Indoor toilets were at first a luxury of the rich and only gradually spread to the lower classes . As late as the 1890s , building regulations in London did not require working - class housing to have indoor toilets ; into the early 20th century , some English homes were built with an upstairs toilet for use by the owners and an outhouse for use by the servants . In some cases , there was a transitional stage where toilets were built into the house but accessible only from the outside . After World War I , all new housing in London and its suburbs had indoor toilets .

Question: when did indoor toilets become common in america
Answer: After World War I