A sample sheep wool insulation batt.

Wool insulation is made from sheep wool that is mechanically bonded together to form insulating batts and ropes. Batts are commonly used in timber-frame buildings and ropes are primarily used between the logs in log homes. Wool insulation is used for both thermal and acoustic insulating applications. Sheep wool is a natural, sustainable, renewable, recyclable material that does not endanger the health of people or the environment[1]. 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 than it is the United States; manufacturers are, however, trying to expand their distribution to the US.

Insulating qualities Edit

Sheep wool is a natural insulator because it has a crimped nature which traps air in millions of tiny pockets. Sheep wool insulation has an R-value (resistance to heat flow) of approximately 3.5 to 3.8 per inch of material thickness[2] [3] which is 0.3 to 0.6 points higher than fiberglass, cellulose, or mineral wool [4].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 will absorb up to 30% to 40% of its own weight in moisture without becoming wet to the touch[1] [5]. This moisture absorption is unique to sheep wool and does not compromise the wool's insulating abilities unlike cellulose or fiberglass 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[1]. Wool has a long life span and can be used over and over again. Wool also has a low embodied energy at approximately 15 kilowatt hours per cube meter of material produced. The low embodied energy of wool is just over half of that of cellulose insulation and practically one sixth of the embodied energy required to produce mineral wool. However, the issues of transportation energy costs need to be factored in, as the embodied energy 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[6].

Health considerations Edit

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; potentially carcinogenic fibers are 1 to 4 micrometres thick. Wool insulation also helps prevent the sick building syndrome because it permanently traps substances like formaldehyde, nitrogen dioxide and sulfur dioxide emitted by other common building materials and combustion processes[1]. Wool is also naturally resistant to mold, unlike cellulose, cotton and other fibers used as insulation. Sheep wool is naturally flame retardant, self extinguishing and won’t melt. In the case that the wool does ignite, its inflammation point is 560 degrees Celsius, it will not emit any toxic gases. Because wool insulation is mechanically bonded there are no chemicals or glues needed. Sheep wool is biodegradable so used wool insulation, if it not going to be recycled, can be composted without causing harm to the environment.

Building considerations Edit

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 lower due to having no need for protective clothing or respiratory equipment, this also makes installation slightly faster. 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 Edit

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[7]. 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. When used in insulation wool is often treated with Borax to enhance its fire retardant and pest repellent qualities. Borax mining employs one of the cleanest mining techniques available[8] and the Borax product has a low toxicity with no need for special safety precautions when handling it and requiring nothing more than washing hands and changing clothes daily after contact[9].

References Edit

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