Construction accounts for a small fraction of GDP. The chief construction company, the Building Society of Mauritania, is hampered by inadequate manpower and capitalization. To encourage housing development, the government introduced new regulations in 1975 to encourage builders and to compel civil servants to purchase their own property and thus relieve the demand for public housing. The phenomenal growth of Nouakchott and the effects of rural migration, impelled by drought, have strained housing resources. In 1998, over 25% of residents in Nouakchott lived in substandard housing, such as tents, huts, or shacks, as did about 35% of Kiffa residents and 44% of Aioun residents.