Due to the original office and test room needing to be vacated for the installation of switch gear for extensions to the ring main supplying the Perth City Council, a decision was made to construct a two-storey independent building on the Summers Street side of the power station. It measured 17m x 9m and is often referred to as the Administration Building.

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Constructed in 1941 by A. N. Hill for a contract sum of £3,585, it housed the offices on the top floor, with a workshop, store room and meter testing room on the ground. 

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Despite the power station closed in December 1985, the Administration Building continued to be used for SECWA's laboratory requirements.