Velvet Mill, Lister Mills, Bradford
Dominating the Bradford skyline is a group of magnificent Grade II* listed Victorian buildings, Lister Mills, with massive stone walls and an iconic 250 foot high chimney, inspired by St Mark’s Campanile in Venice. They were built by Samuel Lister in 1873 and were once the largest silk mills in the world, employing 11,000 people and supplying velvet for stately homes and, in wartime, silk for parachutes. Lister made use of the latest technology at the time; the floors were constructed using Dennett’s patented arched concrete system and supported by cast iron beams and columns.
Today the mills have a new use and the skyline has a dramatic new profile which demonstrates contemporary timber technology – a series of silver-clad apartments, their forms created by timber into curves reminiscent of a skein of spun yarn, reflecting the original purpose of the Victorian building below.
Lister Mills closed in 1992 and slowly slipped into dereliction. In 2000 Urban Splash, in conjunction with Bradford City Council and Yorkshire Forward, started work to bring the former industrial structures back to life, transforming the site into a mix of new homes, offices, retail, leisure and community spaces.
Velvet Mill is the second phase in the development, designed by David Morley Architects. The six-storey mill has been converted into 190 apartments including the row of new rooftop apartments, with 6,500 sq ft of community and commercial space at ground floor level. The stonework has been cleaned and repaired, and new windows have been inserted which respect the original design philosophy by minimising the intrusion of metal frames. Inside, the original cast iron columns, internal brickwork and brick-lined vaulted ceilings have been retained and the tall windows flood the interiors with daylight. A grand staircase, set in a stone tower extending from the main façade, has been restored and acts as the main circulation core, together with a new set of lifts.
Visible for miles around, the dominant component of the Velvet Mill restoration is the rooftop apartments, a series of silver curvilinear shapes. The construction of these dramatic silver-clad forms was entirely dependent on timber technology, using digital fabrication and CNC cutting to create complex curved panels from oriented strand board (OSB) and plywood.
The rooftop apartments
The apartments run the full 108 metre length of the roof, divided at mid-point by the sloping glass roof of the access staircase. Reflecting the repetitive curves of the skein of yarn, they take the form of ten silver-clad curved enclosures, with upper and lower levels which house one- or two-bedroom apartments in a variety of configurations, accessed by central corridors at the lower level. Each curved enclosure is set on the diagonal and stepped back from its neighbours. The stepped forms create double-height areas of glazing which give magnificent views of the centre of Bradford and, in the other direction, of the Yorkshire moors. At each end of the roof a larger curved enclosure houses two-bedroom apartments at ground and first floor, both with generous semi-circular terraces.
From the outset it was clear to the architect and the structural engineer for the rooftop apartments, Price & Myers, that although the apartments defined the concept and style of the whole project, they had to be built to a tight budget. Unlike other parts of the country, Bradford does not have high land values and the budget had to reflect the sale value of the apartments while providing the developers with the margins needed for successful regeneration. Not only that, in practical terms the rooftop was a challenging shape, only 19 metres wide and at a height which was not easy to access for construction.
For Price & Myers, the key to solving these problems was the choice of timber as a structure for the curved enclosures. Timber had all the qualities required; low in cost, light in weight and the ideal material to be prefabricated into curved elements to create cassettes. Assembled from simple timber beams and ribs, the cassettes would fit together in a practical way and be light and small enough to be transported to the site and craned up onto the roof.
As Tim Lucas, partner at Price & Myers, explains: ‘We took inspiration from the Buckminster Fuller quote, ‘In architecture form is a noun, in industry form is a verb’. This reflects much of the structural design motivation of the penthouses – to make the structure create the form and to use the least amount of material in doing it’.
Each cassette consists of a set of eight digitally fabricated curved plywood I-beams comprising curved webs and curved pairs of 25mm thick plywood flanges, glued and screwed together. To brace the I-beams, space them apart and act as a frame to set them out to the correct curvature, they are slotted into sets of OSB noggins set 900mm apart. An outer skin of OSB sheet then provides bracing to the whole panel.
The cassettes were economical to fabricate as the I-beam components – the top and bottom pairs of flanges, the web, the end stiffeners and noggins – all nested neatly onto standard size plywood and OSB sheets, with very little wastage from the sheets that the parts were cut from. The components were designed to be assembled without the need for temporary moulds or jigs; both the I-beams and their longitudinal noggins slot together to align the parts correctly, while the flanges are spliced across the joints to maintain continuity of the structure.
Each cassette is 350mm deep and designed to span six metres across each of the curved enclosures. The edges of the cassettes are fixed to a curved two-storey steel frame which also supports the intermediate floor beams. When complete the structure was insulated and lined with a second timber layer and a standing seam zinc roof covering.
As an additional economy, the structure was designed to a geometry that could be repeated across the rooftop. This simplified construction for the builder and limited the number of fabrication drawings required. The size and weight of the cassettes proved to be ideal for craning up and assembling on the rooftop.
The new roof structure to the mill
The apartments rest on a new roof structure, a concrete slab with trimmer beams which transfer the apartment loads onto.a series of steel universal beams. The beams slot into the original stone piers, into notches which previously housed the bearing ends of the original cast iron roof trusses. As well as providing a base for the new apartment construction, the new roof slab allowed the mill refurbishment and conversion below to take place in a sheltered environment.
RIBA Yorkshire Awards 2019 shortlist
Wood Awards 2019 – Private Sector shortlist
Yorkshire Residential Property Awards 2019 – Best Design Project
Structural Awards 2019 – Commendation for structural artistry
Northern Design Awards 2019 – Best Residential Development
Prepared by the publishing team with contributor Susan Dawson.
November 2018Building Type:
Urban SplashStructural Engineer:
Urban Splash BuildTimber Supplier & Cassette Fabricator:
Commercial Systems International LimitedTimber Elements:
Roof, floor and wall structureTimber Species:
FSC-certified European spruce oriented strand board (OSB) and plywood
Costs and supply concerns rise as recovery broadens in Q1.
This excerpt is taken from the recently published book, Timber Rising: Global Perspectives on Mass Timber Advances for the Tall Building Industry, produced by the Council on Tall Buildings and Urban Habitat in conjunction with the US Department of Agriculture Forest Service.
This article is part of a new...
This document contains a worked example of a 12-storey residential structure made of cross-laminated timber (CL).
It is designed to Ultimate Limit State and Serviceability Limit States in accordance with Eurocode 5 (BS EN 1995-1-1:2004 and the UK
For an explanation of the design principles see...