Having a house completely covered with tatami mats is unusual. This used to be incredibly popular because it is easy to keep clean and easy to clean when it gets dirty. However, today, a single room covered with tatami mats would be considered cool and okay to do. The reason that tatami is not used to cover the entire house is because we have better materials for a flooring today. It’s not all that uncommon to see wood or tile flooring in most Japanese homes nowadays.
Tatami mats were simply mats made of rice straw and soft rush. However, the cores today have become more durable. Soft rush is still used to create the surface that people would sit and stand on.