Iron frames in textile mills

Historic textile mills, now redundant, introduced the metal skeleton frame to world architecture. Their new uses can be facilitated by subtraction as well as addition.

Verdant Works, Dundee, shown as the internal scaffolding came down in 2015, following significant investment by the Heritage Lottery Fund and Historic Scotland. The rotten floor boards were removed and not replaced, leaving their impression in the beams. Galleries permit the iron-and-timber frame to be appreciated, and the light to flood into new interpretive displays by Dundee Heritage Trust. (Photo: Jim Burns, Dundee Heritage Trust).

The iron frame of the mill is the precursor to the steel frame of the skyscraper. In the industrial revolution the need for fireproof systems was recognised after several costly fires in early timber-floored mills. Iron frames could provide the support required for solid floors. Some of these pioneering structures were almost immediately demolished.

One of the most important, Ditherington Flax Mill, Shrewsbury, survives and is now in the care of Historic England. Built in 1797, it has the first iron beams, and as both its floors and walls are brick, the shell of the building is incombustible. The power system that brought rotative power to the spinning frames was threaded through the ironwork, vertically through small holes cast into the beams and soon afterwards horizontally on two floors. Spans of 20 feet or more require intermediate supports. Square timber posts continued to be used in warehouse construction for much of the 19th century, with timber pads wedged above and below the posts to spread loads and avoid crushing.

Cast-iron columns offered much greater compressive strength and slenderness. The oldest industrial building yet found to contain them in a regular layout is Bell Mill at Stanley Mills, Perthshire, of 1786, conserved and presented by Historic Scotland. Its cruciform columns transfer load through each wooden beam. The primary concern was to transmit mechanical power. Structural needs were secondary.

Next was the development of interconnecting columns which transferred loads through floors. Columns could spigot through beams where they met or the ‘saddle’ transferred load down either side of the beam to the next column. This seems first to have been adopted in textile mills, and is almost universal in mid- to late-19th century floor maltings.

Timber beams could be tensioned by wrought-iron rods running either side of the beam to meet at cast-iron stirrups. This – the composite or trussed beam – is apparent on a building exterior as a regular series of cast-iron tie plates, often wrongly seen by surveyors as evidence of attempts to remedy building defects.

Timber continued to be the most common flooring in industrial buildings throughout the 19th century, fire-resistance perhaps being enhanced by lath and plaster or by fitting beads to joins between ceiling boards. Alternatively laminated timbers produced floorboards 2-4 inches thick that would char rather than burn: the ‘slow-burning’ floor favoured by American insurers that enforced a virtual exclusion of structural iron from US textile mills. This heightens the peculiar importance in early iron-framed construction of British textile mills, and particularly flax spinning mills.

Two rows of cast-iron columns were not an optimum layout for the spinning mule used in the cotton and woollen sectors, so the majority of English and Scottish early 19th-century cotton mills had timber floors. Of all the Scottish woollen mills in the four main tweed and tartan producing counties, only one wing is fireproof – Ettrick Mill, Selkirk, 1850, with floor arches of whinstone, not brick. The number in the English woollen industry (Huddersfield and Stroud areas) is also low compared to the higher proportion of worsted mills (in Bradford, Keighley, Halifax) that are fireproof.

The ideal beam form was debated after some dramatic failures, including cumulative collapses in Oldham and Salford. The parabolic hog-back was introduced to overcome the stresses in the centre. Usually its bulge will be hidden within the depth of the floor but there will often be locations where part of the floor has been removed and the cross-section may be examined. If carrying a water tank, or flat flagstone floors, the hog-back is inverted, becoming instead a ‘fish belly’.

The oldest beams had an inverted T-section, and a very narrow bottom flange. A cambered underside was adopted in the design-and-build package supplied by Fenton, Murray and Wood of Leeds to Broadford Works, Aberdeen, in 1808, and seen in their mills in Leeds, Shrewsbury, Whitehaven and Whitby. Iron-framed buildings of the 1820s and 1830s favoured a flat-bottom flange of around six inches, the better to serve as springing points for brick arches. Experiments in Manchester by Tredgold (1822) and Hodgkinson (1830) led to a small upper flange, giving an I-section parabolic beam. Around 1838 William Fairbairn applied that new beam form to at least three mills in Northern England, the two survivors being Shaddon Mill, Carlisle, and Hunslet Mill, Leeds. Most engineers and iron-founders were content to adopt the I-section over parallel-sided rather than parabolic bottom flanges. They were doing so by 1850.

