Rapid urbanisation led to fields and allotments disappearing in favour of cheaply built houses, often tightly packed together into the smallest space available. Houses were built on top of inadequate foundations and with substandard materials to reduce costs. Each house was separated by a single brick depth with a small room on each floor; ground-floor rooms served multiple purposes, as the remaining available space was used for bedrooms. By the 1830s, back-to-back houses had gained a reputation nationwide for spreading disease, and major cities including Manchester and Liverpool prohibited their construction in the 1840s and 1860s respectively. The Leeds Improvement Act of 1866 imposed regulations on the building of new houses, which included gated yards, wider streets and improved interior design. The Medical Officer for Health unsuccessfully sought to abolish their construction in about 1880, by which time population density had improved to 200 people living in 50–60 houses per acre.