Wool insulation is made solely from sheep wool fibres that are either mechanically held together or bonded using up to 12% polyester adhesive to form insulating batts, rolls and ropes. Batts are commonly used in timber-frame buildings, rolls for lofts and ropes are primarily used between the logs in log home

Log home

A log home is structurally identical to a log cabin...

s. Wool insulation is used for both thermal and acoustic insulating applications. Sheep wool is a natural, sustainable, renewable, theoretically recyclable material and totally biodegradable that does not endanger the health of people or the environment. Wool is a highly effective insulating material that has been used for years insulating people in the form of clothing. Mongolian nomads also used felted and woven sheep wool pads as an insulating layer on the walls and floors of their dwellings called, ger or yurt

Yurt

A yurt is a portable, bent wood-framed dwelling structure traditionally used by Turkic nomads in the steppes of Central Asia. The structure comprises a crown or compression wheel usually steam bent, supported by roof ribs which are bent down at the end where they meet the lattice wall...

s. Presently the use of wool for insulation is starting to rise in popularity. It is used more in Europe, Australia and Canada than it is the United States; manufacturers are, however, trying to expand their distribution to the US.

Insulating qualities

Sheep wool is a natural insulator because it has a crimped nature which traps air in millions of tiny pockets. Air is an excellent insulator since it does not conduct or disperse heat well. Sheep wool insulation has an R-value

R-value (insulation)

The R-value is a measure of thermal resistance used in the building and construction industry. Under uniform conditions it is the ratio of the temperature difference across an insulator and the heat flux through it or R = \Delta T/\dot Q_A.The R-value being discussed is the unit thermal resistance...

 (resistance to heat flow) of approximately 3.5 to 3.8 per inch of material thickness which is 0.3 to 0.6 points higher than some glasswool, cellulose, and some mineral wool .The crimp also allows the wool to retain its structure and overall thickness instead of breaking down and settling like many other insulating materials. Wool is a hygroscopic material which means that it is thought to absorb up to 30% to 40% of its own weight in moisture without becoming wet to the touch. This is also claimed as a performance benefit by many wool insulation manufacturers but the attribute remains unproven in building applications. . This moisture absorption is unique to sheep wool and does not compromise the wool's insulating abilities unlike cellulose

Cellulose

Cellulose is an organic compound with the formula , a polysaccharide consisting of a linear chain of several hundred to over ten thousand β linked D-glucose units....

 or fiberglass

Fiberglass

Glass fiber is a material consisting of numerous extremely fine fibers of glass.Glassmakers throughout history have experimented with glass fibers, but mass manufacture of glass fiber was only made possible with the invention of finer machine tooling...

 insulation. When used as acoustic insulation wool provides rates starting at 44dB for a 60mm (2.4in) thick partition, and goes up to 53dB for a 100mm (4in) thickness. Wool has a long life span and can be used over and over again. Wool also has a low manufacturing energy at approximately 15 megajoules per kg of material produced. The low manufacturing energy of wool is just over half of that of cellulose insulation and practically one sixth of the manufacturing energy required to produce mineral wool, however, if one takes into account the embodied energy of the whole lifecycle, the polyester in the product alone has more embodied energy than mineral wool. The issues of transportation energy costs need to be factored in, as the embodied energy

Embodied energy

Embodied energy is defined as the sum of energy inputs that was used in the work to make any product, from the point of extraction and refining materials, bringing it to market, and disposal / re-purposing of it...

 figures usually do not consider this. Consumers must think about both transportation stages, pre-production, as a raw material, and post-production as insulation, to be careful to choose a manufacturer that is as close as possible to the building site.

Health considerations

Wool is not irritating to the respiratory system or the skin like fiberglass and other alternative insulating materials because its fibers are more than 30 micrometres thick which is too big to be a health risk; although it should be pointed out that conventional alternatives such as glasswool are also larger than the potentially carcinogenic fibers which are 1 to 4 micrometres thick. Wool insulation also may help prevent the sick building syndrome

Sick building syndrome

Sick building syndrome is a combination of ailments associated with an individual's place of work or residence. A 1984 World Health Organization report into the syndrome suggested up to 30% of new and remodeled buildings worldwide may be linked to symptoms of SBS...

 because it is claimed to trap substances like formaldehyde

Formaldehyde

Formaldehyde is an organic compound with the formula CH2O. It is the simplest aldehyde, hence its systematic name methanal.Formaldehyde is a colorless gas with a characteristic pungent odor. It is an important precursor to many other chemical compounds, especially for polymers...

