What is the strongest sized igloo?

[Chris]

I am going to build a few of these outside of Crested Butte this year for overnight backcountry use. What is the strongest/most durable igloo size? I ask because the curve is different (or appears so - based on the size you are making). The 7 footer is too small since we want to be able to sleep at least two people in the igloo. I think the 11 footer is probably too damn big (takes too long to build). So between the 8, 9 and 10 - what will hold up the longest?

Will build in a protected shady area.

[Igloo Ed]

The strongest igloos are the 8 and 9 foot igloos, the rise and span are basically the same ratio and the 8 inch wall offers enough support for the pressures in the wall.
When going to the 10 or 11 foot the rise/span ratio changes and puts more pressure into the walls causing them to compress more which makes the igloo shorter. If it compresses evenly, the igloo will not buckle/sag but the chances of everything working out perfect is pretty slim.
The snow conditions will make the biggest difference though. Hopefully you can get up and build them early in the season with TG snow. It's tough to learn the packing of TG snow but they are the strongest.
The foundation too, it needs to be packed very deeply.
There's more in the thread about sagging igloos.

Sorry to be late to reply.