The north side of the building covers an area of 82' x 152'. The high-bay area, twice as high as the north area, contains a small mezzanine that supports ventilation equipment. The high-bay area was a radiological control area, where the use of personal protective equipment was required. Building 865 is built on a concrete slab on-grade. The roof is precast concrete with polyurethane foam insulation and neoprene topping.
Interior walls are precast concrete, concrete block, or gypsum board.
The mezzanine has a structural steel frame. Windows present in the bay are industrial multi-paned with metal sashes. Buildings 867 and 868 are exhaust plenums for Building 865. Building 865, built in 1970, was part of the Plant research and development program. The building housed metalworking equipment for the study of non-plutonium metals and the development of alloys and prototype hardware.