Use these physics tips on how to build igloos, and you can become the most popular person during the new ice age!
Perhaps an asteroid hit the earth and kicked up enough dust to block out the sun. Perhaps global warming caused extreme temperatures at the lower end of the scale in your neck of the woods. Perhaps a supervillain with a Persian cat got ahold of a machine that controls the weather. Whatever happened, it resulted in you wandering through a frozen wasteland without shelter. You need a place to stay the night, and io9 can help you build one. The first step is to avoid some common misconceptions about igloos.
Igloos aren't often made of ice. In fact, ice can be a pretty poor construction material. It's heavy, difficult to sculpt, and isn't any good for insulation. The best material to build your shelter out of is blocks of snow. Although snow and ice are made up the same stuff, frozen water, its structure is different. Ice is a rigid crystalline structure which transmits, and steals, heat rapidily. Snow is made up of small ice crystals interspersed with pockets of air, and air is a very good insulator. These air pockets can maintain a difference of 40 degrees between the inside and the outside of an igloo, and do it without sucking body heat away as dramatically as ice does.
Igloos also aren't the half-spheres that they're often shown as. A semi-circle is a very bad structure to build, engineering-wise. The principles that hold an igloo up follow the same ones that hold up an arch. The top and the sides have to be balanced against each other in order for the structure to stand. If the sides are sloping inwards, it's easy for them to prop the roof up. Although a half-circle looks like it has inward-sloping sides, when those sides hit the earth they are exactly perpendicular to it - standing straight up. This puts a lot of stress at the bottom of the structure, since that section of the wall is being pushed outward by the snow above it.