Top of the tree

Introducing vegetation into urban environments is a common strategy to mitigate the effects of environmental destruction and climate change. But it’s difficult to scale: “It can’t be achieved just by planting trees, or by individual façade and rooftop greening projects, so additional solutions are urgently needed,” explains Nicola Stattmann, co-founder of OMC°C. “We need fairly large structures to generate the necessary amount of shade and biomass.”

While large structures are usually the remit of architects, OMC°C developed its vertical greening system in partnership with design studio Diez Office, usually known for its elegantly functional furniture. “The solution needs to be modular, suited for serial production, and easy to use and maintain – this is the expertise of the product designer,” Stattmann says. Working together for two years, the two offices had done a few experiments, but were still in search of a suitable material for a low-carbon, sustainable structure.

Enter AHEC, the trade association that champions the virtues of American hardwoods worldwide, often through ambitious design commissions. It has been on a mission to promote the use of red oak, an underutilised species which represents 18% of overall timber resource in the US. For Vert, AHEC teamed up with Swiss timber construction experts Neue Holzbau to develop red oak ‘glulam’ – an engineered material made from multiple grain-aligned layers of timber, finger-jointed and laminated together for greater strength and stability. 

As David Venables, AHEC’s European director, describes, glulam made from hardwood, such as red oak, is expensive and requires care in manufacturing, but it is stronger than softwood equivalents and offers the opportunity to reduce the size of construction elements. To establish red oak glulam’s suitability for practical applications, Neue Holzbau conducted a series of delamination tests and tension tests on finger joints.

The material’s qualities certainly enable Vert’s triangular form, which minimises material use while withstanding heavy winds and bearing the weight of the plants. The structure also includes hammock-like seating, made from red oak glulam and biodegradable netting, while the deck floor underneath is lined with red oak planks, thermally modified to enhance durability and attain a rich brown hue.

The 20-ish plant species within Vert include morning glory, cheese plants, black-eyed Susan and night blooming moonflower. All are locally-sourced and selected according to three criteria: they grow quickly, can survive intense sunlight and high temperatures, and produce nectar or pollen for the benefit of insects. The project partners estimate that Vert will cool its surrounding air by as much as 8ºC, and cast four times more shade than a 20-year-old tree.

They are already considering Vert’s afterlife. “It’s a continuing experiment, and we would love to put it up again for a number of years,” says Venables. “Due to the very short installation window at Chelsea, the plants have to be pre-grown, but perhaps in future we can grow them in situ, which allows for greater biodiversity.”