The igloo, a temporary shelter traditionally built by the Inuit, is one of the most recognizable structures in the world. Constructed entirely from blocks of snow, the dome shape is not aesthetic but a practical necessity driven by physics and construction efficiency. This geometry addresses the limitations of snow as a building material while providing protection from the cold.
Structural Stability and Compression
The dome shape is primarily dictated by the mechanical properties of snow. Compressed snow is weak when subjected to tension (pulling apart) or shear (sliding), but it is remarkably strong under compression (squeezing together).
The dome’s geometry acts as a three-dimensional arch, redirecting nearly all external forces—such as the weight of the blocks and wind pressure—downward and outward. This redirection converts the forces into compression, which the snow blocks handle well. The structure is often designed as a catenoid, which is the curve of an inverted hanging chain. This specific curve helps eliminate ring tension, preventing the lower parts of the dome from bulging and failing.
Optimizing Internal Temperature
The dome shape offers significant thermodynamic advantages, making the interior habitable even when outside temperatures are far below freezing. This form encloses the largest possible volume of space with the smallest amount of exposed surface area. Minimizing the surface area reduces the total area through which heat can escape, significantly minimizing heat loss.
The smooth, curved interior facilitates a natural convection current. Warm air generated by occupants rises and collects near the top of the dome, providing warmth. Conversely, colder, denser air sinks to the floor.
A crucial design element is the sunken entrance tunnel and the raised sleeping platform, which create a cold trap. The lowest area of the igloo serves as a sump where the coldest air collects, keeping it separate from the main living and sleeping areas. This setup helps maintain a temperature difference of up to 70 degrees Fahrenheit between the interior and the outside air.
The Spiral Building Technique
The dome’s construction method is intrinsically linked to its final form, allowing a single builder to quickly erect a stable shelter without external support. Traditional construction uses a continuous, upward-sloping spiral of blocks, rather than stacked concentric rings. This technique is self-supporting from the moment the first block is set.
The snow blocks are cut so their outer face is slightly wider than their inner face, and they are tilted inward toward the center. This inward lean allows the structure to support itself progressively as it rises. The builder continues the spiral, decreasing the diameter until only a single hole remains at the top. This final opening is then closed with a precisely cut key block, locking the entire compressed structure into place.