Equipment: Snow shovel, carpenter's rip saw, aluminum snow saws.
Site preparation : Choose a site with deep, compressed snow but no avalanche potential. Stomp down the area with snowshoes or skis, then with boots. Let the snow set up for 30 minutes while you take a break or eat lunch. If the snow is very dry and fluffy (usually not a problem in the Pacific Northwest), you may need to shovel down to a firmer layer in order to cut good blocks.
Dome construction : Mark out a circle for the igloo base. This circle is your guide for the first block layer. Don't make it too big. It's easier to enlarge the inside by digging down and out than stacking blocks to make too large a dome.
Use the shovel to dig a square pit about two feet deep, just large enough so you can use the saw to cut the bottom of the blocks. Remove the first four blocks or so. Cut them about six to eight inches wide, and as long and deep as the length of the saw (about 20 inches). Place the blocks along your circle, leaning in at about a 15-degree angle off vertical. Trim the edges of the blocks as needed to fit tightly against one another. Repeat until you have a full circle. Use the snow saw to trim the top of several adjacent blocks so that they angle toward the ground. This ramp allows you to build successive spiraling layers upward.
As much as possible, place each block so it overlaps two blocks below it like bricks on a house. Increase the angle inward as you add each layer (i.e., the first layer is 15 degrees off vertical, the second 30 degrees, the third 45 degrees, and the last is almost 90 degrees). Be sure you have good contact on the two sides that touch already-laid blocks. Chink and caulk the gaps carefully to stabilize the structure you can't build a solid structure on an unstable foundation. It's important to have a second (or third) person patching the holes and gaps from the outside of the igloo, as well as handing in blocks dug from the entryway.
If you plan to sleep in the igloo (as opposed to sleeping in a tent that is attached to the igloo), then you must decide where the entry and sleeping platform will be, usually opposite each other. The door should be crosswind or on the leeward side of the igloo to minimize the accumulation of drifting snow. You need to cut down one layer for the entire interior, and another layer or two where the entry and kitchen areas will be. The entry area gives you a place to stand and also serves as a cold air well, making the sleeping area relatively warmer. Remember when you're cutting out blocks along the inner wall to continue the 15-degree angle outward. This increases the interior about one foot in width for every two feet you dig down.
A good-size igloo (about seven feet across at ground level) will hold a sleeping platform with room for three adults. Don't dig down so deep that you can't reach the ceiling while you're building the dome. It is best to put the final, keystone block into place while standing inside the igloo. Pick a block that is slightly larger than the hole in the roof that you need to fill. Turn the block on end and lift it through this space. Turn the block flat, then gently lower it into the hole, trimming its sides at an angle so it wedges in like a plug. This keystone block should exert equal pressure everywhere that it touches.
Details mentioned in this article were accurate at the time of publication