The available room involving the internal and exterior shells of a dome or cupola of masonry.
The available area between the internal and outer shells of a dome or cupola of masonry.
In a masonry cupola, the area involving the inner and external shell; by extension, the space involving the inner masonry cupola and also the external dome-like roofing of wood or metal, such as St. Paul's Cathedral, London. Also called intercupola.
How would you define interdome?