>>6223635/5
Here is the relevant text from the following page, which I didn't scan because it has no more shelter info:
"...As with a snow cave, the igloo's entrance ceiling should be at least 6 inches (15 centimeters) below the level of the floor (fig. 3-14f). Place ventilation holes at 45-degree angles in at least two spots in the igloo roof (fig. 3-14f)."
