alone. Nomenclature. The Inuit language word (plural ) can be used for a house or home built of any material, and is not restricted exclusively to snowhouses (called specifically , plural ), but includes traditional tents, sod houses, homes constructed of driftwood and modern buildings. Several dialects throughout the Canadian Arctic (Siglitun, Inuinnaqtun, Natsilingmiutut, Kivalliq, North Baffin) use for all buildings, including snowhouses, and it is the term used by the Government of Nunavut. An exception to this is the dialect used in the Igloolik region. is used for other  buildings, while , (plural , Inuktitut syllabics: ) is specifically used for a snowhouse. Outside Inuit culture, however, "igloo" refers exclusively to shelters constructed from blocks of compacted snow, generally in the form of a dome. Types. There are three traditional types of igloos, all of different sizes and used for different purposes. Construction. Snow igloos are not spherical, but are built in a catenary curve, a shape more closely resembling a paraboloid. Using this shape, the stresses of snow as it ages and compresses are less likely to cause it to buckle because in an inverted paraboloid or catenoid the pressures are  nearer to being exclusively compressive. If the walls are of uniform thickness and density, the maximum compressive stress at the base of a paraboloid is formula_1 where formula_2 is the diameter at the base, formula_3 is the height, formula_4 is the unit weight of the snow, and formula_5. Since stress is a force per unit area, if the walls are of uniform thickness the compressive stress is independent of wall thickness; thicker walls provide better insulation but do not strengthen the structure because of added weight. The maximum compressive stress at the base of the igloo can be obtained by  multiplying S,/yd times the snow unit weight y and the mean igloo base diameter. The individual snow bricks start out 4-sided and being cut out of the ground with saws and machete-like blades, but are then often cut into 5 or 6-sided shapes to increase structural interlocking, similar to the stones used in the Inca Empire. Igloos gradually become shorter with time due to the compressive creep of the snow. Building methods. The snow used to build an igloo must have enough structural strength to be cut and stacked appropriately. The best snow to use for this  purpose is snow which has been blown by wind, which can serve to compact and interlock the ice crystals; snow that has settled gently to the ground in still weather is not useful. The hole left in the snow where the blocks are cut is usually used as the lower half of the shelter. Snow's insulating properties enable the inside of the igloo to remain relatively warm. In some cases, a single block of clear freshwater ice is inserted to allow light into the igloo. Igloos used as winter shelters had beds made of loose snow, skins, and caribou  furs. Sometimes, a short tunnel is constructed at the entrance, to reduce wind and heat loss when the door is opened. Animal skins or a snow block can be used as a door. Architecturally, the igloo is unique in that it is a dome that can be raised out of independent blocks leaning on each other and polished to fit without an additional supporting structure during construction. An igloo that is built correctly will support the weight of a person standing on the roof. Traditionally, an igloo might be deliberately consolidated immediately after construction by making a large flame with  a (, stone lamp), briefly making the interior very hot, which causes the walls to melt slightly and settle. Body heat is also adequate, although slower. This melting and refreezing builds up a layer of ice that contributes to the strength of the igloo. The sleeping platform is a raised area. Because warmer air rises and cooler air settles, the entrance area acts as a cold trap whereas the sleeping area will hold whatever heat is generated by a stove, lamp, body heat, or other device. The Central Inuit, especially those around the Davis Strait, lined the living area with skin , which could increase the temperature within from around to .