Tag: non-toxic

The Ultimate Guide to Hempcrete: An Eco-Friendly Alternative to Concrete

The interior of a modern hemp home in Israel.

As well as a superfood, bio-plastic and incredible skincare ingredient, another one of hemp’s many uses is as a building material. Far from a new concept, hemp’s use as a concrete-like building material dates back to Roman times. Strong, durable, flexible, breathable, mould-proof and fire resistant, hempcrete appears to be in a renaissance with builders and botanists working to renew the market.

Hempcrete can play an important part in the sustainability movement to help produce eco-friendly homes that not only have all these amazing properties but look pretty cool too!

What is Hempcrete?

A prefab hempcrete block.
A prefabbed hempcrete block. Image by DuChanvre

Hempcrete is a bio-composite made of the inner woody core of the hemp plant mixed with a lime-based binder and water. Hemp core or “shiv” is the fibrous, woody core of those stalks that are chopped up into small chips. Hemp shiv has a high silica content which allows it to bind well with lime, this is unique to hemp among all natural fibres. The result of this powerful combination is a lightweight, cement-like material weighing about 8x lighter than concrete.

Hempcrete is not used as a structural element in building, instead it is used as an insulating infill between/around the structural framing (most commonly wood). It can be used for interior and exterior insulation of existing buildings, as well as for the filling of wooden frames in new constructions.

Hempcrete differs from typical insulation materials as it forms the walls and insulation in one piece. In terms of a finish, internal walls are typically plastered with a clay or lime finish, and external walls with a lime finish.

How is Hempcrete made?

Hemp shiv, water and lime binder are mixed in a concrete mixer for approximately 2 minutes. Once sufficiently mixed the material is packed by hand around the structural framing into temporary wooden or plastic shuttering.

Hemp shiv, the ground up core of the hemp plants stem.
Hemp hurd or ‘shiv’ is combined with lime binder and water to produce hempcrete.

Over time the chemical reactions between the water, lime and hemp petrify the hemp and turn the lime back into stone. The material is finished on the outside with a hard render coating about 20mm thick to protect it with a final coloured topcoat finish added. The end result appears like any stucco finished building. The inside can be left natural or finished with lime plaster for a traditional, natural look.

Advantages of Hempcrete

There are many clear advantages to using Hempcrete, these include:

Acts as an insulator and moisture and humidity regulator

Due to its porous structure hempcrete acts as both an insulator and moisture regulator, this helping to control condensation and air quality by allowing water vapour to pass through.

It is also hygroscopic, this means that it absorbs moisture into the material during times of high relative humidity in the air, releasing it again when the relative humidity drops. This is very important in a ‘healthy home’, as it discourages the formation of mould spores which can be harmful to human health.

Natural and Non-Toxic

Hempcrete is completely natural and free from synthetic, fossil fuel based materials. Because it is naturally pest-resistant and fire-retardant, toxic chemicals typically added to help performance in these areas are not required. This makes for hempcrete homes being extremely healthy living environments, especially for people with allergys.

Ideal for most climates

An interior hemp wall finished with a lime based top coat.
A hempcrete wall with a hard-render finish. Image by DuChanvre

Hempcrete has amazing thermal qualities, reducing the requirement for heating and cooling during the lifetime of the building (providing incredible electricity savings). It provides insulation due to pockets of air trapped within the material; both in the hemp shiv itself, and the spaces between particles of hemp shiv.

The thermal conductivity of hempcrete varies due to the thickness. Walls are typically 300-400mm thick, providing 0.2-0.15 W/m2K (thermal conductivity measurement).

As well as having excellent thermal conductivity, hempcrete also provides great thermal mass (the ability of a material to absorb and store heat energy). It is able to store heat in the material itself unlike typical lightweight insulations, which only keep heat in a building due to the air trapped inside the material.

These amazing qualities allow hempcrete to provide natural ventilation of the building, as well as buffering natural changes in outdoor temperature by slowly releasing heat stored within the material, how cool is that!

Hemp can be harvested in perpetuity

The hemp plant is an extremely tenacious plant that has adapted to grow on every continent except Antarctica. From seed to harvest (10-15ft tall), hemp plants take just 3-4 months to grow. Commonly referred to as “weed” for a reason, the hemp plant grows incredibly fast and require fewer pesticides, fertilisers and water than wood.

