The complex was designed in the Romanesque (Norman) style, in gault brick, with considerable ornamentation with red brick arches and dog-tooth string courses. The three entrance doorways were decorated with Norman dog-toothed red brick arches, whilst the main entrance, facing the river (now hidden by an extension) was further decorated with the coats-of-arms of the MBW and adjacent counties. There was originally a magnificent chimney, 207 feet high, which has since been demolished.
The capitals of the many columns and mullions on the outside of the building and the supporting corbels to the arched overhanging main cornice, are of different designs, and although some of these are repeated, no two side-by-side, are alike.
The interior of the Engine House was provided with wrought and cast iron work of the most ornate design. The four engines are placed in the corners of the building, the centre of which is occupied by an octagonal structure of iron columns with richly ornamented capitals, supporting iron arched screens and the open octagonal well on the main beam floor. Handrails were of tubular brass highly polished, and the ironwork was painted in natural colours following those of the leaves, branches and fruit represented.The openwork upper iron floors were painted in french grey and vermilion, whilst the shafts of the main columns were in indian red. The elaborately painted panels in the octagon, immediately below the beam floor, incorporated the monogram of the Metropolitan Board of Works, the same device being included in the centre of the cast-iron screens on the working floor