An extendable electrical box comprises an electrical box having two open ends to an internal box space having a first depth. The electrical box comprises a mounting structure attached to at least one wall of the electrical box. The mounting structure is configured to mount the electrical box to a vertical wall structure such that the open end faces substantially parallel to the vertical wall structure. At least two extendable first rings each continuously surround one of the two open ends of the electrical box. The at least two extendable first rings are each slidably coupled with the electrical box via the sliding mechanical cooperation of one or more guides with one or more tracks, such that sliding either of the at least two extendable first rings in relation to the open ends of the electrical box expands the electrical box from the first depth to a larger second depth.