Loch Lomond, Scotland, Balloch

Introduction

The new building is the headquarters of the Loch Lomond and Trossachs National Park Authority, which covers an area of over 700 square miles to the north and west of Balloch. The new building provides flexible workspace for over 120 staff including associated community groups, staff from Scottish Natural Heritage and SEPA. The design team has striven to meet client demands for an affordable, sustainable building that not only sets new standards for office design but one that also affects ways of working, allowing staff to undertake a planned process of change. It is anticipated that the building will help the National Park to adopt new ways of working; the space will primarily function as an administrative centre that becomes an information point and meeting focus for staff and the community at a central hub in the park.

The design concept was influenced by the constraints of the site, an unprepossessing location on the edge of a roundabout. The architect took advantage of this position to create a sinuous, curved structure that follows the contours to form a double-roofed, two-storey building. A large proportion - more than 35 percent - of the National Park is forest, and the park authorities were anxious that this was reflected in the use of timber in the building. The structure is one of the largest greenwood timber frames ever built in the UK. It contains offices, meeting and conference facilities, a cafe, library and public meeting spaces.

 

Building description

Reflecting its rural environs, the building takes the form of a twin-pitched barn which extrudes itself along a shallow S-shaped curve. Walls and roof are clad with slate – the park area is dotted with slate quarries – while the rear gable is clad with larch strips. The main entrance to the headquarters is at one end, where three bays of one of the paired gables create an imposing double-height oak-framed porch. Inside, at reception, the ground floor is defined by a series of courtyard spaces, described by the architect as ‘urban squares’, which include a double-height cafe area and library. The twin pitch of the structure reflects the internal spatial arrangement on the first floor; two 8m wide office floor plates – the classic dimension for ventilated one-sided office spaces – are divided by a central 4m-wide ‘street’ with a glazed rooflight above, set at the junction between the twin pitched roofs. The street follows the sinuous curve of the building and allows the space to naturally divide itself into cellular office spaces without the need for divisions; the rooflight lights and ventilates the interior.

 

Use of timber

The structure, at 78 x 20m, is the largest greenwood timber frame constructed in the UK. Its design was a collaboration between the architect Page/Park, structural engineer Buro Happold, Timber Engineering Connections and structural engineer Hannah Reed, plus the fabricators, Carpenter Oak and Woodland who in turn employed SKM Anthony Hunt to design the frame connections.

The building’s cross-section, 20m wide, is made up of two 8m-wide frame structures separated by the 4m-wide central ‘street’. There are 26 post-and-beam frames in the 78m long building; their vertical elements consist of massive 6.2m-high Douglas fir columns, each 300 x 650mm. SKM Anthony Hunt developed steel flitch plates to connect the Douglas fir elements; they are set within slots in the timber, protecting them from fire.

Externally the rear wall and end gables are clad with vertically fixed Scotlarch, Russwood’s trademarked Scottish-sourced European larch cladding.

 

The design of the structure

Timber was chosen as the only sustainable material available for use as a structural space frame for a building. The Douglas fir frame is a cutting-edge timber structure combining post and beam construction with pre-fabricated wall panels and floor ribs and a site-built skin. Because of the large open plan spaces this minimal structure was required to transfer the wind loadings through a very few highly-engineered floor and wall panels to the massive Douglas Fir buttresses along the edge of the building.

Post and beam structures readily withstand dead loading i.e. the weight of the structure itself plus the weight of the occupants and the building’s activities, but they require stiffening to resist the sideways loadings, such as the force of wind. Diagonal brace members (timbers, metal rods or cables) are the approach normally adopted in traditional post and beam design, however this approach was inappropriate given the architectural concept of this particular building. Initial assumptions that a conventional studded wall system would provide the required stiffness in every situation became challenged as the complex loading calculation developed.

In most areas, timber stud and ply panels with some assisting metalwork met the engineering requirements, but in some of the stability walls the loadings were too great. Gordon Cowley of Timber Engineering Connections and Hannah Reed, in consultation with the building team, developed a solution, unique to the UK, of using pre-fabricated wall panels with a central vertical ply sheet acting as the web, with timber top and bottom flanges (essentially a very tall I beam) with vertical ribs at regular intervals to resist buckling of the web.

The upper floor played an important structural role. The original concept was to use a method of construction used for bridge building in the US called parallel laminated construction, using timber from the National Park, but the practicalities of the system, primarily the performance in fire, unfortunately had to rule out this exciting concept. The intermediate concept was to use Cowley’s prefabricated monocoque floor units made from Kerto LVL (laminated veneer lumber). Developed with Hannah Reed, the units are similar to concrete hollow core slabs, but had the concept had drawbacks when the double curved layout, the junctions with natural timber and cost were considered. The final solution which ‘ticked all the important boxes’, is a series of prefabricated ‘I-box’ beams laid radially around the curve, with a plywood deck site-applied to create a stiff diaphragm. The beams were again developed by Cowley and HRA and comprise a pair of OSB (oriented strand board) webs glued into wide top and bottom flanges of kiln dried spruce. The webs are not continuous, making the beams light and easy to handle on site as well as allowing services to pass through the voids. Sound insulation is provided in the conventional manner with insulated floor battens and high-density quilt.

The frame comprises 160 cubic metres of timber weighing about 80 tonnes. All the timber was sourced from Scotland and the borders. It took 3000 man-hours to fabricate in the Angus yard of Carpenter Oak & Woodland and 3300 man hours to erect it on site.

 

Sustainability

Sustainability was critical for the Park headquarters; the building is well insulated using sheep’s fleece insulation and constructed to high levels of airtightness. As well as the greenwood timber frame, natural materials are used widely throughout the building, including a natural slate roof finish, natural stone walling and Scottish larch cladding on the rear elevation.

The services are designed to be energy efficient. A biomass boiler, fuelled by woodchips, is used for heating and hot water. The building is naturally ventilated with automatically opening windows linked to the building management system that regulates the air temperature. To the rear of the building a reed bed area forms part of the sustainable drainage system for the headquarters. The building achieved an ‘Excellent’ BREEAM Rating of 79% at the design stage. This supported the principal expectation of the National Park that the headquarters would be an exemplar of sustainable design and demonstrate that low CO² producing buildings can be functional as well as beautiful.

 

Completion Date:

May 2008

Year Published:

November 2009

Building Type:

Office headquarters

Location:

Balloch, Scotland

Client:

Loch Lomond and Trossachs National Park Authority

Architect:

Page/Park Architects

Structural Engineer:

Main building: Buro Happold

Main Contractor:

CBC

Timber Sub-Contractor:

Carpenter Oak and Woodland

Timber Frame Connections:

SKM Anthony Hunt

Timber Wall and Floor Systems:

Hannah Reed and Associates

Timber Element(s):

Greenwood timber frame, prefabricated wall panels, diaphragm floor system, cladding

Timber Specie(s):

Douglas fir, glulam, LVL, OSB, Scottish larch

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