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THE INDOOR - OUTDOOR RELATIONSHIP WAS KEY

TECHNICAL & PRACTICE

Timber cladding has been used effectively on two very different nursery school sites in London.

Two recent nurseries have used timber cladding as a natural material suitable for a nursery brief and for reasons of speed and economy - with very different results. The Children's Garden Early Years Centre is a Steiner-inspired nursery for 43 children on the University of East London (UEL) campus, by Camden-based practice Arts Lettres Techniques. Ambler Children's Centre by Potter and Holmes Architects provides nursery accommodation for 60 children on the site of an Islington primary school in an unusual pairing of nursery and primary education. As one might expect, the indoor/outdoor relationship was important in the development of both schemes.

The UEL project was completed within an extremely tight schedule, as the architect was appointed in December 2005 and the nursery had to be ready for occupation in September 2006.

An important aspect of the design was a shallow plan, oriented to capture the prevailing wind, with operable rooights and porous circulation to facilitate cross-ventilation. The use of prefabricated steel-framed modules, which were partly fitted out off-site, was key to meeting the tight deadline. To lower costs and keep the nursery's carbon footprint in line with UEL's sustainability policy, recycled steel-framed modules were used. Not surprisingly, an Arup study, 'CO 2 Emissions from Use, Scrapping and Manufacture of Modular Buildings', has shown that recycling older units and updating them to comply with the new Part L, rather than simply scrapping them, was the best way forward for the modular building industry.

The nursery comprises 13 3 x 7.3m modules set end-to-end. The lightweight construction was advantageous on the dockside site of 'made up' ground because shallow concrete trench foundations could be used rather than piles, which meant the membrane would not be punctured over the potentially contaminated ground, a particularly critical issue for a nursery.

The standard composite panels were relined inside and out to alter their visual appearance and provide the necessary acoustic isolation from nearby City Airport. Internally, the units were lined with timber studs and 24mm acoustic insulation and plasterboard.

Windows and some internal partitions were fitted in the contractor's yard, which required careful setting out so that the modules could be transported individually to the site.

Externally, 80 x 32mm vertical boards of Scottish larch, chosen for its lively texture and also for its reduced transport miles, have been fitted to the modules, packed out so that the wall appears to be 300mm thick to make the building feel more solid and permanent. Director Luisa Auletta explains that the rougher quality of Scottish larch suited this particular application, which did not require tight joints because the timber provides a visual - not a weather - screen. The larch cladding is spaced to avoid the use of any cut boards, and the joints are slightly wider on the upper band of cladding, creating a subtle visual effect. Red cedar was ruled out because it is 'visually dead' and because of the embodied transport miles. Siberian larch was considered because of its tighter grain but also ruled out on transport miles, and sweet chestnut from Kent was not available within the time constraints.

The larch was detailed to ensure even weathering for a uniform look in keeping with some nearby rendered facades by Edward Cullinan. A crisp roof detail with no projection eliminates the possibility of stains from projecting eaves, and the projecting drip of the pressed metal window sills is held 10mm behind the cladding for the same reason.

Potter and Holmes' Ambler nursery is located in a very different context, within the site of a Victorian board school. New entrances to the site were created to serve the children's centre and a new outreach centre which operates a crèche in a refurbished dental laboratory on the site. The constraints of the site and the desire to make the most of an existing wildlife garden to the north determined much of the final layout. Teaching spaces are arranged along either side of a multi-purpose corridor, and ventilation is provided by operable windows and a stack effect through rooights, which also provide additional daylight to the deep plan. Project architect Lucy Grindley explains that lighting is arranged in tiers to allow low light levels at the back of the rooms to be boosted on dull days without turning all the lights on. A child-friendly 275mm-high bench detail was incorporated around the perimeter of the building, which also enables the timber construction and damp-proof coursing to be kept 150mm minimum above ground level.

Natural materials, such as marmoleum on the oor and Warmcell in the roof, were specified where possible, with advice from the Green Register. Grindley explains that the practice now views the project's U-values (walls: 0.35, roof and oor: 0.25, windows and doors: 2.0) as 'last year's values', and current projects are achieving 0.1 in walls, roofs, and oors. The building is clad in cedar, with a deep overhang (300mm minimum) to provide solar shading in summer and protect the walls from rain damage.

The acoustic requirements of BB 93 for sound insulation, reverberation time and internal ambient noise were met by using British Gypsum Rigitone on the ceilings in the teaching and circulation spaces. Rigitone has irregular circular perforations which add a whimsical touch to the ceilings.

Surprisingly, if one compares approximate costs for the two projects, the Ambler Nursery comes in slightly below UEL despite UEL's use of the prefabricated modules. Ambler, which is roughly 400m 2, works out to roughly £1,600/m 2, while UEL's 300m 2 comes in at £1,800/m 2. Despite their similar briefs and not dissimilar square-metre costs and their common use of timber cladding, these two projects differ greatly in their architectural expression. Each, within its own context, creates an inviting and humane environment for children to spend their days.

See further illustrations overleaf.

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