27A, Holywell Hill

27A Holywell Hill is a conservatory and seed hall built around 1930, with plans submitted by Percival C. Blow for Ryder and Sons, seed and bulb merchants. The structure is made of rendered brick, reinforced concrete, and a steel frame, featuring a patent glazed roof with semi-circular gable ends and a small central dome over the crosswing. The hall is rectangular in plan, with the main entrance located at the west end, directly accessible from Holywell Hill, and wings at the rear flanking a yard.

The building exhibits classical details and Art Deco-style glazing, standing at one storey high. The symmetrical west front has three sections, with the outer windows set in canted bays supported by pilastered piers. The metal frame windows have patterned glazing bars, and there is a moulded cornice and blocking course. The central doorway features panelled and glazed double doors with an overlight, flanked by windows with margin panes. Above, the glazed semi-circular gable end of the roof includes five tall lights with glazing bars. The cornice continues around the north and south returns, which also have three bays with similar metal frame windows and pilasters, topped by a semi-circular glazed gable end over the central three bays.

The central cupola above the crosswing has a rendered drum and a shallow ogee copper-clad dome with a small ball finial. Originally, there were features over the corners where the roof is now flat. Inside, reinforced concrete ribs spring from square piers to form a ring over the crosswing, which rises above the roof as the drum of the cupola. The intermediate ribs of the vaults, purlins, and glazing bars are made of rolled steel, and a suspended ceiling has been inserted at the springing level.

This building was constructed for Samuel Ryder, the seed merchant, whose office at No 27 is located immediately to the north. It was designed to display the firm's merchandise. Ryder served as Mayor of St Albans in 1905 and was a deacon of Trinity. He is also known for presenting the Ryder Cup, the trophy for the Great Britain versus U.S. golf tournament, in 1927.