But they still built earth homes. I see some other threads along the no-liner option but I didn't see any specifically mentioning Viking stuff. If I'm repeating things, throw me out!
http://www.hurstwic.org/history/articles/daily_living/text/Turf_Houses.htm
This group generally deals with Viking culture but they have this great article on why the old Viking style earth homes were more suited to Northern climates than many modern earth homes.
Particularly interesting is how they dealt with keeping the earth off the structural beams.
These guys use cut sod more than they are using loose earth. I think this is the biggest difference from the typical wofati train of thought. So it's not suitable for all locations (I have woodland lot, so I'm still searching for my linerless plans) but there're loads of people living in grasslands.
And here are some other potent pictures from the article that might help wofati thoughts.
This last photo has me thinking of some ways to increase the drainage around wofati buildings.