Command of the Oceans, The Historic Dockyard, Chatham, Kent

Introduction

‘A dock finished for the finest fleet the sun ever beheld, built lately by our gracious sovereign Elizabeth’ is a 1606 description of the naval dockyard in Chatham, on the river Medway. It grew to cover 400 acres, laid out to manoeuvre huge timbers between the river, the mast ponds and the joinery workshops and the dry docks. Thousands of men – shipwrights, blacksmiths, joiners and sail makers – worked here on the Navy’s timber warships, including in 1765 HMS Victory. In the late 19th century Chatham adjusted to the new technology of metal hulls and later constructed submarines, before it finally closed in 1984. The site, now classified as an Ancient Monument of National Importance, with more than 100 buildings, including 47 Scheduled Ancient Monuments, was transferred to a charity, the Chatham Historic Dockyard Trust, which conserves the buildings and opens them to the public.

In 1995 the timbers of a warship were discovered beneath layers of floorboards in the Wheelwrights' Shop, one of the workshops at the Dockyard. This turned out to be the remains of HMS Namur, a ship of the line which fought alongside Nelson at the Battle of Cape St Vincent in 1797. The discovery became the catalyst for ‘Command of the Oceans’, a grant-funded project to preserve the ship’s historic timbers and re-interpret the history of the dockyard, improve the experience of visitors and reinvigorate existing exhibition spaces.

The project, designed by Baynes and Mitchell Architects, has reconfigured the historic landscape, creating new, clearly marked pedestrian routes to help visitors find their way through the complex set of buildings and yards. At the heart of the scheme is a new link building and gallery, slotted into a narrow space between a range of listed Georgian naval workshops – the Wheelwrights' Shop and the Mast House and Mould Loft. Like these buildings, the new building is gable-fronted, but is distinguished from them by its sharply pitched roof and seamed black-patinated zinc façade. Visitors walk up a gently sloping bridge to the main entrance and a new raised ground floor level; this new level extends into the Wheelwrights' Shop, creating a spacious café with kitchen and toilets while allowing just enough headroom below the café floor for a gallery to view the remains of HMS Namur. The gallery is reached by a ramp enclosed in board marked concrete, intersected at half-level by other ramps which lead to new exhibition spaces on the other side of the centre in the Mast House and Mould Loft workshops. 

The use of timber

Although the new link building is only six metres wide and 36 metres long, its structure is remarkably complex, accommodating the conservation of historic monuments, changes of level on plan and between adjoining buildings and the construction of a new floor to span over the historic remains of The Namur. Its primary structure is timber, chosen to complement the massive oak structures of the adjacent historic workshops. A series of 120 x 200mm glulam columns run along both sides of the the new building, alternating with concrete columns which give additional lateral restraint to resist wind loads. To reach the new café in the Wheelwrights' Shop, visitors pass through spaces between the columns, framed with deep 60mm thick CLT portal casings which also provide additional structural bracing to the roof. To reach the galleries they walk down a ramp alongside what was formerly the external wall of the ancient Mast House, boarded in horizontal textured timbers and now visible between the glulam and concrete column spacings.

The columns support 200 x 200mm glulam beams with flitched connections to sets of exposed glulam scissor trusses, a construction appropriate to the very steep (65 degree) roof pitch. As a scissor truss construction does not require horizontal ties it could accommodate the different eaves heights of the two adjoining historic workshops. The roof build-up above the trusses is lined with a 60mm thick cross-laminated timber (CLT) deck which does away with the need for any secondary timber structure.

The structure of the new timber floor

One of the most significant challenges was to build a new floor in the Wheelwrights' Shop, directly above the Namur’s historic timbers, while protecting them from damage. Tension cables were run through the building, picked up at either end by rows of large concrete blocks, and supported at intervals along their length by chains connected to box trusses spanning between the original beams. Metal trays sat on the cables, providing a working platform above the ancient timbers (in effect, a suspension bridge) that allowed the new floor to be built. Once it was complete, the temporary floor was removed.

James Stevenson, Partner, Price & Myers, explains his work on the floor structure:

‘One of the key details in the design of the undercroft was the exposed connection between the new floor over the historic timbers and the bowed timber posts of the Wheelwrights' Shop.

A steel collar detail was developed that sat nearly entirely within the depth of the new floor to avoid any impact on sightlines in the undercroft below. Two L-shaped fabricated steel brackets were offered up on either side of the posts and clamped together with M20 bolts through the posts.

The load to be transferred from the floor to the posts was considerable and so steel shear-plate connectors – discs with a projecting rim that was cut into the timber to improve the connection’s shear capacity – were welded to the back of the brackets and cut into the posts. The posts were regularised first over the height of the brackets to achieve a tight fit between the posts and the brackets, so that the connectors fully engaged with the timber.

The variation in the position of the posts was accommodated in the detailing of the connection between the collars and the floor beams.

It was decided to fabricate a mock-up of the collar-to-post connection. This tested regularising the post, using a jig to drill straight holes through the 300mm timber post, and then fitting the collars with their shear-plate connectors. This process gave the contractor confidence in the design, and the design team the confidence that the contractor could achieve it!’

The lower ground floor gallery

In the lower ground floor gallery the architect has created a space which offers an intimate relationship between the viewer and the archaeology, the remains of HMS Namur. As project architect Brendan Higgins explains: ‘The gallery is unheated, naturally ventilated and un-separated from the timbers. Viewers can smell the earth on which these relics sit and feel the cool air which surrounds them. We achieved this by removing all but the primary structure from the entire western elevation of the Wheelwrights' Shop below a specified datum line. We excavated to create a new, lower level and underpinned the existing structure with a new concrete slab, while re-supporting the existing thick timber columns on new granite padstones’. 

Sustainability

The glulam structure and CLT, supplied by Egoin Timber Construction, are of whitewood spruce sourced from Germany and constructed in their factory in Spain. All the timber used was certified PEFC and FSC, with formaldehyde-free glues used to bond the timber. Any offcuts created in the manufacture of the structural elements were reused as biomass in a boiler to heat the factory. The glulam and CLT elements were prefabricated and cut to size before being delivered to site; as a result the amount of waste created onsite was minimal, simply a few recyclable sheets of plastic and small cardboard boxes (containing screws). The structure is made of 63m3 of timber, which equates to 62 tonnes of sequestered CO2.

The glulam and CLT elements were finished with Osmo PolyX-Oil White finish and a clear flame retardant treatment. 

Awards

RIBA Stirling Prize shortlist 2017
RIBA South East Building of the year 2017
RIBA South East Conservation Award 2017
RIBA South East Award 2017
RICS South East Project of the Year 2018
RICS South East Tourism and Leisure, Winner 2018
RICS South East Building Conservation, Highly Commended 2018
Wood Awards, Highly Commended, Commercial and Leisure category 2017
Civic Trust Award 2017
Kent Design and Development
Conservation Award 2017

Completion Date:

May 2016

Building Type:

Link/entrance building and gallery

Location:

Chatham, Kent

Client:

Chatham Historic Dockyard Trust

Architect:

Baynes and Mitchell Architects

Structural Engineer:

Price & Myers

Main Contractor:

Fairhurst
Ward Abbots Ltd (initial)
WW Martin Ltd (completion)

Project Manager:

Artelia UK

Joinery Company:

Egoin

Timber Supplier:

Egoin

Timber Elements:

structure, interior walls and roof deck, interior fittings

Timber Species:

whitewood spruce, Douglas fir

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