Nine fireproof flax mills in Dundee and nearby Brechin, built in the boom of 1828-1837, exhibit different combinations of details that suggest the form was still evolving. Columns are relatively narrow, with entasis (narrowing towards top and bottom for a pleasing visual effect, discovered by the ancient Greeks) because they are usually cast solid. Beams are pre-Hodgkinson, inverted T with no top flanges. Connections between them are formed by shrink rings, on the principle that metal contracts as it cools, binding the frame together. Five of these are converted to housing, in a reversible way so that structural details may be examined in future. Three are buildings at risk. What is locally common might be seen as nationally and internationally very rare.

All iron beams of the first half of the 19th century repay study, to track the pace of these ideas across the country. Opportunity might arise during demolition for archaeological investigation and recording– some have even been tested to destruction by UMIST – or when carefully taking out one bay of a brick arch, such as where a new stair might go. This was done for example at Mid Mill in Stanley Mills, recorded and published by Historic Scotland.

Surviving roofs include various combinations of timber (at least as sarking or battens to fix slates), cast and wrought iron. Inspiration for some came from railway train sheds, with fully tensioned, wrought-iron roofs. Others introduced compression elements such as the Polonceau truss, named after the French engineer. These trusses have decorative as well as functional cast-iron struts between wrought-iron triangulated principal rafters and tension members.

An attic form developed peculiar to Dundee’s jute and flax mills. Most were built with cast-iron frames supported on twin rows of columns in a three-bay, nave-and- aisle arrangement. This led on to the development of gothic traceried roofs that have a very dramatic and surprising aesthetic impact in 11 surviving mills in that city, one in Kirkcaldy and another five documented before demolition. There are at least six different patterns, gothic or more simply detailed, the first erected in 1851 and the last in 1885.

As Baxter’s own foundry built five of that firm’s own mills, those patterns match and were used also at Verdant Works, while each of the others is unique. Natural light from above helped the reeler to see flaws in the yarn. Large spans were not required at floors below because the spinning frames were heavy but static, unlike the mules used for cotton and wool, moving to and fro on tracks facing one another. Cotton and woollen mills therefore adopted roofs of multiple pitches and valleys (such as Listers’ Mill, Bradford, to which new pods have been added by Urban Splash), until eventually roofs became so wide in Lancashire that the opportunity was taken to place concrete water reservoirs on top of them.

In Dundee 20 textile mills have been converted to housing, 13 of which contain internal iron-framed structures while the remainder have new interiors (one of them as a result of a fire and six because they were not listed). West Bridge in Kirkcaldy almost had the indignity of a facade retention inflicted on it, but it too retains its internal structure after some persuasion by Historic Scotland. Near-misses like this, and even insurance problems, led to the commissioning by Historic Scotland of a practitioners’ guide by Tom Swailes. [1]

How can this uniquely Dundee aspect of material culture best be appreciated? A residential use has suited the proportions of many of them, although one bay of Pullar’s Dye Works in Perth is now fixed to a multi-storey car park. Upper Dens Mill, Dundee, has a common area containing artworks, a large chess set and four bays visible of the roof to be enjoyed by residents of Hillcrest Housing Association. West Bridge Mill, a foyer in Kirkcaldy, has some iron trusses exposed in its training suite. More elaborate sections of iron work are now to be enjoyed within the flats of other mills (South Mills, Tay, Taybank and Camperdown Works) due to the need to maximise the value, space and quality of light inside apartments. So twin-level or mezzanine flats might now have flower baskets or other decoration hanging from the tracery, according to the whim of the resident.

At Camperdown Works, largest of the jute mills, there are communal areas in which the iron tracery may be enjoyed together with the massive fluted doric columns of a beam engine. A long stretch of the south wall opens out at first floor through a colonnade of big cast-iron columns, rather like Liverpool’s Albert Dock, leading on to a series of shed roofs also framed in cast iron. Several of these were damaged while being stripped out for scrap by a previous owner, but the rest are gathered to form a pergola that makes an extraordinary vista for residents and visitors. Slates and timber were already lost, so the decision not to restore a now-missing roof covering was relatively easy.

The most recent, and long-overdue, intervention in a Dundee textile mill is the refurbishment of the High Mill at Verdant Works. Since 1995 interpretation of the textile industry has been delivered by Dundee Heritage in warehouse sheds and an office arranged around the mill yard, while conversion of the main part of the spinning mill awaited a future phase. During that time of benign neglect, feasibility work by Tayside Building Preservation Trust considered alternative uses. These included possible display of the journalistic output of DC Thomson, development as student apartments, or use as an archive along with the adjacent former printing works. Here the arched, cast-iron roof is over timber floors, which succumbed to rot. It became apparent that substantial upgrading of floor loading would be necessary in any of these outcomes.

Instead the solution is brilliantly simple: take away the floorboards and do not replace them, or not yet anyway. The frame is now visible from different angles as light floods the building from above. The reduced floor space is flexible, and headroom is no problem for large items, like a Boulton and Watt engine of 1802.

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