An igloo is a structure built from blocks of compressed snow which are carefully shaved and placed to fit in optimal positions. Igloos are closely associated with Inuit culture, although many Native North American peoples built igloos, some of which were quite large and elaborate. Examples of igloos can still be seen in the far reaches of North America today, and people in snowy regions sometimes enjoy building models of these interesting structures in the winter. An igloo may also be referred to as a snowhouse.
A classical igloo is dome-shaped, with the blocks of ice being built up in a spiral. The roof has a small hole for ventilation, and the entrance is dug into the snow so that it is lower than the igloo itself. This creates a cold trap, ensuring that the ambient temperature inside the igloo stays relatively warm. In fact, some igloos get quite temperate inside, thanks to body heat and the use of heated stones to raise the interior temperature.
The construction process involved in making an igloo is rather remarkable. The blocks are cut from snow which has been heavily compacted, ensuring that they will be strong, and the structure is built without the use of mortar or supports. Once the igloo is finished, the people inside actually contribute to its strength and stability, because heat causes the inside blocks to start melting, while the cold refreezes the melted water, creating a smooth sheet of ice which further insulates the igloo.
A basic igloo stays warmer than the outside because snow is an excellent insulator, and some Native North Americans also added skins and furs to the lining of their igloos to make them especially warm. When seated on the raised sleeping platform in the back of the igloo, people would have been able to take advantage of one of the warmest spots in the structure. Even with the airhole for ventilation, an igloo can get pretty stuffy inside, but considering the ambient temperatures outside, most people think that the stuffiness is worth it.
Some igloos are built as temporary structures for the use of hunters and travelers, and they tend to be smaller and less elaborate than permanent igloos. A permanent igloo is much larger, designed to accommodate a crowd and to connect with other igloos, including temporary structures built for festivals and special events. Often, several families or groups shared the same igloo, with some permanent igloos having divided rooms to facilitate sharing of the space.