Greenwich Millennium School and Health Centre, Greenwich, London

Introduction

This school and health centre was opened in 2001. The structure is of steel and concrete but the building is particularly notable as an early use of larch rainscreen cladding in the UK. Three external elevations are finished with vertically-boarded cladding in home-grown European larch and the fourth with high performance aluminium-faced timber windows.

 

Project description

Located within the Greenwich Millennium Village, this two-form entry primary school, community hall and early years centre opened in February 2001, with the health centre following on in June 2001.

The school was designed to meet new educational targets in terms of ventilation, daylighting, acoustics, larger teaching spaces, a fully integrated IT system and designated spaces for children with special educational needs. The buildings also provide a community resource with after school clubs, a crèche, a one-stop-shop advice centre, sports facilities and, within the hall, areas for adult education and community events.

These buildings provide a new kind of facility for the community integrating education and primary health care on one site and the school was one of the first to comply with the improved energy and performance requirements of DfES.

It has a highly insulated frame structure, but also large glazed areas to the South to benefit from passive solar gain and daylighting, protected by awnings from overheating. The windows are high performance timber construction with aluminium facings to the South and the North, East and West elevations are clad with home-grown European larch boarding.

 

Rainscreen cladding

This is used as a vertical ‘board on board' form of rainscreen to the insulated framed wall. The actual design of the cladding is unusual in that, in order to provide the required visual width, the outer layer of boards consists of two closely coupled boards over a concealed centre batten.

The other edges of the board overlap an exposed narrow board between. This means that any increased dimension of the coupled boards due to moisture movement can be taken up by expansion across the surface of the recessed board.

The architect describes the cladding as a ‘wriggling timber skin' that gives a tough public façade to the School and Health Centre, in contrast to the shaded, glassy facades of classrooms and consulting rooms to the south. Windows are detailed behind the timber screen as ‘chinks' of glass seen between larch boards.

The glass is treated in different ways depending on orientation and the room behind: west and east facades include interstitial blinds; frosted or mirrored glass is employed; and louvers occasionally appear where glass is expected. A system of related details is thereby established. The protective base of the building is made of black and white brick with a continuous rail for bikes, and occasional seats built in.

At the top, the timber ‘cover boards' extend beyond the roof line, to meet a continuous horizontal protective capping. Rather than stopping the timber at the top and at the ends of the elevations, the timber cladding continues upwards to create a lighter crown to the façade, and the facing boards peel off on horizontal rails to frame external areas.

 

Species selection

Initially cedar was considered for the cladding, however following advice from TRADA, European larch was specified instead as it could be locally sourced and is more resistant to physical damage, important in a school environment. This was an early use of larch for cladding in this country, although long used in the rest of Europe. With sapwood omitted European larch is rated a moderately durable wood and is suitable for use in cladding without preservative treatment. In this case, as there was limited amount of timber available from the local source, it was decided to treat the wood rather than omit the sapwood. Despite this, the boards were left unfinished to bleach and weather naturally.

 

Installation

As part of the design it was envisaged that the cladding would be installed as prefabricated panels, with site fixed ‘cover boards' running the full length of the building between the windows and the panels. However the subcontractor chose to fabricate the timber panels on site, using workbenches and fixing directly onto the building. The panels are made up of straight, or curved horizontal rails to a given radius, and vertical board on board. Panel facing boards are fixed using stainless steel annular rink shank nails. Contractors generally like to use nail guns, but in this instance the nails were carefully hammered into place resulting in flush and virtually invisible. The full length cover boards are fixed with carefully set out expressed fixings; stainless steel pan head stainless steel screws with stainless steel washers, allowing them to be removed for future maintenance, if necessary.

 

Architect's comment

The timber moisture content was high when erected, and we were concerned that boards might split. But we are pleased with the end result; the larch has bleached consistently without staining or blackening and no maintenance has been required since the original installation.

 

Client's comment

The cladding has visually weathered attractively and stood up well, particularly at low level to the usual "wear and tear" of a school environment. We have not as yet had any maintenance costs related to the boarding. Our only problem with the detailing has been where the cladding crosses the windows as this makes replacement of broken glazing more difficult.

Completion Date:

2001

Year Published:

July 2006

Building Type:

School & health centre

Location:

Greenwich, London

Country:

England

Client:

English Partnerships

Architect:

Edward Cullinan Architects

Sub-Contractor:

Swift Southern

Timber Element(s):

Exterior rainscreen cladding

Timber Specie(s):

Larch, European

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