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Last edited 26 May 2022
Wood and insulation
Insulation can be applied to roofs, walls and floors. When installed correctly it creates a cosy environment and saves on energy bills. However, for insulation to do the best job it can, it needs to work well in relation to other systems in the building fabric such as ventilation and air tightness. If all of these areas are considered during the design stage it can make for a much healthier home.
Wood fibre insulation is natural and natural fibre insulation has been used for thousands of years. Wood fibre is made from tiny cellulose microfibres held together with a lignin resin, a natural resin that is part of the tree.
The benefit of this is that wood fibre allows moisture movement, which is essential for the building fabric. Combined with good ventilation and air tightness systems, vapour can transfer through the building fabric allowing for breathability. In this way, moisture levels can be maintained at the optimum level and the build-up of damp and mould is decreased.
There are many factors to consider when bringing all of these systems together. Humidity and moisture levels are ever changing and the materials chosen should respond and work together to achieve the best results. This needs to be analysed at the design stage to ensure the systems will work.
 How wood fibre insulation works
Wood fibre insulation can be manufactured in the form of a board (either wet formed with no binder or dry formed with binder, but with no flame retardant chemicals used in either), or as flexible wood fibre. The latter is a thermally-bonded, non-woven product.
The different ways of manufacturing wood fibre insulation allow for varied densities, compressive strength, heat storage, and moisture movement. This means it can be used for a range of construction projects.
Wood fibre insulation works well with timber frame buildings. The way the insulation can be fitted around the openings in the frame can achieve very low thermal conductivity values, in comparison with some other construction products, which can result in an 80% reduction in heat loss.
 The health benefits of wood fibre insulation
Indoor air quality is high on the health agenda, and even though most people spend 90% of their time indoors, internal environments aren’t always the healthiest. Volatile organic compounds (VOCs) are in the air that we breathe and when indoors the level is often two to three times higher. VOCs are commonly released from paints and varnishes, adhesives, wood products, cleaning products, furniture and insulation.
Formaldehyde is a naturally occurring VOC and is made by the human body. It’s used to form other chemicals and is found in many of the products listed above. Though all species of wood contain and emit some formaldehyde, over-exposure can be harmful to humans.
Having a well-ventilated building with breathable insulation that manages temperature, humidity and pollution levels makes a significant difference and helps to manage the impact of this harmful gas. Wood fibre insulation is ideal as part of a system to improve overall indoor air quality and make a home healthier.
 Other qualities of wood fibre insulation
Wood fibre insulation’s thermal properties are impressive. The high density means heat is stored during warmer periods and released during colder periods as the external walls cool, hence lower energy bills.
It also has great acoustic qualities as wood fibre insulation absorbs sound and so makes for a quieter living space. It also has naturally fire-resistant properties and can withstand high temperatures.
 Examples of buildings with wood fibre insulation
Passivhaus homes in Norfolk were built using 100 mm wood fibre insulation boards which were installed externally over a 195 mm deep insulated timber frame. This minimised thermal bridging on the floor junctions and around the windows, improving the C-value and the overall U-value.
Proving wood fibre insulation isn’t just for new-builds with perfectly smooth walls, a draughty Victorian terrace underwent a complete refurbishment and has benefited from an 88% reduction in heating bills. Rigid wood fibre board was used on the front and flexible wood fibre wool on the rear of the board. This combination moulded itself to the shape of the uneven wall surface so there was no need to render it flat first.
Wood fibre insulation works for more than just homes and helped to transform the Edinburgh Centre for Carbon Innovation, an 18th-century building. A cross laminated timber frame and floor panel system was used with a combination of flexible wood fibre batts and rigid fibreboard with an internal OSB airtight layer. This enabled an historic building to be restored rather than demolished.
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