I have a theory that I really hope works. I suspect it won’t though. The ancient Celtic house type - called a crannog - had no real need for a chimney. The way they built and thatched their rooves meant that they stayed dry but the smoke collected high up at the highest point of the roof directly over the fire. Then it just dispersed out through the thatch. As long as there was heat rising the smoke didn’t collect at ground level.
The thatch roof in Valheim does seem to allow smoke to escape through it, so I think there’s a chance I could get it to work. I need to figure out how to build a conical roof with supports though.
*there’s a brilliant reconstruction of one about an hour away from here. It’s actually a sizable building and the roof is really bloody high.