Last Updated: Oct 20, 2021
The number of plastics, PVCs, polyurethanes, and other petrochemical inputs common in dozens of household items shows how hard it truly is to reduce our addiction to fossil fuels. For example, millions of homes worldwide rely on spray foam insulation, a chemical product created by combining an isocyanate and polyol resin. This chemical insulation product, when properly installed, can certainly improve the energy efficiency and thermal performance of a home. That is part of why spray foam insulation grew from 3 percent of households in 2008 to 11 percent of the insulation market in 2012. Despite its energy efficiency and cost-effectiveness benefits, spray foam is still very much fossil fuel-based.
A zero-emission, climate-friendly future civilization will not rely on products that stem from fossil fuel extraction. Transitioning to a bio-economy, then, is one of our most pressing tasks and challenges. The European Commission defines the bio-economy as "the production of renewable biological resources and converting these resources and waste streams into value-added products, such as food, feed, bio-based products, and bioenergy."
Finding strategies to replace petrochemical products with bio-based products should be a priority for every environmentally conscious homeowner. In the specific case of home insulation, moving away from foam insulations made from fossil fuels is relatively straightforward due to the availability of natural, bio-based insulation alternatives.
Sheep's wool insulation is natural insulation made from real sheep’s wool. Sheep in Iceland can withstand brutally cold winters, thanks to their wool’s unique properties. It’s crimped and folded, forming millions of tiny air pockets that create a thermal barrier against extreme hot or extreme cold. Sheep’s wool insulation manufacturers build on that principle to develop batts or insulation rolls from individual wool fibers. Most industrial wool insulation is held together with polyester adhesive, but you can find 100% natural products.
Sheep’s wool insulation is often confused with the VERY different mineral wool insulation, made from molten basalt or iron ore fibers.
The thought of a sheep being harmed to help build your home is an absolute no-go. That’s why you want to choose a manufacturer that takes Animal Welfare practices very seriously. Like the standard wool exporter, New Zealand, most nations ban a harmful practice called “mulesing.” Responsible sheep farming is more than possible and pretty standard nowadays, so don’t be afraid to do careful research on where your manufacturer gets their wool.
Most industrially produced wool insulation products are held together by some polyester adhesive, though it is possible to find wool insulation from 100 percent natural products. High-quality wool, such as that from Merino sheep, can be prohibitively expensive. Thus, most sheep wool for insulation purposes is sourced from black wool sheep without other uses. It is also important to differentiate natural sheep wool insulation from rock wool or mineral wool. The latter is fiber-based, loose-fill insulation made from the fibers of molten basalt or the recycled fibers of iron-ore waste.
Sheep's wool insulation is that this natural material can also naturally regulate humidity levels in the home. If you ever touch a sheep outside during a rainstorm, you will probably be amazed that fine that their wool will feel dry to the touch. The unique consistency of sheep wool allows this natural product to absorb around 33 percent of its weight in moisture without ever losing its insulating ability. Whereas exposure to water or humidity can damage fiberglass and other common types of loose-fill insulation, this isn't a concern with sheep wool.
The hygroscopic nature of sheep wool insulation can also help purify your indoor air, especially for homes that suffer from excess moisture or humidity. Besides capturing excess humidity, sheep wool can also amazingly pull and store harmful VOCs such as nitrogen dioxide and formaldehyde that compromise your indoor air quality. This air-cleansing ability is possible because of the natural proteins in sheep wool that create a chemisorption process.
Sheep wool offers several sustainability benefits that we have outlined above. On the downside, however, sheep wool batts can be more expensive than other insulation options. Raw sheep wool can be sourced relatively inexpensively. Because many building experts still consider sheep wool insulation to be a sustainable novelty item, manufacturing does drive up the cost. As more homeowners discover the benefits of this natural insulation option, prices should continue to drop.
In terms of overall thermal property and insulation capacity, sheep wool insulation products are not the best on the market. According to the Healthy House Institute, "sheep wool insulation has an R-value of approximately 3.5 to 3.8 per inch of material thickness, 0.3 to 0.6 points higher than fiberglass, cellulose, or mineral wool." For comparison's sake, vacuum insulated panels can have an R-Value of R-45 per inch, while polyurethane and phenolic foam insulations usually obtain R-7 per inch. For homeowners in cold climates, wool insulation batts can still be used. However, you will most likely need customized wall studs to achieve optimum insulation for the best thermal performance.
