An igloo is a housing structure made from snow and sometimes ice. Traditionally, igloos were built by Inuit communities in the arctic, above the tree line where wood is no longer a common resource. Developed for reasons similar to those which led to sod housing, knowing how to build an igloo is valuable when the only usable building material is the snow you stand upon.
While the term igloo derives from an Inuit term that refers to any constructed home, today it is associated exclusively with a dome-shaped structure made from blocks of snow. Snow works as an excellent insulator and ultimately the purpose of the structure is to protect inhabitants from the elements outside. When constructed properly, an igloo can maintain indoor temperatures as high as 20 degrees Celsius with temperatures outside in excess of -40 degrees (Celsius or Fahrenheit, at this point).
Architecturally, igloos are unique in that they are dome structures constructed by raising independent blocks which lean on each other to distribute weight and stress. Creating a pile of snow and digging out a shelter is considered a different kind of structure; a quinzhee. A quinzhee’s structural integrity relies on different architectural principles and as a result they are not considered igloos.
Mathematically, there are optimal ratios between height and diameter which allow the structure of an igloo to eliminate structural tension, but snow also compresses and melts over time, which means any calculations must take these phenomena into account.
Generally if you plan your igloo out properly, you will see good results.
Constructing an igloo starts with finding the right snow. Your primary building material must have enough structural integrity to hold together as a block when cut out of the ground, and to bare the weight of stacked under pressure. Snow is ice crystals and air; that’s it. Under different circumstances, snow can be compacted in various ways which can lock the ice crystals together and make snow stick to other snow. Snow that has been compacted on the surface by the wind is the best and easiest material to use for igloo construction; it retains a lot of air which is good for insulation and it’s relatively light for the amount of structural tension it can sustain. If the snow available is more of a packing snow, it can be formed or molded into blocks. While this will be heavier and denser than air-blown compressed snow, it’s strength makes it the next best thing. Ice is in fact a poor insulator since it usually contains very little air within. It can be handy in building a window for light, but if you can choose between ice and snow as a primary building material; choose snow every time.
Block molds can be made from anything that will retain a bunch of snow and form it; you can use boxes, buckets or chests, but ultimately you will need to cut and shape the blocks for optimal placement and sizing. You can build an entire igloo with nothing but a knife, but snow saws also exist which make easy work of cutting out snow blocks. Of course, we sell snow saws here.
When you have found the kind of snow you want to use, you should figure out where you want the igloo to sit. Many suggest building an igloo on slanted ground, but if you have no idea what’s under the snow (based on its depth) you may not be able to consider elevation in your planning. A natural ridge or small hill can provide a warm sleeping platform inside the igloo but if not available this can be constructed with ice or snow. Either way, a good rule of thumb is to build your igloo in the space which you are cutting your blocks from. Since you will be digging down anyway to create a living space under the surface of the snow, you will be able to reduce much of this work by continuing the hole left where you cut your blocks from, so plan around that if possible. The size and number of blocks required will depend entirely on the size of the finished structure, so consider how many horizontal layers of blocks you may need in order to provide enough height for a comfortable living space.
Blocks should be staggered in their placement around a circular ring and leaned slightly inward. Making the blocks smaller as you work your way up will help keep things more manageable, until you get to the top with a flat, open circle. At this point you must cut one final block; the cap-hole block which acts as a keystone. Start with a block that is slightly smaller than the hole atop the igloo, and carve it down to fit snugly.
With the cap-hole in place, go over the structure and rub snow into the gaps and crevices between all of the blocks in order to properly insulate and strengthen the igloo. Next you will want to create a hole for the entrance; cut an arch out of the blocks at surface level, and if you dug below the surface inside, you should dig a ramp down to this level. It is recommended to construct a short tunnel protruding from the entrance, and this can be done by stacking more blocks or simply resting two against each other in a wedge. With access to the interior, insulate the blocks from the inside and cut out several small holes to help with ventilation. The igloo will keep you warm from body heat and people breathing, but the same things will also fill it with carbon dioxide (and monoxide), which is harmful, and why ventilation is necessary.
The igloo’s entrance can be covered with planks, sheets or animal hide to function as a door and further insulate the structure’s temperature. While you can make a fire to cook food or boil water in an igloo, keep it small and short and only do so with proper ventilation. Fire should not be used for heat in an igloo as living bodies will provide enough sufficient heat and harmful gas as it is.
Since warm air rises, build a sleeping platform above the ground level of your igloo to ensure comfortable nights. If you insulate the entire floor of your igloo with carpets, rugs or hides; it will raise the attainable temperature of your shelter considerably.
While igloos can be constructed entirely by a single person, more people can make the work exponentially easier and quicker. Even having a second person can allow one to construct the dome from the inside while the other from the outside. Refrain from putting weight or stress on the surface of the igloo, especially during construction. Once the cap-hole has been placed and the structure’s snow has had time to settle; a properly constructed igloo will support the weight of a person standing on it, but if you don’t need to stand on it, don’t.