Thursday03 September 2015

Restoring the Derby Roundhouse

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Maber Architects has retained many original features in its refurbishment of Derby College’s Roundhouse and other railway buildings

Derby College Roundhouse Campus
Maber Architects
Structural engineer

BWB Consulting

Pride Park, Derby

Walking around Derby’s Roundhouse, the oldest surviving building of its kind in the world, it’s easy to become a bit of an anorak.

Maber Architects’ sympathetic restoration of the grade II* listed building, where locomotives were repaired in the early days of steam, has retained most of the remaining original features. The 16 rail spurs for the engines can still be crossed over and the 12m-diameter turntable is still operational with minor modifications.

A clear laminated glass floor over one of the ash pits allows views into the basement where the engines were once cleaned, and soaring European redwood trusses criss-cross the majestic 40m-diameter roof, which was engineered by Robert Stephenson, son of pioneering railway engineer George Stephenson.

The 16-sided load-bearing masonry structure, forms the centrepiece of a collection of buildings on the eastern part of a 2.8ha site near Derby railway station that was once part of a large railway works operation.

The Roundhouse, together with the adjoining and impressive carriage shop (grade II*), clocktower (grade II), offices and an engine shop — which was subsequently burnt down in 1950 — were built in 1839 for £62,000 by North Midland Railway.

In the western half of the site, the Midland Counties Railway built the two engine sheds (grade II*) in 1844 for a paltry £4,000.

In September 2007, after winning an Ojeu competition in 2005, Maber Architects led the two-year £46 million restoration and new-build project. Its task was to restore all the existing listed buildings and construct two new ones (the Kirtley building and the Stephenson building) to create a vocational skills centre for Derby College.

Maber Architects has refurbished the railway buildings at Derby College.
Credit: Alan Fletcher
Maber Architects has refurbished the railway buildings at Derby College.

The college had already commissioned Maber Architects to carry out a feasibility study on the site in 2003. Had this not made such a convincing case for the location’s viability, the listed historic buildings would eventually have crumbled away.

Maber director Ian Harris says: “The structural reports revealed that the damage to the buildings was accruing at a rate of about £600,000 a year from 2000, mainly due to water ingress and vandalism.

“In 2007, the damage had increased to £1 million annually. At these rates, the buildings would never have lasted and we would have lost the Engine Shop within the year.”

Derby College bought the site for £1 from Derby City Council. The council had left the site to deteriorate for 20 years, allowing pigeons to infest the buildings, cast-iron windows to be ripped out and sold for scrap, and water to seriously damage the timber structure of the roofs.

Harris recalls that soon after the restoration began, he went into one of the buildings and climbed a staircase to look at a room. When he returned the following day, the staircase had collapsed. “It really was falling down around our ears,” he says.

The new Roundhouse Campus has only just opened and students have started moving in, although the official opening day isn’t until October 23.

Harris heaps praise on Derby College and its principal, David Croll. He believes that without their vision and a willingness to put their trust in the practice, the city would not now have this impressive legacy.

“Other projects always foundered because they wanted to carve up the historic buildings,” says Harris.

“Derby College succeeded because, architecturally, it has fitted the accommodation into the existing buildings and it simply wanted a lot of large spaces.

“I hope we’ve now ensured a future for the site and given it a notable character.”

The restored and refurbished Roundhouse, which will be used for social events for up to 2,400 people, has already proved a great success. Its open, light space will no doubt give its much larger namesake in Camden, north London, some healthy competition.

Restoring the roundhouse roof

“It’s a miracle the roof hadn’t fallen down,” says project engineer David Allott of BWB Consulting, referring to the discovery that 10 of the roof’s 16 double inverted primary trusses had failed due to water damage. “Both the gutters and downpipes were compromised due to years of neglect, which had led to water ingress and extensive decay,” he says.

The roof is a timber trussed conical form, supported off an inner cast-iron ring beam and columns and an external masonry wall. The truss system relies on the counterbalancing of the 16 principal trusses, with the pin at the top formed by a circular ring beam.

There are also 32 secondary trusses, two between each primary, which are supported by the cast iron ring beam, external wall and a purlin spanning between principle trusses at the top.

Critical to finding out the species of timber and how much timber repair was required, a micro core survey was carried out by Hutton & Rostron Environmental Investigations. It took a sample from every piece of structural timber for analysis and gradually built up a computer model to work out which parts of the structure worked and which didn’t.

It concluded that there were two principal problems: water ingress, which caused decay, and poor quality of timber — knots as deep as the timbers themselves were revealed.

Wherever possible, timber roof members were strengthened by bolting on steel plates to preserve as much of the original appearance as possible. Any retained timber members were cleaned with a light steam and finished with a Danish wood oil.

Where timber had rotted, a minimum length was cut out and a new timber section of the same European redwood was installed and spliced to the original member via bolted steel plates.

Credit: Alan Fletcher

No attempt was made to conceal the restoration. Maber’s Ian Harris says the concept of “honest repair” was inspired by William Morris, whose valuing of old and new is the restoration’s guiding principle.

In other instances, key structural supports had to be replaced. At least 75% of one major diagonal member in each of the trusses had to be replaced because they were overstressed.

“Those diagonal members were acting in compression and supporting a large portion of the roof load and the cupola,” he says. “In the worst cases, the members were buckling and as a consequence had deflected by as much as 100mm.”

The original cupola was destroyed and a new timber cupola finished with a lead roof was designed based on historical photographs.

A continuous ring of double glazed rooflights was installed, fitted with actuators to control the windows’ opening and closing.

A sarking board restrains the top flange of the trusses, which creates a diaphragm that distributes horizontal loads and ties the whole roof structure together. About 80% of the sarking board was retained; the rest was rotten and had to be replaced.

A vapour control barrier was added, together with an expanded polystyrene insulation slab, counter battens, a breather membrane, more battens and then reclaimed slates.

Original print headline - Derby College Roundhouse Campus

Project team

Architect Maber Architects, Client Derby College, Structural engineer BWB Consulting, Timber survey specialist Hutton & Rostron Environmental Investigations, Main contractor Bowmer & Kirkland, Rooflights The Rooflight Company, Roofing contractor Martin-Brooks, Specialist timber repair Quadriga, Timber restoration Beech Restoration


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