Neil Turner of Ecological Building Systems looks at why sustainable insulation offerings present a ‘natural choice’ for self-builders
Natural insulation materials are experiencing a resurgence as self-builders are increasingly seeking sustainable materials that can offer similar performance, but with lower environmental impact.
There are many performance benefits associated with natural insulation materials, which are becoming more widely known. These include low thermal diffusivity, which results in a reduction in summer overheating due to high specific heat capacity, high density and reasonable thermal conductivity. In addition, natural insulation materials like wood fibre can lead to a reduction in airborne acoustic noise and greater moisture diffusion openness, otherwise known as breathability. In addition, they have better carbon profiles than many other insulation materials.
Wood fibre insulation is currently experiencing a resurgence. An excellent insulator, it is made from post-industrial recycled wood chips, which may otherwise go into landfill and is suitable for a wide range of internal and external applications, as long as it is above ground level.
Natural insulation has a very low cradle to end of life Global Warming Potential (GWP) of 93.36kg CO2 equivalent/m3. Wood fibre insulation can also often be recycled at the end of life and when these impacts are taken into account (Section D of the life cycle assessment) Gutex Multitherm, for example, has a better than carbon zero GWP rating of -91.94kg CO2 equivalent/m3.
What is natural insulation?
Natural insulation materials originate purely from renewable resources and, as such, they have a significantly lower carbon footprint and a higher sequestered biogenic carbon content compared to conventional insulation options, such as foam or mineral wool.
Its environmental credentials are undeniable. With woodfibre insulation, when converting these waste wood chips into insulation, all of the sequestered biogenic carbon is locked into the building (1kg of dried timber can sequester 1.8kg CO2 Eq/kg). At the end of their useful life, these materials can often be recycled, contributing to a more circular economy and further boosting the Global Warming Potential (kg CO2/e) EPD rating for the natural fibre insulation product (Section D of the life cycle analysis according to EN15804).
Thermal regulation
The thermal mass and humidity-regulating properties of natural insulation can play a crucial role in maintaining comfortable indoor temperatures and reducing the risk of moisture-related issues in a home.
Compared to many other insulation materials, natural fibre insulation possesses a high specific heat capacity, which when combined with a relatively high density and reasonable thermal conductivity allows the absorption and storage of large amounts of thermal energy. This thermal mass can play a crucial role in mitigating overheating during the summer months, providing a more stable and comfortable indoor environment.
By choosing an insulation which is naturally able to store large amounts of thermal energy, self-builders can benefit from a high level of comfort all year round.
Natural insulation materials also help with acoustics, by absorbing sound waves, which reduces the transmission of noise between different spaces within a building. The lower density natural insulation products have excellent airborne noise reduction properties and the higher density products can be used to reduce impact noise reduction. It is the low dynamic stiffness and porous fibre structure, plus natural insulation’s inherent density that reduces airborne and impact noise and improves acoustics within a home.
Breathability
One of the main characteristics of natural insulation materials is their breathability (low moisture vapour diffusion resistance) and high moisture sorption/desorption properties. This provides more flexibility in designing building elements as there is no requirement for highly moisture vapour resistant barriers, which makes them a good solution for solid masonry construction. It also prevents the build-up of moisture within the building envelope, reducing the risk of interstitial condensation, mould, rot and other related problems. In combination with an effective ventilation system, natural insulation also contributes towards healthy indoor air quality, by allowing moisture from everyday activities, such as cooking and bathing, to escape from the building envelope via controlled diffusion.
In addition to being moisture vapour diffusion open, natural fibre insulation products tend to have a high degree of hygroscopicity. This allows moisture vapour to be absorbed, distributed, stored and then harmlessly released with changing indoor and outdoor climate conditions. This absorption and release of moisture by the insulation also helps regulate temperature fluctuations, hence providing a more comfortable living or working space.
The environmental impact and other performance benefits of natural insulation often outweigh the marginal differences in thermal conductivity. With careful design the inherent breathability of natural insulation means there is less need for maintenance as moisture build-up is prevented, so there are fewer damp issues.
Fire safety
As well as moisture prevention, natural fibre insulation has fire safety benefits too, as the products char on exposure to flame, rather than undergoing an explosive burning process. This surface char provides protection to the structure and slows down the penetration of heat and flame through the structure. It is possible to achieve an REI rating of up to 90 minutes tested from inside and outside according to EN13501-2 (BS476 Part 20-22).
A sustainable, energy efficient, natural insulation solution
While it may be the case that the initial cost of natural insulation can be higher than some synthetic options, this perspective often fails to consider the long-term benefits and the potential cost savings associated with these materials. The enhanced thermal and moisture management properties of natural insulation can lead to reduced energy consumption and lower maintenance costs over the lifetime of the building.
When it comes to choosing the best insulation material for a project, natural insulation makes a compelling choice. When you take into consideration heat capacity, breathability, thermal performance acoustics, fire safety and environmental impact, it is easy to see why natural insulation materials are rising in popularity.
The growing demand for more environmentally responsible materials is having a very positive impact on the variety of natural insulations available which means there is now a specific type of insulation available for most applications.
By harnessing the inherent properties of natural insulation, buildings can be created that not only reduce energy usage but also that contribute to a greener and healthier future.
Neil Turner is UK technical manager at Ecological Building Systems