David Douglas Pavilion, Pitlochry, Perthshire

Introduction

The David Douglas Pavilion, a small but innovative new building constructed almost entirely of Douglas fir, is the central feature of the Scottish Plant Collectors Garden at Pitlochry. The pavilion is named after the Scottish plant collector David Douglas (1799- 1834). In 1825 he made an expedition to Canada where he identified the conifer which now bears his name and and introduced it to Europe. The Douglas fir – and the Sitka spruce which he also introduced – now form the basis of today’s commercial forest industries in Scotland.

In 2003 the garden celebrated 300 years of Scottish botanical exploration – no other nation has produced so many pioneer plant collectors. The garden commemorates Scottish collectors and demonstrates the work of associations such as the Woodland Trust, the Forestry Commission, the Scottish Wildlife Trust and the Scottish Forest Industries. It lies just behind the Pitlochry Festival Theatre and has been created from an area of mature woodland of about 2 hectares. An amphitheatre and several performance spaces have been created in the garden so that the theatre company can stage outdoor ‘promenade’ performances.in the garden so that the theatre company can stage outdoor ‘promenade’ performances.

The pavilion, reached by a winding path through the woods, sits at the top of a steep north-facing embankment overlooking the Oriental garden and giving glimpses of the distant hills. Its form is simple and organic. Curved walls enclose a large, single exhibition space on three sides; the north wall, glazed and timber-framed, has doors leading to an external viewing deck. Together, the interior space and the deck form a leaf-shape in plan.

The ridge of the pitched roof slopes upwards towards the north wall and extends beyond it, giving partial shelter to the deck. The roof is supported on a series of sloping purlins and a scarfe-jointed ridge beam which extend beyond the eaves and rest on peeled Douglas fir posts. The posts stand outside the wall and follow its curve; as a result the eaves are also curved and the resultant roof planes resemble the shape of a delicate semi-folded leaf. The peeled Douglas fir posts and the pitched roof of larch shingles blend perfectly with their surroundings, likewise the interior which is lined with mellow timber boarding.

 

Project description

‘Our brief ‘explains Robin Baker, principal of Gaia Architects, ‘was to create a focal point in the garden built entirely out of Scottish timber’. His design is modest and disarmingly simple in form, yet the structure (which he developed in collaboration with the Scottish branch of Carpenter Oak and Woodland) is a sophisticated combination of modern concepts and traditional timber joint construction.

The pavilion was constructed of timber which was grown and milled in Scotland; posts and beams, roof deck, wall frame and cladding are all made of Douglas Fir. The curved wall is formed of Douglas fir studwork lined with a double layer of OSB (oriented strand board) boards. It acts as a ring beam, bracing the posts and taking all eccentric loads so that only compressive loads are carried on them. The upper part of the wall is clad with vertical Douglas fir planks and cover strips which reduce in width where they need to accommodate the curve; the lower part is a rainscreen of horizontal 150 x 25mm boards with a 9mm air gap between, fixed to battens. The cladding is sheltered by the overhanging eaves and no preservative treatment has been used. The north elevation is framed and braced with Douglas fir members, relatively large in size to provide cross-bracing; it has a large window with a curved head, expressing the internal frame.

 

Roof

The pitched roof is formed by sloping ex 350 x 200mm purlins and a 200 x 475mm ridge beam made in two lengths joined with a double scarfed joint. The purlins extend beyond the walls to rest on a series of peeled 300mm diameter Douglas fir posts. At the top each post is planed, tapered and machined with a 50mm wide tenon; the sloping purlins are fitted with 175 x 50mm mortices which are housed into the posts.

The purlins are braced by the curved wall; they support a structural deck of 150 x 50mm t & g Douglas fir boards which rests directly on the purlins. The boards are exposed on the underside to form the ceiling of the interior.

The roof is clad with larch shingles from selected heartwood, which have pointed ends and overlap in a pattern similar to a fir-cone except at the eaves and ridge where they are rectangular. They are detailed to drain water away and are ventilated from below. The copper ridge was installed to give the shingles some protection against moss and algal growth; rainwater running off it will wash them with dilute copper sulphate.

The exterior handrail which runs at the perimeter of the deck is sawn from a naturally curved oak tree. The floor is a combination of Scottish ash and elm boards, and doors are of laminated oak.

The Douglas fir posts are flitched at their bases to circular plates bolted to a concrete pad foundation back-filled with coarse gravel to provide efficient drainage. The posts are protected from damp; at the base they are raised off the ground and surrounded with gravel drainage; at the tops they sheltered by the overhanging roof. As a result they can be used in an untreated state without external preservatives; a finish of boiled linseed oil thinned with turpentine was applied to maintain the colour.

 

The use of non-treated timber

Robin Baker and Carpenter Oak and Woodland have a strong environmental mandate which has driven the design towards the use of non-treated timber. By taking considerable care over the detailing they have ensured that water drains away from the timber and prevents it from holding moisture, while ensuring that maximum air circulation dries any timbers that become wet periodically. Maintenance of the building is also a key factor; damp leaf-litter and other debris should never be permitted to accumulate against timber elements.

Completion Date:

 

2003

Year Published:

October 2006

Building Type:

Pavilion

Location:

Pitlochry, Perthshire

Country:

Scotland

Client:

Pitlochry Festival Theatre

Architect:

Gaia Architects

Contractors:

Carpenter Oak & Woodland Company

Timber Element(s):

Structure External cladding Roofs

Timber Specie(s):

Douglas fir European larch

Awards:

Wood Awards 2003 winner commended by Dundee Institute of Architects

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