Hempcrete
Contents |
[edit] Introduction
Hempcrete, also known as hemplime, is a bio-composite material that can be used in construction as an alternative to materials such as concrete and traditional insulation.
The basis of hempcrete is hemp, the balsa wood-like core (or ‘Shiv’) of a cannabis sativa plant. Hemp can be combined with lime and water to form hempcrete. The hemp has a high silica content, a unique property among natural fibres, which allows it to bind well with the lime. As a lightweight cementitious insulating material, it weighs only one-seventh to one-eighth that of concrete.
Hemp as a building material has been used across Europe for centuries, and as a modern building material, industrial hemp is now grown by certified commercial growers. The strain of plant grown for hempcrete contains 0.3% of THC, the ingredient in cannabis that provides its psychoactive nature. This is compared to the THC content found in hallucinogenic and medicinal varieties of between 5-10%.
While it is legally grown in Europe and Canada, growing hemp in America has been illegal for several decades. However, with the country’s gradual liberalisation of laws regarding the substance for medicinal and personal use, this may change.
[edit] Application
The material is mixed for 1-2 minutes before being applied, either into the wall cavities, or slip-forming with temporary timber or plastic shuttering. A hard render coating is generally applied as a finish on exterior surfaces with a thickness of around 20 mm. The interior can be left 'natural' or, for a traditional aesthetic, finished with lime plaster.
[edit] Properties
Hempcrete is very durable and has a number of other beneficial properties.
Similar to other natural plant products, carbon dioxide is absorbed from the atmosphere by hemp as it grows. During the curing process, as lime turns to limestone, the carbonation of the lime adds to this effect. As a result, hempcrete has a negative carbon footprint, with considerable potential for sustainable building.
It is able to naturally regulate a building’s humidity and temperature, which can reduce condensation and energy consumption, and improve thermal comfort for occupants. It provides natural insulation that is airtight, breathable and flexible. It is also toxin-free, impervious to mould and pests, and highly fire-resistant.
It is very suited to areas at risk of seismic activity since it is a low density material that is resistant to cracking under movement. The outer portion of the plant’s stalk can also provide fibres for building textiles.
However, hempcrete has a typical compressive strength of around 1 MPa, which is around 1/20 that of residential grade concrete, and has a density 15% that of concrete. This means that hempcrete walls must be used together with a load-bearing frame of another material.
[edit] Find out more
[edit] Related articles on Designing Buildings Wiki
- Blockwork.
- Cavity wall insulation.
- Cellular concrete.
- Composites.
- Concrete.
- Could the buildings of the future be made with bones and eggshells?
- Earth building.
- Floor insulation.
- Green building.
- Hemp lime construction: A guide to building with hemp lime composites.
- High alumina cement.
- K-Briq.
- Limecrete.
- Straw bale construction.
- Sustainability.
- Thermal insulation.
[edit] External resources
- American Lime Technology - What is hempcrete
Featured articles and news
A transformative shift in the design, construction and management of built assets.
Apprenticeship announcement by the Prime Minister
Welcomed but with call for more actionable detail.
Heat pump announcements, what homeowners need to know
An 'ultimate guide to heat pumps' from a heating company.
Construction contract awards reach 7.1bn in February
Their highest level in seven months.
The journey to sustainability in heritage
Research is the key to better understanding.
Heritage approaches to adaptation, mitigation and loss.
Bridging the gap between policy, finance and installation.
Development on brownfield land
Definition, background, policy and the latest consultation.
With the Design Framework for Building Services.
Retrofit of Buildings, a CIOB Technical Publication
Pertinent technical issues, measures and the roles involved.
ECA joins HSE campaign to support mental health
Working Minds’ five simple steps based on risk assessment.
Mental health in the construction industry
Mental health issues in brief with related articles.
Transitional arrangements, Building Control and the BSR.
For pre-October buildings with substantial progress by April.
Why quality counts in domestic ventilation systems
From products, to systems to the installation.
Empowering the Future with CIOB Academy
Lifelong learning, upscaling, and reskilling for the built environment.