8/11/2019 Growing our way out of climate change by building with hemp and wood fibre

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Growing our way out of climate change by building with

hemp and wood fibre

By Mike Lawrence

Source:ÃÂ theguardian.com

From domestic housing to the Science Museum, plant-based construction materials cut reliance onscarce resources and build healthy, efficient and zero carbon buildings

Houses made from hemp could mitigate climate change. Photograph: Roy Morsch/Corbis

How can buildings help with climate change? ItâÂÂs all about renewables and Ã¢ÂÂsequestered carbonâÂÂ.

The Department for Business, Innovation and SkillsâÂÂà2010 report on Low CarbonConstruction Ã concluded that construction was responsible for around 300m tonnes of carbondioxide emissions, which is almost 47% of the UKâÂÂs total. Of this, around 50m tonnes isembedded 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. One square metre of timber framed, hemp-lime wall (weighing 120kg), afterallowing 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. Plants use the energyof the sun to convert atmospheric CO2 and water into hydrocarbons â the material fromwhich 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, and thegreat thing is that through replanting it you can re-absorb this CO2 annually, in the case of straw orhemp, or every decade or so in the case of timber, rather than the 300m years that it takes torecycle coal or oil.

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Secondly, plant based materials can be used to make high performing building envelopes, protectingagainst external weather and making a building more comfortable, healthy and energy efficient tolive in.

Not only can they be used as insulation materials, displacing oil-based alternatives such aspolyurethane foam, but they also interact with the internal environment in a way that inorganicmaterials just canâÂÂt do.

This is because they are âÂÂvapour activeâÂÂ. Insulating materials such as hemp-lime, hempfibre and wood fibre are capable of absorbing 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 alsostabilise a buildingâÂÂs internal temperature much better through latent heat effects (energyconsumed 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 speciallydeveloped lime-based binder. Factory-constructed panels are pre-dried and when assembled in atimber frame building, the hemp shiv traps air in the walls, providing a strong barrier to heat loss.

The hemp itself is porous, meaning the walls are well insulated while the lime-based binder stickstogether and protects the hemp, making the building material resistant to fire and decay. Theindustrial 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.

Building with hemplime.ÃÂ Photograph: University of Bath

In this way bio-based materials can be used to construct âÂÂzero carbonâ buildings,where the materials have absorbed more CO2 than is consumed during construction. ByapplyingàPassivHaus principles Ã (the voluntary industry standard for low-carbon design) tobio-based buildings, a buildingâÂÂs energy use once inhabited can also be reduced to minimallevels. This is a true âÂÂfabric firstâ approach, where the fabric of buildings passivelymanages energy consumption, rather than purely relying on renewables such as solar panels andground source heating systems, which have a more limited life-span and 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 ensurethat items ranging from the first edition of NewtonâÂÂs Principia through to horse drawncarriages and even Daleks do not deteriorate. Normally this uses energy intensive air conditioningsystems.

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The three-storey archival store that the Science Museum built in 2012 using a hemp-lime envelopewas 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 whilesaving a huge amount of energy.

Improved bio-based materials can also passively improve the internal air quality of buildings byinteracting with airborne pollutants, removing them from the building. The new HIVE building

 Ã¢Â a ã1m project funded by the Engineering and Physical Sciences Research Council Ã¢Â has been designed as a platform for research projects into this kind of sustainableconstruction. The HIVE has a purpose-built flood cell, which will also support research into creatingbuildings and building materials that are more flood-resilient â a valuable resource in thesetimes of climate change induced adverse weather conditions.

The Hivebuilding.ÃÂ Photograph: University of Bath

Industry and government must also embrace the opportunities presented by bio-based constructionmaterials to reduce emissions. Domestic housing is a key part of this. Good quality housing can bebuilt out of structural timber with a bio-based insulating envelope using straw; hemp-lime, or othersystems using wood fibre or other cellulose fibres.

With domestic housing high on the governmentâÂÂs agenda, it is time the construction industryrecognised the economic and environmental benefits of bio-based construction materials andbecame less reliant on depleting resources including oil and steel.

Dr Mike Lawrence is Director of the University of BathâÂÂs new research facility âÂÂtheàBuilding Research Park  Ã â aimed at reducing the carbon footprint of buildings.Follow the facility on twitterà@HiveBRP

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