Department of Architecture and Civil Engineering

Developing hemp-lime low-carbon construction for mainstream uptake through innovation and optimisation

At a glance

Funding body: DEFRA
Principal investigator: Pete Walker
Co-investigator: Kevin Paine and Enrico Fodde
Researcher: Mike Lawrence
Industry partners: Lhoist UK, Lime Technology Ltd, Hanson, Wates Group, BRE Ltd, Feilden Clegg Bradley Studios, Hemp Technology Ltd, NNFCC
Dates: 2009-2012

Abstract

Hemp-lime is a lightweight composite material that combines renewable plant based aggregates (fast growing hemp shiv) with a lime based binder to offer a potential step change in the environmental performance of construction materials, potentially leading to ‘better than zero carbon buildings’. This performance is possible as a result of the carbon sequestrated and stored within the hemp during its growth, the comparatively low carbon footprint of lime following its carbonation, and the very efficient thermal performance possible during the life cycle of the building. It requires just one-hectare of arable land to grow, in just four months, sufficient hemp for one typical three-bed roomed UK house.

Use of renewable crop materials in construction, such as hemp, offers economic and social benefits to rural economies through new agricultural markets for farmers and associated industries. Spray application of hemp-lime is a recent innovation that increases the rate of application and potential for wider adoption by mainstream construction, but also offers opportunities for significant innovation with both material formulations and forms of wall construction.

Although there have been a small number of successful buildings in the UK in recent years, significant barriers to wider uptake of hemp-lime still exist. These barriers include: lack of confidence in the use and performance of a highly novel plant based material; lack of design guidance (including construction details and specification); and, limited understanding of hygrothermal material behaviour. Our research project seeks to directly address the main technical barriers to the uptake of hemp-lime construction.

The overall aim of the project is to generate and capture robust scientific and engineering knowledge of hemp-lime composite materials and construction performance to provide conditions for wider market uptake. The research project will conduct experimental research to characterise the physical and mechanical performance of spray applied hemp-lime materials.

The research will also seek to develop novel material mixes and layered wall construction methods, made possible by spray application, to optimise carbon capture and material performance in-service. By constructing and monitoring the performance of an experimental building, combined with broader studies of other buildings, the project aims to capture robust data on the novel hygrothermal performance of hemp-lime. These data will be used to develop and validate environmental modelling techniques for hemp-lime construction, providing much needed design guidance.

Finally, the project will support and promote hemp-lime construction through a range of dissemination and support exercises.