Even just the specific knowledge of building a house is probably a generation removed from most people these days. It scares me to think of just how fragile we really are.
Sure, but what is forgotten makes room for novel ideas which are hopefully sometimes improvements. Plus, now we have computers to write and share this knowledge so it doesn't always have to be memorized.
Technically, there are more Latin speakers alive today than cumulatively during the Roman Empire. However, I think negligibly few are _native_ speakers.