Natural Fibre Insulation – A sustainable and functional alternative?
As the need to make broader design considerations increases, greater attention is being given to lesser known technologies that offer wider ranging benefits compared to their conventional counterparts. One such technology is natural fibre insulation (NFI).
We are all very familiar with the use of natural fibres to keep us warm and comfortable so it is understandable that we should look to extend these benefits to the built environment. Fibres such as sheep’s wool, hemp, flax and wood fibres are commonly used in a variety of roof, wall and floor applications and their use is growing.
NFI’s can take the form of quilts, boards or loose-fill. Quilted insulation takes a form similar to mineral wool insulation is usually made from sheep’s wool, hemp, flax or jute. Wood fibreboards are made from fine wood fibres compressed together to form rigid boards whereas loose cellulose fibre can be blown into voids.
In the UK, Coarse British wool which is not suitable for fabric or carpet use is widely used for insulation. Its coarse irregular structure gives body to the insulation as well as helping absorb sound across a wider range of frequencies. It’s also very warm. When wool is combined with an inert binder to prevent slumping, the insulation will retain its loft and remain effective for the life of the building.
A well as reducing heat loss, insulation plays an important role in sound quality, air quality, moisture balance, health and sustainability within the building envelope. All this considered, the composition of the building’s insulation should not be overlooked.
Improving Sound Quality
NFI’s are well regarded for their superior sound insulation properties compared to similar man-made materials. This can be attributed to the relatively high density of NFI’s compared to their conventional counterparts and the irregular nature of natural fibres themselves.
Regulating Heat in the Summer Months
In summer, managing heat gain is often more important than preventing heat loss. Overheating is a frequently overlooked problem caused by factors such as low ventilation, solar gain through windows and penetrating heat. Heat penetrating the building fabric from outside to inside is particularly problematic when it reaches the inside of the building during the warmest parts of the day. This can be greatly reduced with the help of NFI’s.
The relatively high thermal mass of NFI’s allow them to slow the rate of heat penetration allowing the highest levels of heat to reach the inside of the building later in the day when temperatures are cooler. What’s more, unlike materials with very high thermal mass such as concrete, natural fibre insulation is able to lose its heat before the next cycle of daily heating begins which eliminates the risk of heat build up. In effect, natural insulation acts as both a heat shield and a heat buffer.
Moisture Balance
Natural fibres absorb water vapour by binding water within the chemical make-up of the fibre itself. This occurs through weak chemical bonds so the water actually becomes part of the natural fibre rather than condensing on the fibre surface as liquid water. Because the bonds between water and fibre are weak, the water can be easily liberated as humidity drops. This process enables natural fibres to hold nearly 30% of their weight in water and still be completely dry to the touch reducing risks associated with damp.
Natural fibres absorb and release moisture in response to relative humidity of the surrounding environment. As humidity increases natural fibres increase their moisture content binding the moisture in a safe dry form. As humidity drops, the reverse process occurs; allowing natural fibres to safely buffer moisture levels and allows NFI’s to transport moisture in a dry form.
Indoor Pollutants
As well as helping manage humidity levels, natural fibres such as wool can remove certain indoor air pollutants in particular formaldehyde, helping contribute towards a healthier indoor environment. Formaldehyde is used in binders and glues in many products. Wool permanently removes formaldehyde from the surrounding air in a two stage reaction that harmlessly liberates water.
In Conclusion
In the UK we have a healthy supply of local, rapidly renewable natural fibres. Natural fibres typically contain 50% non-fossil carbon so using these materials in durable end-uses such as insulation is an ideal way to store carbon whilst utilising a valuable local resource.
As demands become greater, increasing available options becomes ever more important. The search for new solutions is ongoing, one reason why the benefits of NFI’s are becoming increasingly well recognised.
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Written by Mark Lynn
Eden Renewable Innovations Ltd, Soulands Gate, Dacre, Penrith, Cumbria CA11 0JF
First published in Architects Data File May 2015