, nitrogen dioxide

Nitrogen dioxide

Nitrogen dioxide is the chemical compound with the formula it is one of several nitrogen oxides. is an intermediate in the industrial synthesis of nitric acid, millions of tons of which are produced each year. This reddish-brown toxic gas has a characteristic sharp, biting odor and is a prominent...

 and sulfur dioxide

Sulfur dioxide

Sulfur dioxide is the chemical compound with the formula . It is released by volcanoes and in various industrial processes. Since coal and petroleum often contain sulfur compounds, their combustion generates sulfur dioxide unless the sulfur compounds are removed before burning the fuel...

 emitted by other common building materials and combustion processes. Wool is also naturally resistant to mold, unlike cellulose and cotton used as insulation. Sheep wool is naturally flame retardant

Flame retardant

Flame retardants are chemicals used in thermoplastics, thermosets, textiles and coatings that inhibit or resist the spread of fire. These can be separated into several different classes of chemicals:...

, self extinguishing and won’t melt but unfortunately the polyester in some hybrid wool based insulation products make them more flammable than conventional insulation alternatives. Because wool insulation is mechanically held together or bonded with polyester no chemicals or glues are needed. True Sheep wool insulation is biodegradableunlike mixed fibre alternatives. With the increase of municipal composting facilities available it is now relatively easy to compost at the end of is life. Used sheep wool insulation, can be composted without causing harm to the environment, but unfortunately it may produce the greenhouse gas methane if consigned to landfill.

Building considerations

Wool insulation commonly comes in rolls of batts or ropes with varied widths and thicknesses depending on the manufacturer. Generally, wool batts have thicknesses of 50 mm (2 in) to 100mm (4 in), with widths of 400 mm (16in) and 600 mm (24 in), and lengths of 4000 mm (13 ft 4 in), 5000 mm (16 ft 8 in), 6000 mm (20ft) and 7200 mm (24 ft). The widths of 16 in and 24 in are the standard measurements between studs in a stud frame wall. Most manufacturers provide custom sizes as well and batts and ropes are easy to cut once on site. Wool insulation can be used in the roof, walls and floors of any building type as long as there are spaces to put the insulation in. The construction costs when installing wool insulation are marginally lower due to having no need for protective gloves, this also makes installation slightly faster but unfortunately the purchase costs are several times higher than conventional alternatives. Installing wool insulation is very similar to installing conventional insulation batts, it can be held into place with staples or it can be friction-fit which involves cutting the insulation slightly bigger than the space it occupies, using friction to hold it in place.

Environmental factors

There are some primary environmental factors that need to be considered when looking for a source of wool, such as the way the flock is treated for pesticides, the chemicals used in the treatment of the wool after shearing, and the distance from the source to its final destination. Sheep are often treated with insecticide and fungicide in a process called dipping. This leaves a residue on the fleece and can result in groundwater contamination if used improperly. These residues are often washed off once the fleece is sheared, but this results in three byproducts, grease, liquor, and sludge. The first two can be safely disposed of, but the latter contains remnants of the pesticides which cause a concern for disposal. Sheepswool insulation is often treated with Borax

Borax

Borax, also known as sodium borate, sodium tetraborate, or disodium tetraborate, is an important boron compound, a mineral, and a salt of boric acid. It is usually a white powder consisting of soft colorless crystals that dissolve easily in water.Borax has a wide variety of uses...

to enhance its fire retardant and pest repellent qualities. The level of Borax is relatively low only 4% dry weight although the scouring baths have a higher load of 8% to 9%. Borax mining employs one of the cleanest mining techniques available but Borax is increasingly coming into focus as a suspected reproductive toxin having been considered relatively safe for many years; animal ingestion studies in several species, at high doses, indicate that borates cause reproductive and developmental effects. The most significant exposure route for humans is inhalation which raises questions over whether dust from wool insulation could lead to a significant exposure to humans; probably unlikely for anyone except professional installers.