Numbers 4 5 and 6 Slip Covers and Machine Shop Number 6

Numbers 4, 5 and 6 Slip Covers and Machine Shop Number 6 are a group of slip covers dating from 1845-47, built by Messrs George Baker and Sons within Chatham Dockyard. They are constructed from a cast and wrought iron frame with corrugated iron sides and roof.

The structure has a rectangular plan, incorporating aisles and connecting to form a single cover over three slips. The building is of one storey, arranged as a 10-bay range with three wide gables. The frame is exposed, revealing four stages, with an open ground floor beneath a continuous glazed stage. The upper stages feature 6-light and 4-light sash windows, with corrugated sheet gables, sides, and roof, and folding doors. A three-bay section to the left connects to Slip Cover No.3 and includes iron posts supporting a corrugated iron upper floor with three metal-framed windows.

The interior features composite iron frames consisting of I-section cast-iron columns with vestigial Tuscan capitals. A wide semi-circular arch spans across the slips, with principal rafters extending over the aisles and segmental arches over the aisles, supported by diagonal braces and light trussed purlins. Various attachments for line shafting remain, along with supports for a gantry crane by G BUTCHARD/GRAVESEND.

These slip covers were introduced from around 1814 to protect ships undergoing construction from the weather. The Baker roofs distinguished themselves from earlier designs by reducing reliance on the cantilever effect and increasing the distance between frames to 9.5 meters, connecting them with light trussed purlins. They represent an exceptionally early example of a complete iron frame, marking a significant development in constructional history. Earlier iron roofs, now demolished, had followed designs similar to those of Seppings' wooden roofs. Brackets for travellers were added in 1863.

The buildings form a notable group with the 1837 timber slip cover to the south and the larger 1855 slip cover to the north, as well as the other iron covers within the steam dockyard, all illustrating the evolution of free-standing engineering frames.