West Pavilion, Southern and Western Ranges, Barrack Block and Staff Quaters to Former Ordnance Survey Office Buildings.

The West Pavilion, Southern and Western Ranges, Barrack Block and Staff Quarters are part of the former Ordnance Survey Office Buildings located on London Road. This site was the original location for the Ordnance Survey, which moved here from the Tower of London in 1841. The buildings were originally constructed as barracks around 1800 and were later converted into an asylum for military orphans in 1816.

The Barrack Block is an early 19th-century, one-storey structure made of yellow brick, featuring a round-headed carriage entrance with keystones. Attached to this is the Western Range, which dates from 1867, also built of yellow brick and consisting of two storeys. It has a parapet with a dentil cornice that conceals the roof, and it includes sash windows, some of which are triple. The doorcases are simple in design.

There are two detached pavilions, both two storeys and made of yellow brick. The West Pavilion has a hipped slate roof, while the Southern Range features a cornice and three sash windows, each with stuccoed fan moulding above. The doorcases on these pavilions are also simple. To the south lies the former Staff Quarters, dated 1868, which is a two-storey yellow brick building with eight sash windows, a modillion cornice, and a band between the floors.