Architecture in the metropolitan centers is essentially French. Many African people, especially the Mossi, live in round huts with conical straw roofs or in rectangular huts with flat roofs. There is a housing shortage in the urban centers due to rapid growth. In Ouagadougou, most houses are built with mud brick and/or plaster. About 10% are made with cement block. In 1991, there were about 1,399,149 households. About 92% of rural dewllings and 65% of urban housing were owner occupied. In 1999, only 53% of all homes had access to improved water systems and only about 24% had access to improved sanitation systems. There is an average of 6.9 people per household.