Igloos R Us

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With winter and snow now upon us, there is a chance some of us may be able to escape to Whakapapa or Mt Hutt. If you are taking the family, here is a project to keep them busy, appropriate resource and building consents notwithstanding.

It may help if you are a card-carrying Licensed Building Practitioner. You never know who you may meet on the snowy slopes these days.
Inuits built their igloos of any suitable material, but to the outside world the term is generally taken to mean a shelter built of snow. There were three traditional types: small, medium and large. Large could have up to five rooms and house 20 or so people. Beginning igloo builders are advised to think small.

As with all structures, you need the right materials. The snow must be well compacted to possess enough structural strength. But it must also be sufficiently yielding to be able to be worked easily. Wind-blown snow whose ice-crystals have become interlocked is the bees knees.

Put on gloves, and cut and trim a number of blocks using a long thin knife. The video (see YouTube reference at bottom of opposite page) shows the best size.
The hole the blocks come from should now be opened up to provide the lower half of the igloo. Decide on the entrance location — away from the prevailing wind is probably best — and dig a short channel into the snow from this point. This will be the entrance passage and will keep the heat in and the wind out.

Architecturally, an igloo is unique. Its dome is raised out of independent blocks leaning on each other and cut to fit in place, without using additional supports during construction.
Stack the blocks in a circle around the hollow in a spiral, in which each block becomes progressively taller. As each is stacked on earlier ones it needs to be pushed down firmly. The pressure causes the snow to melt where the blocks touch. The moisture refreezes and welds the blocks together.

As successive layers build up, fill any residual holes with snow pushed in hard. This provides both mortar and a draught excluder. Continue until the dome is complete. Smooth the exterior with additional snow pushed firmly onto the surface.

An igloo built correctly will support the weight of a person standing on its roof. And in the traditional igloo, heat from the oil lamp causes the interior to melt slightly. The melting and refreezing builds up a layer of ice on the inner side of the dome that contributes to the strength of the igloo.
The sophisticated builder may wish to provide a window. This can be done using a single block of ice inserted in place of one of the snow blocks — after construction is completed. Ice blocks are not easy to come by adjacent to a ski field, and this is perhaps best left for igloos built on the flats, as in Central Otago.

Similarly, igloo builders need to think ahead as to door flaps. A deer or goat skin is ideal. Beds can be made of raised packed snow covered in sheep skins. The higher the beds the more they are warmed by the hot air trapped under the dome roof.

Snow is an excellent insulator. Like expanded polystyrene it comes with built-in air pockets. As a consequence, igloos are surprisingly warm and comfortable. However, heating comes entirely from body heat, and the inside temperature typically ranges from -7°C to a balmy 16°C.

Before you start it might pay to watch a segment of the 1922 documentary Nanook of the North. It shows an experienced Inuit igloo builder at work, demonstrating the use of an ivory knife to cut and trim snow blocks, the stacking of the blocks and how to make and install a window.

It is available on YouTube: www.youtube.com/watch?v=oEEOK6e1nLE&feature=related.