Snow as shelter: basics and limits

Snow consists of ice crystals with a great deal of air between them. This trapped air makes it a fairly good insulator. The looser and fresher the snow, the more air it contains; wet, heavy snow insulates less well and makes everything wet.

The biggest gain from a snow shelter is wind protection. Outside, the wind constantly carries heat away from the body. Inside, the air is still. Together with body heat and the insulating snow wall, the temperature inside often stays near freezing even when it is much colder outside.

Because the walls are tight, fresh air does not get in by itself. It has to be supplied deliberately through an opening. A ventilation hole in the roof that is kept clear regularly is therefore not an extra but a must.

Before you start digging, check the alternatives: turning back, a hut, a vehicle or an emergency bivouac in the lee. A snow shelter is only worthwhile if you have a shovel, practice, enough time and energy, and dry clothing.

In practice, snow shelters often fail not because of the structure but because people become exhausted and soaked while building. Without a shovel, a snow shelter is barely realistic. In wet snow and thaw conditions it is unsuitable, because the roof weakens and everything gets wet.

The simplest form is usually the best: a body-length trench covered with a tarp, sheet or snow blocks. It is quicker to build and less prone to collapse than a dug cave. A snow cave in a deep drift insulates better but needs a lot of time, experience and deep enough snow – it belongs in supervised practice.

Avalanche terrain is expressly not covered by this text. Never build on or below slopes, under cornices (overhanging edges of snow) or in gullies. Anyone travelling in steep snowy terrain needs avalanche training and the current avalanche forecast.

Snow roofs can collapse and bury people. Never dig into a snow cave alone, always take the shovel inside with you and mark the entrance and roof clearly on the outside so nobody steps on it and the shelter can be found. Let someone know where you are.

Stoves, candles and burners in a snow shelter can produce lethal amounts of carbon monoxide and use up oxygen. The ventilation hole stays clear, the entrance is never sealed completely, and stoves are run outdoors as a rule. Digging also makes you wet and sweaty: take off insulating layers beforehand, work slowly and call the local emergency number (112 in the EU) at signs of hypothermia.

Staying dry is half the battle when building with snow. Take off insulating layers such as fleece or a down jacket before digging and stow them dry. The waterproof outer layer stays on. Work steadily and rather slowly so you sweat as little as possible. After building, put the dry layers back on.

Choose only flat or very gently sloping terrain with no slopes, cornices or gullies above, with sufficiently deep, firm snow – away from paths, ski runs and tracks where vehicles or piste groomers might be moving.

Inside, you never lie directly on snow but on a sleeping pad, backpack or other insulation. Take the shovel and equipment inside with you so you can dig yourself out in an emergency.

Snow shelters are described in military survival manuals – always with explicit emphasis on ventilation and the danger of carbon monoxide. People in cold regions have used snow as a building material for a long time; but that knowledge rests on a great deal of experience and practice.

This text deliberately gives no measurements for wall or roof thickness and no building instructions for snow caves or igloos. Such details depend heavily on the type of snow and conditions and belong in a practical course.

If you are interested in snow shelters, a guided winter course is the best way in. There you learn in safe terrain how different types of snow feel and how strenuous digging really is.