The 300-acre site housed some 2000 patients and was based on the “Echelon plan” – a specific arrangement of wards, offices and services within easy reach of each other by a network of interconnecting corridors. This meant that staff were able to operate around the site without the need to go outside in bad weather. Unlike modern British hospitals, patients in Severalls were separated according to their gender. Villas were constructed around the main hospital building as accommodation blocks between 1910 and 1935. Most of the buildings are in the Queen Anne style, with few architectural embellishments, typical of the Edwardian period.
The hospital closed as a psychiatric hospital in the early 1990’s following the closure of other psychiatric institutions. However, a small section remained open until 20 March 1997 for the treatment of elderly patients suffering from the effects of serious stroke, as a temporary building for the nearby Colchester General Hospital which was in the process of building an entire new building for these patients. Since 1997 the remaining structures have changed little. Architecturally the site remains an excellent example of a specific asylum plan. However, the buildings have suffered greatly from vandalism. In 2005 the main hall was subjected to an arson attack and in 2007 the charred building was demolished for safety reasons. The five boilers were removed from the central boiler house in 2007. In 2008, the sale of the hospital site, including its extensive grounds, collapsed due to the slow-down in the building industry. Planning permission was however granted in 2011 to redevelop the site.