Snow is an excellent insulator. That, combined with its sculptable properties, makes it the perfect source of emergency shelter. If you're in a cold, snow-covered environment and need to make a warm, reliable shelter, it pays to know about building snow shelters. There are a variety of different kinds of shelters, suited for different conditions.
The snow cave is a very simple snow shelter in which you dig a tunnel and cave into the snow. This shelter is designed for use on a hill or slope where there's an amply deep snow drift of somewhat compact snow. One digs a tunnel into the snow and then digs out an interior that's high enough to sit up in. The roof should be arched, and the roof and walls should be one to two feet thick. The living area should be raised up so that you're not subject to drafting from the entrance tunnel. Because this shelter is designed on a snow-covered slope, avalanche needs to be a primary concern and proper testing should be done before building. Ventilation is also important, and you should poke a ventilation hole--especially if you intend to use a stove or other heat source.
The Quinzee shelter is an ideal snow shelter for conditions in which the snow is soft and you don't have a slope. It requires less technique than an igloo and is a good option in a variety of conditions.The concept is quite similar to the snow cave, but since you don't have a slope, it requires you to pile up snow and then dig a tunnel and cave as above. Pile snow about six feet high and 10 feet in diameter, then leave it to harden for several hours. At this point, you can build the shelter by digging in. To save time, pile up your gear or other available material, then shovel the snow mound on top of it so that the inside is largely carved out for you.
The igloo is a shelter that requires hard, solid blocks of snow. It's a good option when there is several feet of solid, hard-packed snow. You'll also need the proper tools for cutting, such as a snow saw or machete. This well-known shelter from the Inuit natives entails cutting blocks from the snow and stacking them into a spiraling dome. The base of the igloo should be about a 10-foot circle. An entrance tunnel is cut out. The tunnel is used so that the floor of the shelter is automatically above the entrance.
This shelter is a fast, emergency shelter that works when you don't have the proper conditions or time for other types of shelters. Dig a rectangular hole into the snow just large enough to fit in and put you fully below ground level. If the snow is hard, cut blocks and use them to create a roof by leaning them at an angle on either side. If not, use a tarp supported by branches or other form of roof. The shelter gets you below wind level and makes use of snow as insulation.