Harcourt Arboretum has installed the UK’s first carbon neutral 'eco arc’, made from sustainable materials by two Oxford University graduates. The Arboretum in Nuneham Courtenay stretches 130 acres and contains some of Britain's oldest redwoods among 13,000 native trees and 30 acres of wildflower meadows.

Silver birch and bracken understorey at the Harcourt Arboretum  
The Arboretum’s new eco-friendly ticket office and gift shop arriving. The building is clad at the front and back with cedar boards and has a sedum roof, all insulated with sheep’s wool
 
By Richard Lofthouse
On a blustery, damp day, a transporter lorry turns up at the University’s Harcourt Arboretum at the village of Nuneham Courtenay, four miles south-east of Oxford towards Reading.
 
Atop sits a rather elegant building that is lifted gently onto a concrete base, already plumbed up for a huge underground heat exchanger that squiggles invisibly among the tree roots for thirty metres, allowing cool air in the summer and warm air in the winter.
 
This is the very first installation of a Green Unit by a local, Chiselhampton-based company of the same name; and as the unit’s designer Phil Clayden (Blackfriars, 1995) tells me, the correct term is arc modular building system.
 
The building will function as a welcome centre, ticket office and gift shop for the Arboretum, but my working hypothesis is that it’s also the twenty first century shepherd’s hut/writing bolt/log cabin that we all dream about.Silver birch and bracken understorey at the Harcourt Arboretum
The office is designed and manufactured by Green Unit, a company set up by two Oxford graduates 
It is also more than that. For instance, the unit you see here cost £45,000, and it weighs 4.6 tonnes. It is claimed to last at minimum 100 years, and by ‘twenty first century’ we mean an exceptional combination of energy saving ‘performance’ (buildings, like cars, are held to ‘perform’ in this sense) and quality, drawing heavily on the German Passivhaus movement, which abhors drafts the same way that nature abhors vacuums.
 
The unit is also a laminated, stressed skin module, which means that layered plywood is applied to ribs and the outer ‘skin’ has a lot of mechanical strength; and modular because it can be made larger and smaller through the addition of modules, to cater for everything from a beach hut to a family home. From the roof to the triple-glazed, burglar and cold impervious windows, this couldn’t be further removed from a traditional shepherd’s hut. Possibly the only thing they have in common is the capacity to house a wood burning stove.
 
‘We are the centerpiece in the Ideal Home Show at Olympia,’ notes Clayden, noting that for the show he has built a two-storey house that will be erected on site in less than a day. 
 
The main weakness I identify is the use of sheep’s wool insulation. What about moths, I ask? There was a recent, much publicised disaster where a chap installed wool and got a million moths instead. ‘It’s treated permanently against moths, and it is a relatively thin skin and not the only insulating material,’ says Clayden.Silver birch and bracken understorey at the Harcourt Arboretum
 Silver birch and the bracken understorey at the Harcourt Arboretum 
Green Unit is co-led by Jonathan Finnerty, a successful digital media entrepreneur whose alma mater Oxford Brookes helped to develop the unit. While we’re gazing on at the unit's lowering into its resting place, he explains that they are actually made in Chiselhampton, not ‘bought in’ from Finland or Germany or wherever; and that if things go to plan, a certain volume of orders will enable them to reduce the cost from £1,800-£2,000 per square metre to £1,500.
 
Apart from the Ideal Home Show, Clayden says that they want to build an eco-school next, “designed to facilitate an brilliant new educational approach developed by a local head teacher.”
Harcourt Arboretum has installed the UK’s first carbon neutral 'eco arc’, made from sustainable materials by two Oxford University graduates. The Arboretum in Nuneham Courtenay stretches 130 acres and contains some of Britain's oldest redwoods among 13,00 
The Green Unit is light years ahead of Wimpey, Barratt et al, and mercifully shuns the ubiquitous ‘L’ word (‘luxury’). It strikes out on its own, in defiance of the sorry history of building standards in the UK building trade. Yet for all that I wonder if the ever-conservative British public will be able to conceive of it as more than a holiday let/granny flat. Time will tell.
 
www.greenunit.co.uk
 
Images: Oxford University Images, Rob Judges, Richard Lofthouse

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