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While the Inuit word "igloo" can represent many kinds of habitations in a snowy environment this article describes what most people imagine when they think of an igloo: a dome-shaped structure built from blocks of snow (also referred to as a snowhouse). When properly constructed, the temperature inside an igloo will remain between −7 °C (19 °F) and 16 °C (61 °F) with just body heat, even if the temperature outside dips to −45 °C (−49.0 °F)! Building a real igloo is energetic work, however - not something for the faint-hearted. So grab some friends, energy bars and drinks, and get to work!
Make block molds. When making an igloo, it is best to use even sized blocks. Nail together four old boards into a rectangular box shape without a top or bottom, or find rectangular containers, like garbage cans. You'll need at least two different sizes of these. The first one should be about 12" long, 6" high and 4" or 5" wide, and the second one should be a bit smaller, say 10" x 5" x 3" or 4". However, a wall made of 6" blocks throughout will hold up a snow house perfectly, if its top is no more than 6 or 7 feet above the ground.
Clear a flat space in the snow on the ground and mark out a circle shape, trying to keep it as perfectly round as possible.
If there are only a few inches of snow on the ground, make your own snow field. Start at the periphery of the yard and blow snow from the outside to the inside. At the end, you will have a roughly 15 x 15 ft area of snow that is about 3 feet deep (this is starting from 2-4 inches deep). Let this sit overnight but a few hours should do. This process packs the snow to make very strong but also heavy bricks. When you start the igloo, do it up on top of the 3 foot layer so you can dig down for the entrance to make a cold sink.
Make snow blocks. Place the larger four-sided mold onto a flat board and tightly pack snow into it, forcing or ramming in as much as you can.
Sprinkle a little water on the snow, if it is too dry, to make it easier to pack it together tightly.
Hold the mold a little way up in the air, once it is completely packed, and tap the top or sides of it sharply to release the snow block. As one person makes the snow blocks, another can start building the igloo.
Form a row of the large blocks around your circle. Make the joints smooth and even, as there is no mortar for binding the blocks together. If necessary, force loose snow in to fill up the cracks and crevices as the igloo is built.
Form a second layer of the large blocks on top of the first, laying each block above of the joint of the ones underneath, thus staggering the blocks.
Stack additional layers on top, each time moving the bricks in slightly so that the walls will dome inward.
The first course of the snow blocks should be thicker than the others, and the thickness of the walls gradually decreases toward the top. As mentioned earlier, however, size variation may not be necessary, depending on the height of the igloo.
The building is best continued with one person inside the structure and one on the outside to ensure an even inward slant, gradually making a dome.
Cut a cap brick that is close in size, but definitely larger than the hole on top of your igloo.
Two people should lift the brick up and set it on top of the igloo.
One person should get inside the igloo and trim the cap as needed until it fits snugly into the hole.
Fill in the cracks and holes with snow and pack it in as tightly as possible. Smooth out the inner dome walls as much as possible and carve longitudinal grooves inside to allow the melting snow to flow outside without dripping on you.
Dig down to make an entrance to the igloo. If you build it on a gentle slope, then the entrance hole can ramp up slightly into the cave. This will allow the cool air to 'fall out' through the entrance and the warmer air to stay inside.
Build additional rooms if you want them. Simply stack them onto the previous room.
Strengthen the structure.
Drip water over the top of the igloo at night before going to sleep. This will allow the water to freeze and will make the walls stronger.
Poke a small hole near the top, and then light a candle inside the igloo and let it burn. The heat from the candle will partially melt the inside of the igloo, and then it will refreeze into ice, making your igloo stronger.
Be picky about your snow. It must be packable. Also, if there was a frost just before the snow and the bottom layer is slushy, it won't be comfortable to sit inside the igloo.
Get a waterproof picnnic rug so you can be more comfortable.
Snow is heavy. Be careful and make sure not to try this alone in case the igloo collapses.
Never build a fire inside, unless it is very small, as it is very dangerous due to smoke inhalation and rapidly melting snow. Body heat and adequate clothing will keep you nice and warm inside without a fire. A candle is safer to use.
Small cooking stoves are fine if the igloo is large and well-ventilated, but use it sparingly for heating water, not for warmth. Also, try placing the stove above head level so that the fumes vent out directly and you won't breathe them in.
Be careful about the air's oxygen content as most igloos provide poor ventilation.