The pros and cons of sheep's wool insulation for your home

So sustainable, so soft but is it for &#;ewe&#;?

Whether your goal is to reduce your carbon footprint or minimize heating expenses, insulating our homes is undeniably essential. The challenge lies in determining which insulation material is superior and understanding the advantages of choosing certain types over others.

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The phrase &#;natural insulation&#; encompasses materials like sheep's wool, flex, and hemp, along with products that incorporate a significant proportion of recycled materials such as cotton, paper pulp, or wood pulp.

Recently, the construction sector has predominantly relied on oil-derived insulation materials. Synthetic options like polyurethane, phenolic foam, and polystyrene insulation boards tend to outperform natural insulation in terms of thermal resistance. Practically speaking, this suggests that natural materials might necessitate greater thickness to achieve the same level of insulation in a building. So, what makes sheep's wool insulation a viable choice?

Perhaps the answer lies in the fact that insulation extends beyond just thermal resistance. Sheep's wool insulation boasts additional compelling benefits as well.

What is sheep's wool insulation?

Sheep have thrived in cold winters for millennia, thanks to their plush warm fleeces. Regardless of how severe the conditions, the wool on their backs keeps them insulated and dry. The crimped structure of wool fibers creates millions of tiny air pockets that trap air and hinder heat transfer, rendering wool a natural insulator that maintains warmth in winter and coolness in summer.

Although sheep are no longer farmed solely for their wool, they still require annual shearing to ensure their health. Wool insulation is crafted from sheep wool fibers that are either mechanically bonded or glued together to create insulating batts and rolls. This insulation can be tailored to size and installed similarly to other kinds of insulation. While some manufacturers offer 100% sheep's wool insulation, others provide insulation that is wool-rich (75% wool) combined with recycled polyester.

PROS

Natural, renewable and sustainable.

Sheep's wool ranks among the top insulating materials in terms of sustainability. Sheep are sheared annually, and their wool continuously grows back. As a raw material, wool is abundant, renewable, and predominantly locally sourced in Britain. It has a long lifespan and can be composted at the end of its life. Unlike oil-based insulation, it contains no synthetic fibers.

With increasing awareness of plastic pollution, the impact of plastic materials on the environment has come under scrutiny. Despite a rise in recycled plastic insulation, most still ends up in landfill.

Low embodied carbon

This metric assesses the balance between global warming emissions associated with material production and those preserved by the insulation itself. It also weighs the gases emitted through fossil fuel utilization, energy reserve during raw material extraction, and the manufacturing process.

For instance, producing plastic insulation demands oil, chemicals, and substantial energy. Conversely, rock wool manufacturing involves melting volcanic rocks in a furnace and spinning them into fibers.

Sheep's wool consumes considerably less energy during production than synthetic insulating materials. Sheep's wool scores 6 MJ/kg in embodied carbon, compared to 101 for polyurethane foam and 26 for glass mineral wool, as per analysis by GreenSpec.

Protection against moisture

Manufacturers assert that wool is among the few insulation materials that exhibit breathability, naturally absorbing and releasing moisture.

The outer layer of wool is hydrophobic (water-resistant), while its inner cortex is hydrophilic (water-absorbing). This permits the cortex to absorb moisture without dampening the wool itself. Consequently, it helps safeguard adjacent timber against moisture and inhibit mold survival.

Unlike numerous other materials, wool can hold up to 30% of its weight in moisture before its thermal properties are affected. This quality makes it suitable for damp climates, such as the UK.

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Help control temperature

When wool fibers absorb moisture, they release it back into the air as heat, elevating the surrounding temperature. Manufacturers claim that wool's inherent capacity to absorb moisture in humid environments and subsequently release it in dry conditions can help maintain stable indoor temperatures, enhancing comfort.

Ease of installation

Sheep's wool is user-friendly and simple to install. Unlike many synthetic insulations, it generally does not irritate the skin (unless there's a wool allergy), eyes, or lungs. This is a stark contrast to glass wool or rock wool insulation, where protective gear like full-face masks, goggles, and gloves are necessary during handling.

Sheep's wool insulation is also easy to cut and shape for a precise fit. Manufacturers claim it can be utilized throughout your home for thermal and acoustic insulation, including attics, roofs, walls, floors, ceilings, piping, ducting, and water tanks.

Specific heat capacity

This denotes the energy required to raise the material's temperature by one degree. High specific heat capacity signifies that a good insulator can stabilize temperature changes, absorbing heat over time before it truly increases. According to GreenSpec’s analysis, sheep's wool insulation outperforms plastic and mineral wool, scoring well on specific heat capacity metrics. For example, it measures J/Kg.K for sheep's wool versus less for glass mineral wool and expanded polystyrene (EPS). This means sheep's wool performs better in absorbing heat during hot summer months.

Flame resistant

Sheep's wool is naturally resistant to flames. Due to insufficient oxygen in the air, wool merely chars rather than catches fire. In case of a fire, it will not serve as fuel and emit no toxic gases.

Like all insulation materials, sheep's wool must pass fire safety tests to meet regulatory standards. Products are subjected to Euro Class C or British Standards, such as BS 476 or BS . Necessary fire retardants based on inorganic mineral materials are added as needed.

Soundproof

Another advantage is the acoustic properties of natural fiber insulation. Sheep's wool can significantly dampen sound transmission within a building. Thanks to its high density, irregular shape, and soft fibrous quality, it provides remarkable soundproofing capabilities, even exceeding some of the best mineral fiber insulations. This makes it ideal for bedrooms, home offices, and music rooms.

CONS

Lower thermal efficiency

Thermal performance is vital when evaluating insulation materials. Thermal resistance (R) gauges the heat loss through a specific thickness of a material expressed in resistance per unit area (m2K/W). The higher this figure, the better the insulation performance.

Per GreenSpec, plastic insulation typically boasts nearly double the thermal resistance of sheep's wool insulation—R values of 5 per 100mm m2K/W for phenolic foam and 4.5 for polyurethane foam, compared to 2.5 per 100mm m2K/W for sheep's wool. Additionally, rock mineral wool and glass mineral wool carry R values approximately 0.3 points higher, indicating wool’s thermal performance isn’t the most competitive overall.

Chemical treatments

One significant downside of wool is its susceptibility to pests, particularly moths. To combat this, raw wool must undergo chemical treatment to prevent insect infestations. For example, manufacturers like Thermafleece treat the wool with borax for pest protection.

Alternatively, SheepWool utilizes a plasma-ion treatment, known as &#;Ionic Protect&#;, that modifies wool fibers on a molecular level to provide lasting insect resistance without biocidal agents.

Expensive

Compared to some other insulating options, sheep’s wool can be pricier. Expect to pay around £18 to £25/m2 at 100mm thick for 100% wool insulation, while a blend of wool and polyester generally comes out at a lower price point.

This contrasts with mineral or rock wool insulation, which costs around £13 per metre. Spray foam insulation tends to be costlier, with prices starting at around £27 per metre. (Price data is accurate as of February).

Sheep’s wool emerges as a natural, renewable, and breathable insulator that offers effective soundproofing and fire-resistant properties. It helps create a balance of temperature and humidity within your living space. Although there are numerous advantages, it may not be the ideal choice for everyone. Other synthetic materials may provide superior thermal performance and lower costs, albeit at a higher environmental cost.

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