It’s my understanding that when my ancestors were drunk, they were a pretty fun lot.
Short, though. I was AMAZED to see the door of a stave church and hear that it was actually person-height.
Scroll down here to see the average height of men in Scandinavia in the Middle Ages: http://www.vikinganswerlady.com/vikheight.shtml
I've spent a lot of time in Scandinavia and seen a lot of the old buildings. Yes, people seem to have been shorter back then, but maybe not by more than a couple inches on average. Also, people in general were shorter in previous centuries--or I should say, we're taller now, probably due to advances in nutrition in the West over the last century or so.
I spent four months in Korea back in 1988, and at 6'3" I was literally the tallest person in the country I saw during that time. But now there are a number of Korean young men who are that tall. The health and diet of the country has improved and made a difference.
BTW, one other reason for low doorways and ceilings in old buildings in northern climes could be in order to heat the house and keep the heat in.