It is constructed by excavating snow so that its entrance tunnel is below the main space in order to retain warm air. Construction is simplified by building on a steep slope and digging slightly upwards and horizontally into the snow. The roof is domed to prevent dripping on the occupants. Adequate snow depth, free of rocks and ice, is needed — generally is sufficient. A quinzhee is similar, but constructed by tunneling into mounded snow rather than by digging into a natural snow formation.