In Hanoi's Old Quarter many of the old style Tube or Tunnel Houses were one room wide and up to 164' long. The narrowest house is only 5.5' wide! Taxes were based on the amount of frontage, so this style saved money for the shopkeepers. Each house has a courtyard in the middle for ventilation. In the past the houses could only be 2 stories high because no building was allowed to be taller than the King's palace.