Low Energy House » Sheep's Wool - Renewable Insulation

Sheep's wool is a very efficient insulation material and its low conductivity compares favourably with other fibrous insulants. It is a renewable source material with low embodied energy and can be recycled

Production of Sheep's Wool Insulation

Natural wool is collected from sheep that have not been dipped. It is washed several times to remove the lanolin then mixed with polyester which helps to keep its shape. Wool batts generally contain 85 per cent wool mixed with 15 per cent polyester. Sheep's wool is a natural fibre derived from a fully renewable resource. 

The cleaning, air laying and thermal bonding processing during the manufacture consumes minimal energy.  It uses only 14 per cent of the energy used to manufacture glass fibre insulation.

Sheep's Wool - Thermal Efficiency

Sheep's wool is hygroscopic and will therefore absorb and release water vapour without compromising its thermal efficiency. In cold weather, sheeps wool absorbs heat from moisture in the air which enables it to reduce heat loss from the building. In warm weather, the release of moisture has a cooling effect on the fibre which reduces the flow of heat into the building.

Availability of Sheep's Wool

Sheep's wool is generally available in packs of batts either 400mm or 600mm wide and in three thicknesses of 50mm, 75mm and 100mm. Sheep's wool is suitable for the thermal insulation of lofts, rafters, timber framed walls and timber suspended ground floors.

Physical Qualities of Sheep's Wool

Sheep's wool can be cut easily with a sharp knife or shears and requires no protective equipment to install. The quilt adapts to the shape of rafters, joists and studs to provide a permanently tight fit. When properly installed, it will retain its low density and thermal performance and have a life expectancy in excess of fifty years.

Sheep's wool is potentially susceptible to rodents which may use it as a nesting material but the batts are treated with an insecticide to protect moth or beetle attack.

Fire Safety

Wool has a higher resistance to fire than cellulose and cellular plastic insulants. It melts when it comes into contact with an ignition source but should extinguish itself. It is treated with a non-hazardous fire proofing agent to improve its fire resistance, ignitability and surface spread of flame.

Thermal Performance of Sheep's Wool

Sheep's wool has insulating properties which are equivalent to mineral fibre insulation. A total thickness of 250mm, of the insulation material, when fitted in a loft floor will give a U-value of 0.16 w/m²k .

The low thermal conductivity of sheep's wool batts is 0.039 W/m K at 10 degrees C which is similar to that of other fibrous insulants.

In the UK, when comparing the thermal values of insulating materials, it is important to remember that the best performing material is the one with the lowest thermal conductivity value