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Woodland Trust HQ, Grantham, by Feilden Clegg Bradley Studios

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Feilden Clegg Bradley Studios’ low-energy construction and simple plan make this an office you want to work in, writes Kester Rattenbury. Photography by Peter Cook

At first sight, I’ve learned to expect to be underwhelmed by Feilden Clegg Bradley Studio’s (FCBS) mild, well-made, buildings. And to ignore my first reactions, and be absolutely gobsmacked by the extent of creativity and innovation that goes into making such exceptionally good, pleasurable places to be in, even on the most unpromising of sites. This is one of those projects.

Think Woodland Trust HQ and you’re probably imagining a delicate, responsive building in a fragile sylvan setting, not a low-grade commercial strip on the edge of Grantham.

But the Woodland Trust has had its HQ just across the road, in a brick-panelled industrial building, for years. It considered going sylvan, but it would have meant lots of relocation and driving – not so green. A site came up just over the arterial road, squeezed between a new warehouse and housing, next to the ten-pin bowling. Perfect. The mild, beautifully made exterior reads pretty normally for its site – it is, in its own way, a classic bit of strip-palazzo architecture on a car park in a typical English ribbon development – albeit in timber, exquisitely made, and with silver birches in the car park. It is, in all sorts of ways, respectful of its environment.

Oddly there are some metaphorical aspects to this. Despite the big, almost simple front, the building’s plan is based on a cranked spiral (a fern frond metaphor), winding outwards from the ‘woodland glade’ through which you enter. The facades are fenestrated and clad in uneven vertical strips, to suggest a birch grove. If this seems like an awkward cross between simple functionalism and hefty metaphor, in reality it works beautifully.

From that car park front, you go down the side of the building toward a gate that leads into a different scale of space; an irregular courtyard landscaped with birches, benches and ferns; an outside social space winding up to bike stores and an outdoor meeting area.

From this scale it’s immediately human. The long, south-facing strip windows are varied in height and width and with different opening components and brise soleils. And, through them you see this layered, shaded view, sometimes straight through the building to the car park and trees on the other side. This ‘view through a forest’ analogy does work, and surely because of the absolute care with which it’s made and detailed, from close to large scale.

This is, tangibly, a socially planned building. The Woodland Trust’s old offices were compartmentalised. Here, it’s the opposite. The outside, social ‘glade’ opens straight into another social ‘heart’ – the big volume of the entrance, going straight up to the high, sunlit roof, overlooked by galleries on both the upper floors. This is clearly not just for show. On one side, there’s an open kitchen and education area, where you’d usually have art or reception; on the other, there’s the big open stairwell between you and the main office areas. It’s simple colours: white, grey, muted timber, lit by flashes of bright green.

It’s clear you are meant not only to work here, but make yourself comfortable. From inside the offices, the building performs one of those minor miracles – it re-crops the immediate environment to give lovely views: the mildly rolling wooded horizon; the church spire; the rooftops of a nice English country town.

There are a number of construction innovations. Because of the value of concrete soffits for thermal cooling in office buildings, many ‘environmentally’ conceived office buildings often use concrete frame construction, despite its embodied energy. But this brief implicitly suggested timber construction, far better in carbon terms. In particular, FCBS wanted to try new cross-laminated timber construction; you cut holes for windows and doors ‘just like a cardboard model’, project architect Will Garner explains.

The issue was how to combine this with concrete soffits. The result, ‘concrete radiators’, is a major innovation, developed with Max Fordham and Atelier One. They calculated the area of concrete needed for the soffits (to CIBSE requirements, specific to the region), then integrated this with those big timber slabs. The result is a composite panel: two 2m-wide slabs of concrete were fixed to the underside of the 2.4m-wide, 15m-long, cross-laminated timber panels. Besides radiant cooling, the concrete component, ribbed and strongly reinforced, strengthens and stiffens the timber, so that the panels (162mm timber, plus 250mm downstands) can span the 15m floorplate with just one row of super-slim columns. They’re very stiff, very strong, with very little movement, and very quick to build. The panels are taped and sealed, and make the construction super-airtight, too – four times as much as the Regs require.

The client did take some convincing about the construction. The team built a full-size prototype to test the structure (which deflected far less than expected; 3mm when it was designed for 10mm) and go through elaborate costing and tendering procedures to prove that it wasn’t going to cost more.

The painted ‘radiators’ help bounce light into the building – part of a lovely light condition. There is a 4m floor-to-floor height (rising to 5m on the top floor) with those long strips of windows on both sides – you can see right through, and there’s plenty of light around. The windows at the top are BMS-controlled so as to draw air through the building, helped by the external cowl. The windows you can reach are manual, and it’s strange how strongly that sense of freedom and control registers on you as you come in. Then the desks are (astonishingly, this is also unprecedented) lit so as to be task and desk-use specific with manual control options – not the standard office ‘even spread’. Non-working areas – the stairwell and entrance – are flooded with sunlight to add ‘sparkle’.

The 11.5° pitch faces due south to accommodate photovoltaic panels at some point in the future. All the computing power is housed in the server area where the heat can be captured and re-used through a free-cooling heat exchanger, with only low-energy terminals and screens in the office area.

But the vast architectural saving is on the energy used in construction. FCBS has worked out that the carbon saved by not using concrete frame construction is the same as the first nine years of the building’s operation.

What is exemplary about FCBS’s work is the extent to which the human experience and the environmental concerns are simply the same – they save energy, innovate and make the building a nicer place as a wholly integrated thing: views, spaces, colours, light and environment.

The timber construction, for instance, is painted on the inside with a specially developed white varnish,so the timber acts as a membrane and moisture should take the easy route outwards through increasingly permeable layers: insulation, battens and untreated larch slats.

But the paint makes a very nice surface too: light and soft, but without what Garner calls the ‘sauna effect’. It did mean the builders had to treat the timber with kid gloves, since any marks, writing or damage would have formed part of the permanent ‘wallpaper’ of the building. In fact, the contractor had to work to pretty well ‘zero tolerances’ throughout, says Garner, and somehow did so.

But that seems to be typical of this project – it took a huge amount of effort and care, but this really pays off. The client got exactly what they asked for: something inspirational, innovative and frugal – exemplary and do-able, at £167/m2. It does what FCBS says, too: innovation using normal things like wood and paint. The firm is now using cross-laminated timber construction with more specialised paints on four other buildings, including a neonatal unit, a library and a primary school.

In the end, even the outside of the building won me over. Its sloping form fits its unpromising mixed bag of neighbours: from the courtyard its ‘woodland glade’ views of trees and reflections are oddly convincing. Walking back to the station, I thought the old ribbon development looked okay too. Busy, varied, walkable, even kind of charming. FCBS had made the whole place feel better.

Project data

Start on site: October 2009
Project completion: October 2010
Gross internal floor area: 2,728m2
Form of contract: Traditional SBC05
Total cost: £5.1m
Cost per m2: £1,700
The Wooodland Trust
Project manager: Buro Four
Architect: Feilden Clegg Bradley Studios
Structural engineer: Atelier One
Services engineer: Max Fordham 
BREEAM assessor: Max Fordham
Landscape architect: Grant Associates
CDM co-ordinator: PFB Construction
Quantity surveyor: Ridge
Building control: Approved Inspector Services

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