Recently (January 2005) I was curious about how comfortable an igloo might be. So I located some books that claimed to describe how one is made. The authors must never have actually tried to build one, because some of their information was very wrong!
An igloo can have walls that are 6" or 8" thick. That is fine! But the books I had found showed the first row/layer of blocks being essentially vertical, and that is wrong. They neglected the fact that when the center blocks are installed, they act like the blocks and keystone of a brick arch, they push out sideways really hard! Around 800 years ago, a lot of giant Cathedrals being built in Europe collapsed when the roof was placed on top, because, in the same way it made the walls buckle outward. (For Cathedrals, they eventually solved that with an architectural concept called Flying Buttresses!)
In any case, the bottom row of igloo blocks can NOT sit flat on the ground/snow. They must be slanted inward. So the snow underneath must be packed down at a slanted angle. I recommend around 15°. to 20°.
The outward force due to the weight of the middle top is then applied to that slanted surface, and it does not act to kink the walls outward.
I decided to make a "brick mold" so all my blocks were the same size. This works great for the first two or three layers.
Here is what I made:
I started with four 2x4s 26" long. I used a table saw to
cut one side of them to a curve of 36" radius. So these pieces
were the full 3.5" wide in the center but only around 1.5"
wide at the ends (with one edge still straight. I laid these down
as ribs (which were OUTSIDE the box where the snow would be thrown),
with the flat side down. Then a piece of 1/4"
plywood 12" wide by 21" long was nailed down on top of the
curved edges. This formed a surface that is bowed up in the
middle. (This would actually eventually be the inside surface
of the block.)
Next, two pieces of 1x12 about 28" long will become the sides. The top edge of these were marked and table saw cut to a radius of 44" radius. (This radius was because I decided to make an igloo that was around 7 feet in diameter.) They were nailed into the side ribs, such that the top edge curve is 8" above the curved floor, but only with two big nails right now! Those sides will be spread out at the top (which will be the outside of the igloo) so that each higher block is tilted a little more inward.
I got two short pieces of 2x12", around 15" long for the end pieces. Both ends are cut at a slight angle so that one edge (the top) will be the 15" while the other (the bottom) will be 12". So a triangular piece 1.5" in maximum width is cut off each end. These pieces have to be pushed down between the sides to spread them out, all the way down to the bottom. Now, these end pieces will NOT be nailed straight across! They will be nailed at the farthest extreme of the floor (to one side piece), but they will be tilted in 1.5" before being nailed to the other side. Both ends are angled in like that to make the top of a block 3" narrower than the bottom.
This is a rather complex shape! The curve of the floor of the mold will be the inside wall of the igloo, and they are nice and smooth. The blocks start out at the ground 15° or 20° and the top of each block is tilted inward a little more (due to the form sides being flared out. Each block has a top that is 3" smaller than the bottom, because as the walls slant in the total circumference of a layer gets less.
It is a great idea to line the entire inside of the form with black polyethylene (like a tarp) or Tyvek or some other plastic sheeting, so the blocks come out easier.
Making blocks is really easy! Using a shovel, pitch loose snow into the form. Then step on it to pack it down, and even jump up and down on it! Pitch more snow in and pack it again. I found that three fills usually was enough snow for a full block that was really packed and solid. You can use a straightedge to smooth out the top, but I usually just left my footprints visible on the outside of the igloo! The filling and packing takes about 3 minutes per block. Once the form is filled, it is just rolled over and slightly shaken. The block MAY slide out! You can't shake too violently or drop it without possibly breaking the block in the process. When blocks did not fall out (which was common since I did not use the plastic liner), I found that a standard hand saw could loosen the block from all four sides and the block always then dropped out. Then just start laying them down for the first layer, and then the second.
By the time you get up to the third row, a new problem occurs. The top of the second row is so slanted that the third row blocks will want to slide inward! Until you get the entire row around, where they can press against each other sideways, temporary supports are needed for each of the blocks. These don't have to be very strong, but there have to be around ten of them. Once the entire layer is in place, the supports can be removed, and the blocks will slightly press together.
Each row above does the same. Above the third row, I found it desirable to make a different "brick mold", much narrower, but still 8" thick and 12" in height. The curvature of the bottom of the mold needs to be of tighter radius, although the smaller blocks makes the radius less important.
The very top piece gives you a choice. It could be left out completely, remaining a 12" diameter open space as a chimney for a fire. It could be a cork-shaped piece to close it up completely. Or it could be a cork-shaped piece that has a rather small hole through the middle.
As long as none of your blocks disintegrate, the igloo will be complete and very solid. I am pretty sure you could climb on top although I did not test that. Keep in mind that if ANY block disintegrates that row would all immediately collapse in, along with all the layers above it! So it pays to really stomp down on the smow in the form!
I found that when the temperature was extremely cold (below 10°F) the snow did not pack very well, and some blocks were questionable. When the temperature was around 20 to 25°F, the snow seemed to pack extremely well, and the blocks were all impressively strong.
I placed a piece of 1" thick blue styrofoam insulation on the floor and my sleeping bag on that. It was surprisingly warm and cozy, even without any fire or heater. I closed the top piece completely, so I couldn't use a fire, but I used a campstove, and very quickly it got up to around 80°F inside, so warm that I started sweating! I turned the heater way down, and it was great!
The heat inside is a good thing. It causes the inside surface to briefly melt and freeze back into a thin layer of ice, which made the igloo even more airtight! A little melting occurred (because I like it pretty warm!) but the water ran down the walls and never bothered me. The walls and ceiling did not seem materially thinner after a night of sleeping bag camping inside it. But I guess it would eventually weaken the walls and roof if it was kept really warm inside.
I was surprised that the light of my camping lantern did NOT make the whole igloo glow from the outside. Only where the seams between the blocks was any light visible from outside. Even tents get lit up by a lantern, but I guess that 8" of packed snow blocked the light.
One person could use such a form and make an entire igloo in one day. I worked more leisurely and took parts of three days. If several people work together, just a few hours should be necessary.
I stayed in it overnight, and used a campstove and a camp lantern. I wasn't sure how much heat I would need, and was amazed that the two burner propane campstove very quickly got it so warm that I was sweating! Pretty weird to be laying on top of a sleeping bag, sweating in underwear, in an igloo! So I turned off one burner and greatly turned down the other, and kept it at a nice 72°F or so all night. As cozy as being inside the house!
However, I do not see how Eskimos deal with the very cold ground. If I didn't have my slab of insulation on the ground (like along one side), the ground was so cold that it was very penetrating. Actual igloos are built on very deep snow in extremely cold temperatures. Seems like it would be extremely uncomfortable!
In Chicago area weather, there were mostly days in the 20s and lower 30s, with around 15°F each night. So I was surprised that much of it collapsed after about a week. I realized that the structure was essentially like a brick archway. If even one brick would crumble, the entire arch would immediately collapse, because they are all squeezed together.
It might have been that one of my blocks had some flaw in it, which allowed it to collapse. Weeks later, most of the blocks still survived, with some of the walls still standing. Clearly, extreme attention is needed to make sure that not even one of the blocks could crumble!
But it makes me wonder just how long a real igloo lasts in Alaska or northern Canada. Does the heat they have from their fires inside gradually make it disappear? Do they have to build a new igloo each year? Interesting questions that had not occurred to me before my adventure!
( http://mb-soft.com/public/index.html )
C Johnson