Wool insulation

A sample sheep wool insulation batt.

Wool insulation is made from sheep wool fibres that are either mechanically held together or bonded using between 5% and 15% recycled 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 homes. Wool insulation is used for 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 yurts. Presently the use of wool for insulation is starting to rise in popularity. It is used more in Europe, Australia and Canada however it is now sold in the United States.

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 (16 in) and 600 mm (24 in), and lengths of 4000 mm (13 ft 4 in), 5000 mm (16 ft 8 in), 6000 mm (20 ft) 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 costs significantly more than conventional fiberglass insulation, but does not require the use of protective gloves, and may have significantly lower health risks to both the building occupants and the installation crew. It can be used in the roof, walls and floors of any building type as long as there are spaces to put the insulation in. 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

Sheep are no longer farmed primarily for their wool; however, they need to be clipped annually to protect the health of the animal. The wool used to manufacture insulation is the wool discarded as waste by other industries due to its colour or grade. As a controlled waste product it cannot be disposed of until it is cleaned. Hence the energy footprint of washing the wool is attributed to the livestock industry under PAS2050. 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.^[1] 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 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 8–9%.^[2] Borax mining employs one of the cleanest mining techniques available^[3] 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. There are some company's that use DE (Diatomaceous Earth) as pesticide. DE is believed to be harmless and is used in feed and animals to stave of peristalses. DE has the drawback of having to be applied in two steps to be effective and the wool having to be installed loose.^[4]

References

1. Cypermethrin sheep dip to be scrapped. environment-agency.gov.uk. 3 March 2010
2. Mike Madon – British Wool Textiles research undertaken 2007
3. Tom Laichas, A Conversation with Jared Diamond. worldhistoryconnected.press.uiuc.edu
4. http://proearthbuilders.com/Wool_Insulation.html