The Australian Hemp Masonry Company


AHMC Hemp Insulation



A Hemp lime mixture that is even lighter than the walling material produces a very effective roofing insulation material. Using hemp lime as the roofing insulation material and joining the roofing insulation to the walls creates a very effective thermal envelope, maximising operational energy efficiency and reducing energy costs.

Synthetic insulation materials such as polystyrene or polyurethane should be avoided in hemp lime construction. They will compromise the breathability of the hemp lime walls. It is also normally not advisable to place an insulation quilt or batt directly in contact with hemp masonry, as moisture when the material is initially cast, can migrate to the insulation material.

R Value

  •  Depending on the climate zone 150mm – r3 to 250mm – r5 of hemp lime insulation is recommended for roofing in Australia.
  • In really cold climates up to 300mm of roofing insulation is used.


  • The roofing engineering must be designed to support the wet weight (35% Heavier than when dry) of the insulation material.
  • Wet weight of the insulation material is 218Kg per cubic metre
  • Dry weight is 143kgs per cubic metre.

Hemp lime walling materials are tamped, however roofing insulation is raked into place with minimal compaction. It is important to take care that all gaps are filled. Some contact is needed between the small pieces of Binder covered hemp hurd to form an insulation wafer.

Where the roofing insulation is installed from outside, temporary planks or battens should be attached to give the installer additional security. All safety precautions associated with working at heights must be observed. The material should be protected from rain and it’s preferable for it to cure out of direct harsh sunlight in summer.  It should be covered as soon as possible. 


The same lighter hemp lime formulation that is using in roofing insulation can also be used as subfloor insulation and as insulation for suspended floors. The material has high vapour permeability, high elasticity and flexibility and it is an excellent insulator.

A minimum of 100mm – 150mm of hemp insulation is recommended. As with walls, all electrical conduits and plumbing need to be fixed before the hemp lime insulation is installed from above.

The formwork or cladding which is usually either 12mm magnesium oxide board or a composite wood sheet is attached under the floor joists and this must be supported appropriately when the insulation has been freshly installed and is still wet and approximately 35% heavier than when dry.