Bio-based construction materials for the building industry

Materials World magazine
,
2 Aug 2016

Peter Wilson believes bio-based construction materials could play a role in the future of the building industry, and reports on how they are already being used.

Something is changing in the world of architecture and construction. Long considered the stuff of eco-warriors, a whole range of bio-based materials are beginning to be used on some highly sophisticated buildings. Sophisticated, that is, in their low energy, carbon storage and life cycle credentials rather than the conventional use of that word as an indicator of complex technical specifications and high-tech components. Yes, we’ve all seen the worthy types on Grand Designs self-building the homes of their dreams from straw bales and mud with all the attendant imperfections in construction, but a number of recent developments in architectural thinking are likely to radically alter our perceptions in this area.

It is not only the world of domestic buildings that is changing – large projects are making greater and more effective use of bio-based materials. But having maligned Grand Designs, I need now to give some credit to Kevin McCloud for establishing Hab, a development company that provides Custom Build (an expanded form of self-build) eco-homes around the country. The Triangle project in Swindon, a joint venture between Hab and West Country housing agency Green Square to create 42 housing units around a central landscaped area, is a good example of a low-energy, bio-based approach being applied at scale. Designed by Glenn Howells Architects, UK, the firm responsible for the construction of the remarkable gridshell roof of the Savill Building in Windsor Great Park from trees grown within 600 meters of the site, this multi-award winning housing project is built using Tradical Hemcrete, a bio-composite material made from hemp shiv (the woody core of industrial hemp) and a lime-based binder. Aside from its ability to lock up significant volumes of atmospheric carbon dioxide, the material provides high levels of thermal insulation and thermal inertia, which, in combination with lime-based renders and plasters, delivers a stable internal environment. 

The passive approach

Passive building is a standard that is truly energy efficient, comfortable, affordable and ecological. These examples are not only passive in terms of their technological approach, but passive because you wouldn’t know from first sight that these materials have been used in preference to conventional masonry solutions. A more visible – and striking – demonstration of the use of locally available materials is Naturum, the visitor centre at Lake Tåkern, Sweden – a popular nature reserve and the annual nesting habitat for over one hundred species of birds. The building was designed by renowned Swedish architect Gert Wingårdh, who described it as ‘quiet architecture, using traditional local materials to break new ground with crystalline geometry’. The centre’s asymmetric form folds around an entrance courtyard with traditional building techniques evident in the use of locally-cut golden reeds in the walls and roof. The reeds have weathered to grey over time and now match the nearby bird-watching tower, Wingårdhs, completed in 2009. The building’s thatched exteriors reflect the typical temporary hides constructed by bird-watchers, as well as providing nesting materials and hiding places for small birds. Quiet architecture it may be but, despite its traditional cladding, this is very much a dynamic modern building. 

The latest and most comprehensive use of bio-based materials in a large, non-domestic building is undoubtedly the new Enterprise Centre at the University of East Anglia, UK. The building’s radical design approach has delivered the client and architect’s aim of achieving a BREEAM Outstanding rating as well as full Passive House Certification, through innovative use of vernacular techniques and locally available materials. The building’s client, the university’s Adapt Low Carbon Group, led by CEO and plant scientist Dr John French, asked what seemed to be a very simple question, ‘Why had no-one previously tried to create a large scale natural bio-building?’ Well, now they have, and it sends out a strong message to every university in the country – that our academic institutions should be leading in the R&D of new construction approaches and technologies through the refurbishment and expansion of their own estates. Too often, we see variations of commercial development approaches being applied by a client group that, by its very nature, has no requirement to build speculatively or for subsequent sale, but has specific needs that – if properly considered – could inform and support significant academic research programmes. 

The building itself

Completed by architects Architype, UK, the building forms a gateway to UEA’s Norwich Research Park and contains a 300-seat lecture theatre, an innovation lab, teaching and learning facilities and flexible workspaces, business hatcheries and incubator units for SMEs and start-up businesses in the low-carbon sector. What better place to apply bio-based materials and technologies in the creation of what has been described as ‘the most sustainable large building in Britain’?

It makes good use of thatch, a traditional building material in East Anglia and, in this instance, made from local straw varieties such as Foster Special, Maris Huntsman and Yeoman Wheat. The radical part is that the thatch is used in prefabricated form – 300 panels (in 14 variations) put together in local joinery shops by six thatchers during winter months, when they would normally have no opportunity to work. Thatch, of course, is not known for having an extended lifespan. But, in a building required in its brief to stand for more than 100 years, its use in vertical rainscreen cladding panels suggests it could last well over 50 years, with those requiring renewal simply unclipped and replaced. Less visibly, the roof makes use of local reeds from Woodbastwick, on the edge of the Norfolk Broads, and from the RSPB’s Dingle March reserve at Saxmundham.

The Centre’s timber frame also charts new territory – it is largely manufactured from Corsican Pine grown in Thetford Forest, 30 miles from the Enterprise Centre site. This particular species is more conventionally used for fencing and decking but, following initial sawing at Thomson Sawmills north of Norwich, the material was sent to timber frame specialist Cygnum’s factory to be kiln dried, planed and strength graded to meet the structural engineer’s design calculations. This is ground-breaking and creates new, higher-value possibilities for a species normally reserved for low grade purposes but that can now contribute a local solution to increasing demand for housing in the region.

The walls use a twin-frame system into each structural stud plane, filled with 140mm of cellulose insulation produced from recycled newspapers. With breathable wood fibre to the exterior and 18mm oriented strand board (OSB) acting as an airtightness layer, the building achieves a remarkable 0.21 air changes per hour, while the thermal insulation strategy that delivers a U-value of 0.11 W/m2K results in a minimal energy requirement of ≤ 120KwH/m2 – meaning it needs virtually no heating. 

The range of possibilities

The list of bio-based materials used in the buildings goes on. Larch sourced from Brandon Fields Estate, Suffolk, has been fabricated into glulam beams, and the first floor meeting rooms and board rooms are each clad in a different material – reed, earth and clay plaster, nettle fabric – but eschew any sense of being hand-knitted. Even the corn dollies at window reveals – while throwbacks to traditional architecture – are a tried and tested solution for finishing tight, visible corners. 

Do these examples offer new avenues for natural building technologies and indications of possible new bio-based construction components and systems? The answer must be yes, with the added bonus that craft skills can be employed to deliver solutions normally associated with serial production processes. The message is clear – true sustainability doesn’t stop at the outer skin of a building, it is reflected in design approaches that recognise the need to use local resources and that help sustain good quality employment in local communities. Innovation from the country’s academic, design and engineering communities in the use of bio-based materials has the potential to impact positively upon the UK’s skill base and provide it with new opportunities suited to 21st Century environmental imperatives. What’s not to like? 

Peter Wilson is an architect and managing director of Timber Design Initiatives Ltd. The company exists to deliver new, Europe-wide approaches to education, innovation and demonstration of best practice in the use of wood in architecture, design and construction through applied research collaborations between academia and industry.