Thermally-modified lumber for outdoor applications


Asif Khan Architects design elevated playground for school in thermally modified hardwood.

When the children at Chisenhale Primary School in East London come rushing outside to play, they know exactly where they are going. They make a beeline for the elevated play structure on one side of their playground, running up either side of a mound, assisted by ropes or handholds, or using a climbing net.



This simple, elegant timber-clad structure is a far cry from the off-the-shelf play equipment that head teacher Helen James believed she needed to address the problems of her largely dull and very small playground. “I said that I just wanted it to be bigger,” she says. In the manner of good head teachers, she called on the expertise of her parents, in this case architect Asif Khan who has two children at the school.


He soon persuaded her that a bespoke structure could be better and they set about developing a design and raising money. The result is a surprisingly ‘adult’ looking piece of architecture, a rectilinear box where the only colour comes from the warm tones of the thermally modified timber. It is marvellously flexible, a place where the children can play in their own way, rather than following prescribed activities. And this was something, said James, that the children understood immediately, knowing instinctively how they wanted to use the space.


The structure is of galvanised steel, clad in slats of thermally modified tulipwood and with beams and flooring in thermally modified ash. Asif Khan was keen to use timber, because of its visual warmth, a contrast with the hard playground and the brick of the school building and surrounding housing. “I was keen to introduce a natural material that would age and grow with time,” he says.


He had seen the American Hardwood Export Council’s (AHEC’s) use of thermally modified timber in a project for the London Design Festival, in particular a contemplative shed that was designed for use by fashion designer Paul Smith by Nathalie de Leval. “When we decided that we wanted to work with wood,” Khan says, “I felt that they would know technically what would work outside.”


Both he and Helen James are great fans of the tulipwood because it is so smooth to the touch – an important factor when considering how often small hands are going to be gripping it. The thermal modification, as well as changing the colour to make it darker, makes timbers that would not otherwise be durable for use outside stable and long-lived.


AHEC is particularly keen on the use of tulipwood because it is one of the most abundant timbers in U.S. hardwood forests, so there is a strong environmental argument for its use – the resource is increasing much faster than it is being harvested. Ash already widely used for thermal modification. Both are lighter in weight than traditional durable hardwoods such as oak, allowing the entire structure to be more lightweight.

Carpentry company Aldworth James & Bond had not worked with thermally modified timber before but found it easy to use. They worked out a method of using a CNC (computer numerically controlled) machine to cut all the individual elements, making allowance for example for the rebates where the slats fitted to the steel frame. In this way it could make the panels relatively rapidly and simply.

The play space is modular and has been designed so that it could extend, possibly to the roof of a nearby outbuilding, where an additional classroom could be built for specialist activities.

Text: Ruth Slavid

Photos: Helen Binet

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