As proud members of the Embodied Carbon Network and the associated renewable materials taskforce we were asked to contribute to the 2030 Palette program for Architecture 2030. The following is what we had to offer.
A wool fiber is much different than a synthetic one. It is rapidly renewable and sustainable, and dynamic in its construct. At the end of an extended useful life it can be composted, thus avoiding landfill.
Sheep wool’s inherent characteristics have evolved in nature over 1000s of years to become the perfect insulator. Notably a wool fiber manages moisture – absorbing and desorbing against ~65% rh. 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.
The amino acids in wool are also able to bond with harmful chemicals such as formaldehyde, nitrogen oxide and sulphur dioxide. We know the most about formaldehyde. The bond is both chemical and physical. Chemisorption is a short 80% and irreversible, the physical bond (physisorption) is the balance and only reversible at extreme heat and moisture levels (ie saturation).
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.
Sound attenuation is another inherent characteristic that equates to an outperformer as insulation. Wool has a noise reduction coefficient of 0.90 at a minimum, up to 1.15.
From the perspective of carbon, the wool trade is known to sequester some 525,000 tons of atmosphere derived carbon per annum. These figures would of course go up were the sheep population to experience any type of reversion to mean population levels.
On the insulation production side of things wool may stand out even further than the alternatives. Fibers are made in nature, not a factory. Most (wool) products on the market are devoid of glues and bonding agents which dispels two hugely energy dependent requirements for synthetic fibers: fiber creation and the subsequent melting into finished product.
Finally, as an insulator wool will either meet or exceed rvalue per inch measures of most other mediums. Batts are at industry standard measuring r3.6 per inch and some loose fill products outperform at roughly r4.3 per inch.
Wool insulation is similar to other forms of insulation when it comes to installation. It is equally useful in new construction as it is for a retrofit. Batts are installed like other forms of insulation. Blow-in is also easily installed using slightly modified, readily available, machinery. Protective clothing is not required for installing wool insulation.
- Wool insulation can be sourced in both batt and blow-in forms.
- Wool inherently manages moisture, while improving indoor air quality – by absorbing harmful chemicals; kills off airborne sound and is naturally self-extinguishing.
- Wool is a keratin and therefore will not support the growth of mold.
- The production of wool fibers sequesters some 525,000 tons of atmosphere derived carbon.
- 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.
Sheep’s wool insulation should not have a synthetic mix. Fibers of a lower quality may not only negatively affect performance but may also negate some of wool’s inherent advantages eg moisture management and flame retardancy.
Processing will vary relative to fiber dynamics. Coarse wool, absent medullated fibers, is best to maintain a spongy, compression resistant consistency post-application.
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.
Challenges / Questions / Unknowns:
Sheep’s wool is available in the US though it comprises an insignificant amount of the annual yield ie ~1%. Logistics for moving wool as raw material are, however, quite favorable. For example, some 44,000 pounds can be moved in a 20 ft. container – equal to roughly 3% logistics costs. Manufacturing of finished goods can and does happen in the US. A shift to raw material sourcing here would require larger sheep populations, more consistent shearing operations and better scouring options.
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 a low net embodied energy relative to production, wool fibers sequester carbon on their own. There are products that fully conform to Class A of the building code and are readily available for commercial and residential projects of all shapes and sizes.
Insulation values are as follows:
|Thermal Conductivity K Value
|Thermal Conductivity K Value
|Thermal Resistance R Value
|Thermal Resistance R Value
|Thermal Resistance per inch R/in
|Btu-in/hr * Ft2 * F
|W / (m*k)
|Hr * ft2 * F/Btu
|(m2 * K)/W
|Hr * ft2 * F/Btu/in
|Hr * ft2 * F / Btu / in
Source: Havelock Wool Insulation Third Party Testing Data
Pure organic carbon makes up 50% of the weight of wool, higher than cotton (40%) or wood pulp–derived regenerated cellulosic such as viscose (24%).
Converted into CO2 equivalents (CO2-e), 1 kg of clean wool equates to 1.8 kilograms of CO2-e stored in a durable, wearable form.
Extending this concept, the global wool clip represents around 1.05 million tons of clean wool which equals to 1.9 million tons of CO2-e, or 525,000 T of pure, atmosphere-derived carbon.
Wool is readily biodegradable, unlike most synthetic fibers, and wool clothing and processing wastes are routinely recycled into other durable forms of textile (woollen-spun knitwear, insulation, geotextiles).
The carbon in wool is derived from carbon from the pasture – and thus sequestered from the current atmosphere.
1. Wool is produced in extensive pasture systems, where the diet is dominated by grasses and herbs. These plants convert CO2 from the atmosphere into organic compounds using light energy – as part of the photosynthesis process which underpins most life on earth.
2. Thus, when you purchase wool insulation, you are purchasing carbon sequestered from the atmosphere 1 – 2 years earlier. By comparison, the carbon in the major synthetic fibers such as polyester or acrylic is extracted from fossil fuels (de-sequestering carbon originally stored millions of years ago).
Source: Green Wool Facts: The Wool Industry & The Environment | International Wool Textile Organization, Rue de l’Industrie 4, Brussels, B-1000, Belgium
Carbon Effect of Wool Insulation in a Wall?
Assume: 4’ x 8’ wall section. R value target: 28.
Kilograms of wool needed: 9kg (19.8lbs)
Carbon effect: -16.2 kgCO2e