Hempcrete is a bio-composite material made from hemp shiv (the woody core of the hemp plant) mixed with a lime-based binder and water. It is used as insulation infill within a timber frame. It is not load-bearing but provides excellent insulation, breathability, and carbon sequestration.

What is the standard hempcrete mix ratio?

The typical mix ratio is 2:1 by volume (hemp shiv to lime binder). This can be adjusted: more shiv for better insulation (wall fill), more binder for denser mixes (floor slabs). Water is added until the mix holds together when squeezed without dripping.

How long does hempcrete take to dry?

Hempcrete dries at approximately 1mm per day from each exposed face. A 300mm wall drying from both sides takes around 150 days to fully cure. Adequate ventilation and warm temperatures speed drying. Do not apply finishes until fully dry.

What U-value does hempcrete achieve?

Hempcrete has a thermal conductivity of approximately 0.06 W/mK. A 300mm hempcrete wall achieves a U-value of about 0.20 W/m2K, which meets current Building Regulations. For Passivhaus standards, 400-500mm thickness is needed.

Is hempcrete carbon negative?

Yes - hemp shiv sequesters approximately 1.8 kgCO2e per kg during growth. The lime binder also reabsorbs CO2 during carbonation. A typical hempcrete wall stores more CO2 than was emitted during manufacture, making it carbon negative over its lifecycle.

TradeCalculator

Hempcrete Calculator

Calculate hemp shiv, lime binder, and water quantities for hempcrete

Application

Area

How We Calculate This

Select the application type (wall, roof, floor, render) to set the default thickness. Enter the area to be covered. The calculator determines the total volume, then splits the mass between hemp shiv and lime binder using the specified ratio. Water quantity is estimated from the binder mass. Drying time is calculated from the wall thickness, and the U-value and carbon sequestration are computed.

Frequently Asked Questions

Related Calculators

Embodied Carbon Calculator

Calculate embodied carbon from material quantities using kg CO2e/kg lookup.

Recycled Aggregate Calculator

Compare recycled vs virgin aggregate with density adjustment and cost saving.

Green Roof Calculator

Calculate green roof substrate depth, drainage board, filter fleece and weight per m².

Rainwater Harvesting Tank Calculator

Size rainwater harvesting tank from roof area, rainfall and daily demand.

Passivhaus Metrics Calculator

Check Passivhaus metrics for space heating, airtightness and primary energy targets.

Last updated: March 2026

All calculations are estimates. Verify with your supplier.