Naval dock buildings, market halls and factories

Another fruitful area for the development of long span roof structures was in the naval dockyards.

Early in the nineteenth century a number of roofs were built over shipbuilding slips in naval dockyards. Many of these timber structures were replaced with iron structures, an event which Coad links to the early use of corrugated iron as a roof covering. Some of these trusses appear to be iron copies of timber originals, but there is also evidence of a move away from truss configurations (like the King Post) which were more suited to timber, to the "W"-shaped framing more appropriate for iron and steel.

At least 16 naval dockyard buildings built between 1844 and 1857 incorporated trussed roof structures of cast iron, wrought iron or a composite construction involving both. It has been relatively recently that these dockyard buildings have begun to be acclaimed as having an important place in the history of the development of iron roof structures; a place hitherto principally reserved for the railway roof structure. Often it was a designer of railway roofs who was also responsible for these dock buildings.

In other building types such as the market hall and the mill there was a gradual move from timber to iron roof structures.

In the all-iron roof trusses cast iron was commonly used for the compression members with wrought iron used for the rafters and tie bars. A number of this kind of market hall roof survive in the UK today including those at Todmorden, Accrington and, "the finest of all, at Preston".

In France Camille Polonceau developed a simple trussed rafter system which was widely used in a variety of building types.

Polonceau’s trusses might be a combination of timber and iron or, more commonly, were made entirely of iron. An early Polonceau truss system was used for the roofs over the Paris-Versailles Railway in 1837. These trusses had timber principals, cast iron struts and wrought iron ties: a form which became very popular in Europe in the 1820s and 30s

In England Charles Fox of Fox Henderson used composite trusses spanning 80 ft. (24.5m) in the design of the roofs for Pembroke Dock in 1844.

This span was greater than any railway roof structure built up to that date (Manchester Victoria Station roof trusses, erected in the same year were, at 59.5 ft., the best of the competition from railway roof structures). The Fox Henderson firm was also responsible for the design of dock buildings at Woolwich and Chatham which were demounted and remounted elsewhere.

Greene’s boat store at Sheerness was a notable development as the first rigid, multi-storey frame.  It is also worth noting that this building uses a lightweight cladding material throughout.

One dock building which has gained deserved attention relatively recently is the boat store at Sheerness (Greene 1858-60). Its importance lies principally in being a very early cast and wrought iron multi-storey framed building braced by portal action (i.e. stiff beam/column connections). However it does also have an iron trussed roof structure. In this case, though, the spans involved are a relatively modest 45 ft. (13.9m) in each of three bays.

In many cases the simple iron truss was found to be adequate and it is interesting to consider the circumstances when alternatives were considered appropriate.

When Fowler came to provide a roof for Hungerford Fish Market in 1868 he chose cast iron in preference to timber to avoid "impurity" and "offensive odour". His simple, elegant structure consisted of a flattish single bay portal frame with cantilevers projecting from the eaves. Like Greene's Sheerness boat store it relied on joint stiffness for lateral stability. The sizing of the structure was based on model tests (a common technique used at the time in bridge design) which Fowler regarded as giving conservative answers.

The design was unusual and for that reason was well publicised; but there appear to have been no imitators. Rather it was the pressure to increase spans in railway structures which led to major innovation and change.