Plant-based materials such as hemp-lime 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.
In the UK alone construction is responsible for around 300m tonnes of carbon dioxide emissions, which is almost 47% of the UK’s total. Of this, around 50m tonnes is embedded in the fabric of buildings. Making one tonne of steel emits 1.46 tonnes of CO2 and 198kg of CO2 is emitted make one tonne of reinforced concrete.Whereas 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 plants can be converted into building materials, we are in a win-win situation. Plants use the energy of the sun to convert atmospheric CO2 and water into hydrocarbons – the material from which plants are made. The plant acts as a carbon store, sequestering (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.
To build using hemp, the woody core 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 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, where the materials have absorbed more CO2 than is consumed during construction.
The three-storey archival store that the Science Museum in London 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.
The new HIVE building – a £1m project funded by the Engineering and Physical Sciences Research Council – has been designed as a platform for research projects into this kind of sustainable construction. The HIVE has a purpose-built flood cell, which will also support research into creating buildings and building materials that are more flood-resilient – a valuable resource in these times of climate change induced adverse weather conditions.