Because hemp is grown so easily and fast (especially compared to wood that takes many years to grow), it makes for an excellent sustainable building material.

Naturally Fire-Retardant and Pest-Resistant

Hempcrete is naturally both fire-retardant and pest-resistant. Lime is completely unappealing to pests/termites (they will not eat it) and hydraulic lime in your hempcrete mix will render the encapsulated wood fire-proof and not create a toxic black smoke. As mentioned above, these unique characteristics mean that no harmful/toxic chemicals need to be added to provide these important properties.

In 2009, a British Fire test showed that a 10 x 10 x 12-inch wall could withstand temperatures of 1,800 degrees Celcius while subjecting to a vertical load of 13,500 kilograms. The wall met requirements for integrity, insulation and load bearing capacity for 73 minutes.

Easy and safe to work with on construction site

When produced and installed correctly, hempcrete is extremely easy and safe to work with.

  • Besides the mixer, no power tools are required. This produces a quiet worksite with no cables to worry about.
  • Instead of your typical heavy, caustic, toxic concrete, hempcrete provides a light, non-toxic material that is easy to move around the site.
The exterior of a modern hempcrete home in Israel.
A modern hemp home in Israel.

Hempcrete is Carbon-Negative

Hemp plants are experts at absorbing CO2 from the atmosphere, this helping them to grow quickly and outpace competing plants. A house built using hempcrete will reduce the CO2 debts of the house on multiple levels. This includes reduction in waste, the low embodied energy of the materials required, thermal performance and air-tight construction.

As hempcrete dries, it absorbs the carbon dioxide produced by the occupants of the house and grows harder, essentially turning to stone. Not only does this produce a stronger building, but it makes it into a carbon-negative building material by leaving less CO2 in the atmosphere than is produced by building with it. This is an extremely important factor as we work towards a more sustainable and eco-friendly future.

Estimates vary, but it is thought that ~165kg of CO2 is sequestered (taken away) from the atmosphere for every 1m3 of hempcrete produced.

Some Disadvantages to using Hempcrete

Limited experienced businesses offering the service

As a relatively new material in terms of popularity/interest, there are not many experienced hempcrete builders or companies. It can be difficult to work with until some of the key techniques and concepts are understood. Because of this, it is important to use builders who have these key concepts mastered and have prior experience using the material professionally.

Additionally, being somewhat of a fringe material few architects have experience and the knowledge of how to incorporate hempcrete detail into drawings/concepts correctly.

May not be easily available in your area

Being a relatively unknown building material, there are few experienced companies offering hempcrete construction as a service. Depending on your location, it may be difficult to find a local company to help you with a hempcrete build, i.e you may be required to find a company out of town/state.

Fun facts about Hempcrete

  • Buildings ten stories high have been built in Europe using hempcrete.
  • Theoretically, 165 kg of carbon can be absorbed and locked up by 1m3 of hempcrete wall during manufacture.
  • It is a low-density material and resistant to crack under movement thus making it highly suitable for use in earthquake-prone areas.

TL:DR (The too long didn’t read summary on Hempcrete)

  1. Is a concrete-like material used in the construction of eco-friendly homes.
  2. Combines hemp shiv, lime and water to create a concrete-like material that is strong, durable, flexible, breathable, mould-proof and fire resistant.
  3. Hempcrete homes are carbon-negative, meaning they take more CO2 out of the atmosphere than put in during both construction and the lifetime of the building.
  4. As well as having excellent thermal conductivity, hempcrete also provides great thermal mass (the ability of a material to absorb and store heat energy).
  5. Limited hempcrete service providers may make it hard to build using hempcrete in your area.

Videos

Gran Designs Host Kevin McCloud on Hempcrete

Building with Hemp – An Incredible Natural Insulation & Sustainable Material

References

  1. Hempcrete FAQ by UK Hempcrete
  2. Thermal Properties of Hempcrete – A Case Study by Jere Komsi
  3. Structural benefits of hempcrete infill in timber stud walls
  4. Hempcrete – an environmentally friendly material?
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