How To Build An Igloo: More Wisdom From Weather Eye

We’re celebrating the late and much-missed Brendan McWilliams and Illustrated Weather Eye, our beautiful new collection of his Irish Times column. Back in November 2005 he offered readers a "topical tip": How To Build An Igloo...

Officially, this is still the autumn, but we have begun already to feel ‘the icy fang and churlish chiding of the winter’s wind’. But we are lucky; we have to brave such harsh conditions only now and then. For inhabitants of the far north, however, swirling snow and icy winds are a normal, everyday experience, and they face particular challenges in providing themselves with shelter from these hostile elements.

In the southern parts of their domain, the Inuit peoples can avail of stones and limited quantities of wood to make their huts, but from time to time in winter their hunting activities take them to places where the only available building material is snow. There their survival depends upon the igloo, a masterpiece of structural strength combined with thermally efficient engineering.

Firstly, the heat inside in igloo causes a vapour-proof glaze to form upon the snow-packed walls. Then the powerful insulating capabilities of snow ensure that those inside enjoy a temperature regime that is at least 10 degrees warmer than the air outside, and the living area is entirely draught-proof. Moreover, the igloo’s hemispherical topology presents the smallest possible external surface area for any given volume, so that loss of heat by radiation is as low as possible.

An igloo can be constructed fairly quickly, but it requires skill and experience to get it right. The snow, for example, must be exactly right in density; if it is too soft it crumbles, and if it is too hard, it will break up into sharp, misshapen, quite unmanageable slabs.

Having found the right snow, the igloo builder cuts it into slightly concave blocks, which are then set on edge to form a circle. The top surface of the base is shaved so that successive rows of blocks will form an ascending spiral, narrowing with height. The roof is capped with a keystone, a wedge-shaped block of ice carefully sculpted to be wider at the top than at its base, and then the gaps between the blocks over the whole surface of the igloo are grouted with additional quantities of snow.

At this point the structure is a fragile one, and could crumble easily if treated carelessly. Resilience is provided by lighting a whale-blubber lamp inside the igloo and then closing up the entrance with a block of ice. The snow on the inner surface starts to melt, but because of the igloo’s vaulted shape the water does not drip, but rather soaks gradually into the blocks, wetting them for a considerable proportion of their depth.

The final step is to unblock the entrance and remove the lamp, allowing a surge of cold air to transform the inside of the structure into a dome of solid ice, strong enough to allow a polar bear to crawl across the roof - which one sometimes does - without causing any damage.

25 November 2005