In terms of its manufacturing process, sheep’s wool boasts one of the least energy-intensive processes among insulation products. It’s a natural material that goes through limited processing outside of spinning, bonding, and some chemical treatments to make it resistant to critters. Some manufacturers claim that wool’s embodied energy is less than half of cellulose insulation. Studies suggest that "sheep wool requires less than 15% of the energy used to manufacture glass wool."
Besides being a 100 percent natural product, sustainably and regeneratively-grazed sheep on healthy pastures can capture carbon dioxide from the atmosphere and sequester it in the soil. Increased demand for sheep wool insulation can stimulate local economies and give local farmers a new product from the livestock they raise.
Since sheep’s wool insulation is still relatively new to North America, the material might have to travel long distances to reach home. This adds to the embodied energy of sheep’s wool. Be mindful of where the raw material is coming from and your distance from the manufacturer.
Besides coming from a regenerative source, sheep wool is also an excellent insulator. The millions of tiny air pockets can trap air, thus creating a thermal barrier from outside temperatures. When combined with different polymers or glues to hold the fibers together, sheep wool insulation can be installed in almost any stud-built home. It is also helpful for attic and loft insulation.
The R-value of sheep's wool insulation ranges between 3.5 and 3.8 per inch. On average, sheep's wool insulation is approximately 0.3 to 0.6 points higher than alternative insulation options such as mineral wool, cellulose, and fiberglass. The additional R-value is primarily due to sheep wool insulation's crimped nature, which traps air in millions of tiny bubbles.
Sheep's wool insulation is naturally resistant to mold and mildew due to its natural ability to wick moisture. While other insulation types may be susceptible to moisture build-up leading to mold and mildew, sheep's wool fibers allow moisture to pass through without retaining it.
Untreated sheep's wool can attract moths and other insects. Most sheep's wool insulation is washed and treated with non-toxic ingredients that are often odorless and contain no volatile solvents.
The type of insulation you use does not necessarily increase the likelihood of attracting rodents. Rodents search for dry and cool areas to escape from the heat, wetness, or cold. A well-sealed building envelope is your best line of defense against rodents.
Sheep's wool insulation may emit a faint smell for up to three days, but it is not harmful nor unpleasant. In comparison, many homeowners who have used sheep's wool insulation compare it to a new carpet smell.
Sheep's wool has naturally high nitrogen and water content, so it needs high oxygen levels to burn. When wool heats up and combusts, its cell membrane structure swells, forming an insulating layer that prevents flame spread. Most sheep’s wool insulation products meet Class A building code for flame spread and smoke development, putting it at the front of the pack along with cellulose, mineral wool, and fiberglass insulation.
There are two types of sheep's wool batt insulation, one made with a mix of wool and poly fibers, and the other, which is made of 100% wool. If you get the blend of wool and poly fibers, make sure you determine where and what those fibers are made from. Several manufacturers do take the opportunity to use recycled polyester instead of using virgin materials in their blends.
The composition of the batt is essential because it also will dictate how it’s installed. Wool and poly mixes will typically have the friction fit installation used with other batts like fiberglass and mineral wool. If you opt for a 100% wool product, you will need to install it a bit differently.
Let's point out the obvious with this install. You do not need to use ANY protective equipment - and that feels pretty darn good and liberating when you think about it. It’s a departure from what we’re used to with insulation products. Some products like spray foam need complete respiratory protection and other batt products where you need a mask, safety glasses, and gloves at a minimum.
These particular batts need a few staples to stay in place, and that’s all that’s required. Getting around wiring or boxes is easy to solve, and the layers of wool in these batts separate in a much cleaner way than fiberglass or mineral wool - so it’s pretty flexible to work with.
Some builders might say that it could take longer to install these types of batts, and they might be right. Still, our experience is that it’s much more flexible and friendly to play with. We also believe that prioritizing the installers' health and comfort when installing products like this is just as important as any additional time it might take to throw in a few staples.
Using a natural alternative for insulation should also be a long-term solution. Having to replace your insulation every couple of years would be a considerable expense that most homeowners would not be able to make. Fortunately, sheep wool insulation, when properly installed, can last a lifetime. Its ability to naturally absorb and exude moisture and water vapor can be advantageous, especially in wet climates. Even at the end of its lifetime, sheep wool insulation will be 100 percent biodegradable.
If you plan to build a new home or undertake a significant energy efficiency renovation, sheep wool insulation might be worth considering. Check out this article for some recommendations on some of the best companies that manufacture ready-to-use sheep wool insulation.
Tobias runs an agroecology farm and a natural building collective in the mountains of El Salvador. He specializes in earthen construction methods and uses permaculture design methods to integrate structures into the sustainability of the landscape.