Havelock Wool insulated a 17,000 square-foot residence in Newport Beach, CA, using their wool batt product.
Photo courtesy of Havelock Wool
Carbon Impact of Sheep’s Wool
Wool insulation is made from sheep’s wool fibers. Wool is an effective thermal and acoustic insulation and is available in both batt and blow-in forms. Wool inherently manages moisture, improves indoor air quality by absorbing harmful chemicals, is sound absorbing, and is naturally fire resistant. Wool is a keratin and therefore will not support the growth of mold. It is important to distinguish natural sheep’s wool from mineral wool or rock wool, which are actually made from rock, blast furnace slag, or other raw materials which are then melted and sun into fibers.
Wool fibers sequester atmospheric carbon. Carbon makes up 50% of the weight of wool (compared to 40% for cotton and 24% for cellulose). This carbon comes from the grasses and other plants that wool sheep eat. Most products available conform to Class A of the building code. Products are readily available and increasingly being used in projects of all sizes across the US, Canada, the EU and Australasia.
Statistics
- Carbon makes up 50% of the weight of wool, higher than cotton (40%) or wood pulp-derived cellulose (24%)
- 1 kg of clean wool equates to 1.8 kg of CO2 stored
Carbon Smart Attributes
Wool sequesters carbon and other chemicals
Much of the carbon in wool comes from the plants that wool sheep eat, though the amino acids in wool are also able to bond with CO2 and other harmful chemicals such as formaldehyde, nitrogen oxide and sulphur dioxide.
A wool fiber is much different than a synthetic fiber
Wool is a natural, rapidly renewable material, whereas synthetic fibers are often chemical derived and then spun into a fiber. At the end useful life, wool can be re-used and/or recycled due to its durability, or composted, thus avoiding landfill. Most wool products on the market are devoid of glues and bonding agents, whereas synthetic fibers require two additional carbon-intensive processes: fiber creation and the subsequent melting into finished product.
Material Attributes
Wool has competitive thermal performance
Sheep wool meets or exceeds the r-value per inch measures of most other mediums. Wool batts measure r3.6 per inch and some loose fill products are measured at roughly r4.3 per inch.
Durability – moisture performance
Wool fibers manages moisture – absorbing and desorbing against ~65% relative humidity. The fiber itself has a hydrophobic (water repelling) exterior and a hydrophilic (water loving) interior. The five follicles within the fiber mean it can hold up to a third of its weight in moisture and still feel dry to the touch. This allows the insulation layer to go on insulating during and after inevitable bouts with moisture. Also, wool is a keratin and therefore does not support the growth of mold.
Durability – fire performance
Wool is self-extinguishing. It has a high nitrogen content (~14%) and therefore will not support a flame until 1100F. This means dangerous flame retardants are not necessary in wool insulation though it still conforms to Class A of the building code.
Wool is a natural sound absorber
Wool insulation is an excellent sound absorber, with a noise reduction coefficient of 0.90 to 1.15.
Design & Construction Guidance
Use coarse wool without synthetic fibers
Adding synthetic fibers or bonding agents to natural sheeps wool may negatively affect performance by reducing the wool’s naturally spongy, compression resistant consistency post-application. Additionally, adding synthetic fibers or chemicals may also negate some of wool’s inherent advantages (e.g. moisture management and flame retardancy). Use natural sheeps wool without synthetic fibers or chemical bonders.
Ensure proper density
Density measures can affect sound deadening and insulation values. Installation should be per the manufacturers specification which is based on a simple calculation relative to third party testing results.
Acknowledged Challenges, Questions & Unknowns
Sheep’s wool is available in the US though it comprises an insignificant amount of the annual yield ( ~1%).
Sheep’s wool as insulation is catching on in other parts of the world such as Germany, Scandinavia, Turkey, Mongolia, Eastern Europe and North America – in addition to those places where it has been used for some time: the UK, Australia and New Zealand.
Sheep’s wool insulation employs a light manufacturing process. In addition to low embodied carbon for production, wool fibers sequester carbon on their own. There are products that fully adhere to the Class A requirements of the building code and are readily available for commercial and residential projects of all shapes and sizes.
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