How to Use Hempcrete for Sustainable Construction

How to Use Hempcrete for Sustainable Construction

I’ve been interested in sustainable construction methods for some time now. As our climate changes, it’s becoming increasingly important to build in an eco-friendly way. One material that shows a lot of promise is hempcrete.

What is Hempcrete?

Hempcrete is a bio-composite building material made from the woody core of the hemp plant mixed with a lime-based binder. The hemp core, called shiv, is blended with a lime-based binder and water to create hempcrete.

Some key properties of hempcrete include:

  • Sustainable – Hemp is a renewable resource that can be grown quickly and efficiently. The lime binder absorbs CO2 as it cures, making hempcrete carbon-negative.

  • Breathable – Hempcrete is porous, allowing moisture to pass through while regulating humidity. This helps prevent mold and mildew.

  • Insulating – The porous structure provides excellent thermal insulation, reducing energy costs.

  • Fire-resistant – Hempcrete forms a protective char layer when exposed to fire, preventing flames from spreading.

  • Pest-resistant – Hempcrete doesn’t provide food or habitat for pests like rodents.

  • Durable – Hempcrete structures can last for centuries with proper maintenance.

With these beneficial properties, it’s no wonder hempcrete is gaining popularity as a sustainable building material.

How is Hempcrete Used in Construction?

There are a few primary ways hempcrete can be incorporated into buildings:

Walls

Hempcrete makes an excellent insulated wall system. It can be cast into forms around a timber frame or reinforced with a lattice structure. Hempcrete walls provide thermal mass, allowing buildings to hold heat in winter and stay cool in summer.

Flooring

Hempcrete’s acoustic dampening properties make it useful for flooring systems. It can absorb sound rather than transmitting noise to rooms below. Hempcrete floor panels can be cast and then lifted into place during construction.

Roof Insulation

When used as a roof insulation, hempcrete enhances energy efficiency. It’s lightweight, so can be applied over roof rafters without overloading the structure. Hempcrete is moisture-resistant, protecting roofs from condensation issues.

Interior/Exterior Plaster

As a plaster or render, hempcrete provides passive humidity control along with thermal benefits. It can regulate indoor air quality when used on interior walls. Exterior hempcrete plaster helps balance moisture levels to protect the building envelope.

Key Steps for Constructing with Hempcrete

If you’re interested in using hempcrete for a building project, here are the main steps involved:

1. Design Structure and Formwork

  • First, design the structural elements of the building – timber framing, foundation, roof system, etc.

  • Determine where hempcrete will be applied and design proper formwork. Forms contain the hempcrete until it cures.

2. Source Materials

  • Obtain hemp shiv from a supplier selling it specifically for hempcrete use.

  • Choose a binder like lime, cement, or a lime-cement blend. Natural hydraulic lime works well.

  • Obtain necessary tools – spray equipment, tampers, formwork.

3. Prepare the Hempcrete Mix

  • Blend hemp shiv with the binder at the proper ratio, typically 2-3 parts hemp to 1 part binder.

  • Add water gradually until the ideal consistency is reached. The mix should be moist but not soggy.

4. Pour or Spray Hempcrete into Forms

  • Lift hempcrete into wall forms via cranes or conveyors.

  • Alternately, use spraying equipment to apply hempcrete. Maintain consistent depth and density.

  • Tamp regularly to compact the material and avoid voids.

5. Monitor Curing

  • Allow hempcrete to cure within the forms, typically 4-6 weeks.

  • Monitor moisture levels and keep surfaces protected.

  • Once cured, remove forms carefully to avoid crumbling.

Cost Comparison to Traditional Building Materials

While the material costs for hempcrete are higher than conventional concrete or stud-framed walls, the energy savings can provide a quick payback. Here’s a rough cost comparison:

  • Hempcrete walls: $15-20 per square foot installed

  • Standard concrete walls: $4-8 per square foot

  • Wood-framed walls: $12-18 per square foot

Hempcrete becomes cost-competitive when the full lifecycle is considered. The energy efficiency and longevity provide good value for money over the life of the building.

Key Benefits of Building with Hempcrete

To summarize, here are some of the main benefits hempcrete offers as a sustainable building material:

  • Energy efficient – Hempcrete walls can reduce heating and cooling costs by up to 50-70%. This saves money and reduces environmental impact long-term.

  • Carbon negative – Hemp absorbs CO2 as it grows. The lime binder also absorbs CO2 during curing. Hempcrete effectively sequesters carbon.

  • Healthy interior climate – Hempcrete regulates humidity and absorbs pollutants. This creates a healthier indoor environment.

  • Durability – Hempcrete maintains its structural integrity and insulating value over centuries. This enhances building lifespan.

  • Fire resistance – Unlike timber framing, hempcrete won’t combust or release toxic smoke. It slows fire spread.

  • Sustainability – Hempcrete represents a renewable, low-impact building method. It reduces ecological harm compared to concrete and steel.

With proper design and installation, hempcrete is an optimal choice for sustainable construction. Its environmental benefits and performance features make it a valuable green building solution moving forward.