Dr Mike Lawrence is Director of the University of Bath’s Building Research Park (BRP)– aimed at reducing the carbon footprint of buildings. The following blog appeared on the Guardian Sustainable Business website on 25 September 2014 to coincide with the launch of the BRP's opening.
So how can growing buildings help with climate change, you may ask? Well, it’s all about renewables and ‘sequestered carbon’. The Department for Business, Innovation and Skill’s 2010 report on Low Carbon Construction concluded that construction was responsible for some 300 million tonnes of carbon dioxide (CO2) emissions, which is almost 47 per cent of the UK’s total emissions. Of this figure some 50 million tonnes is embodied into the fabric of buildings. It uses 1.46 tonnes of CO2 to make 1 tonne of steel and 198kg CO2 to make 1 tonne of reinforced concrete. One square metre of timber framed, hemp-lime wall (weighing 120kg), after allowing for the energy cost of transporting and assembling the materials actually stores 35.5kg of CO2.
If we can convert plants into building materials, we are in a win-win situation. Firstly, plants use the energy of the sun to convert atmospheric CO2 and water into hydrocarbons – the material that plants are made from. The plant acts as a carbon store, sequestering or ‘absorbing’ atmospheric CO2 for as long as the plant continues to exist. This CO2 is only re-released when the material is composted or burnt, and the great thing is that through replanting it you can re-absorb this CO2 annually, in the case of straw or hemp, or every decade or so in the case of timber, rather than the 300 million years that it takes to recycle coal or oil.
Secondly, plant based materials can be used to make high performing building envelopes, protecting against external weather and making a building more comfortable, healthy and energy efficient to live in.
Not only can they be used as insulation materials, displacing oil-based alternatives such as polyurethane foam, but they also interact with the internal environment in a way that inorganic materials just can’t do. This is because they are ‘vapour active’. Insulating materials such as hemp-lime, hemp fibre and wood fibre are capable of adsorbing and releasing water vapour. This is doubly effective, because not only can they act as a buffer to humidity (taking moisture out of the air), but they also stabilise a building’s internal temperature much better through latent heat effects (energy consumed and released during evaporation and condensation within the pores of the material).
To build using hemp, the woody core or shiv of the industrial hemp plant is mixed with a specially developed lime-based binder. Factory-constructed panels are pre-dried and when assembled in a timber frame building, the hemp shiv traps air in the walls, providing a strong barrier to heat loss. The hemp itself is porous, making the walls well insulated while the lime-based binder sticks together and protects the hemp, making the building material resistant to fire and decay. As the industrial hemp plant takes in carbon dioxide as it grows, and the lime render absorbs even more of the climate change gas, hemp-lime buildings have an extremely low carbon footprint.
In this way bio-based materials can be used to construct ‘zero carbon’ buildings, ie. buildings where the materials have absorbed more CO2 than is consumed during construction. By applying PassivHaus principles (the voluntary industry standard for low-carbon design) to bio-based buildings, a building’s energy use once inhabited can also be reduced to minimal levels. This is a true ‘fabric first’ approach, where the fabric of buildings passively manages energy consumption, rather that purely relying on renewables such as solar panels and ground source heating systems which have a more limited life-span and have the potential for failure.
I worked on a project recently for the Science Museum to reduce the high energy cost of archival storage. They needed to have large enclosures kept at a steady humidity and temperature to ensure that items ranging from the first edition of Newton’s Principia through to horse drawn carriages and even Daleks do not deteriorate. Normally this uses energy intensive air conditioning systems.
The three storey archival store that the Science Museum built in 2012 using a hemp-lime envelope was so effective that they switched off all heating, cooling, and humidity control for over a year, maintaining steadier conditions than in their traditionally equipped stores, reducing emissions while saving a huge amount of energy.
In the BRE Centre for Innovative Construction Materials (BRE CICM) at the University of Bath we are working on some very exciting EU funded projects to increase the use of low carbon construction solutions. Research programmes aimed at producing certified construction systems using straw bale and hemp-lime respectively have potential to transform the construction industry in the UK, introducing such revolutionary sustainable products to the mainstream sector.
Other research we are carrying out is finding better ways to passively improve the internal air quality of buildings by using improved bio-based materials to interact with air borne pollutants, removing them from the building.
The new HIVE building - a £1m project funded by the Engineering and Physical Sciences Research Council (EPSRC) - acts as a platform for research projects of this type. The HIVE also has a purpose built flood cell, which will support research into creating buildings and building materials which are more flood-resilient – a valuable resource in these times of climate change induced adverse weather conditions.
In practice what this all means is that the industry and government now need to embrace the opportunities presented by bio-based construction materials to reduce emissions. Good quality domestic housing can be built out of structural timber with a bio-based insulating envelope such as the ModCell® system using straw; the HempCell® system using hemp-lime, or other systems using wood fibre or other cellulose fibres.
With domestic housing high on the Government agenda, surely it is time the construction industry recognised the economic and environmental benefits of bio-based construction materials and became less reliant on depleting resources such as oil and steel.
Dr Mike Lawrence is Director of the Building Research Park, the University of Bath’s new research centre for sustainable construction materials and systems which opens on 25 September 2014. Anyone interested in finding out more can contact firstname.lastname@example.org , visit www.bath.ac.uk/brp or follow @HiveBRP on Twitter.