I've lived in a couple of houses built in the mid 1700s with parts even older than that. They were cob cottages, one with a thatched roof, so very thick walls instead of insulation. Plumbing and electrics were just added over the years. Windows were single glazed, so not very efficient. But pretty comfortable nevertheless, provided you remember to duck when going under beams. Houses this old are not unusual where I live in Devon, but most are more recent.

https://en.wikipedia.org/wiki/Cob_(material)