Natural insulation in listed properties
Many owners of older properties are familiar with the importance of breathability and using breathable natural fibre insulation (NFI). There are many additional reasons for using insulation made using materials such as sheep’s wool, wood fibre, hemp and straw.
Intuitively, the rationale for using NFI in traditional buildings is simple: they make use of materials in common use at the time of construction, so they work in sympathy with the fabric of older buildings. This is particularly important when it comes to maintaining a healthy moisture and humidity balance within the building fabric.
NFI’s breathe in a way no other insulation does. Not only is natural fibre insulation highly vapour-permeable, the fibres bind and release water molecules like tiny magnets depending on the humidity of the surrounding air. When this happens, the moisture is bound in a much less harmful form than liquid water droplets. This enables NFI to be truly breathable, helping prevent the accumulation of harmful moisture and ensuring the insulation performs consistently across a wide humidity range.
Heat loss
Most of us recognise the importance of insulation in preventing heat loss, saving energy and reducing operational carbon (the sum of the energy needed to heat, cool and light a property), but fewer connect insulation with other aspects of building performance. Insulation can account for more than 50% of the volume of the building fabric so it’s important to appreciate what insulation does. In fact, insulation and NFI’s in particular play a significant role in many aspects of a building’s performance, including energy efficiency, heat gain, acoustic comfort, sustainability, moisture balance, indoor air quality, buildability, durability and fire performance.
The acoustic properties of natural fibre insulation are often overlooked. Because of their irregular surface, shape and density, fibres such as sheep’s wool are very effective at disrupting sound. That’s one of the reasons why not need to be supported within timbers, a continuous layer of insulation can be achieved which eliminates thermal bridging. The most common rigid insulation is wood fibre or cork. Wood fibre is more widely available and cost efficient. Cork is also becoming a popular choice.
Thermafleece
Thermafleece British sheep’s wool is the most widely used flexible insulation in the UK, with flexible wood fibre and hemp also common. Flexible insulation is formed by combining natural fibres with a small about of binder fibre, which holds the insulation together and prevents slumping. This type of thermally bonded insulation is very durable and retains full breathability as the natural fibres are fully exposed to the surrounding air. The choice of fibre type largely depends on personal preference and cost, sheep’s wool often being the lowest cost NFI option. Flexible NFI can also be used in walls providing it is held within a timber stud frame.
When it comes to upgrading the thermal performance of existing buildings, it is important to look at each property on its own merits. The choice and availability of natural fibre insulation has never been greater. With established technologies and expertise within the UK, suppliers are able to provide comprehensive support to clients and professionals to ensure the most appropriate products and systems for each building. sheep’s wool and wood fibre insulation can provide acoustic performance comparable to the best mineral fibre products.
With natural fibre insulation available using a variety of materials such as wool, wood, hemp and straw it’s often a puzzle as to which one to use or which is best. There is a large element of personal preference, but it depends firstly on the where the insulation is to be used and the type of insulation required, whether it’s rigid, flexible or loose fibre.
Rigid, Flexible of Loose
Rigid insulation is particularly good for insulating walls and for use over or under rafters in roofs. Because the insulation does not need to be supported within timbers, a continuous layer of insulation can be achieved which eliminates thermal bridging. The most common rigid insulation is wood fibre or cork. Wood fibre is more widely available and cost efficient. Cork is also becoming a popular choice.
Thermafleece British sheep’s wool is the most widely used flexible insulation in the UK, with flexible wood fibre and hemp also common. Flexible insulation is formed by combining natural fibres with a small about of binder fibre, which holds the insulation together and prevents slumping. This type of thermally bonded insulation is very durable and retains full breathability as the natural fibres are fully exposed to the surrounding air. The choice of fibre type largely depends on personal preference and cost, sheep’s wool often being the lowest cost NFI option. Flexible NFI can also be used in walls providing it is held within a timber stud frame.
When it comes to upgrading the thermal performance of existing buildings, it is important to look at each property on its own merits. The choice and availability of natural fibre insulation has never been greater. With established technologies and expertise within the UK, suppliers are able to provide comprehensive support to clients and professionals to ensure the most appropriate products and systems for each building.
First Published in Listed Heritage Magazine. July 21
Mark Lynn is managing director of Cumbria-based Eden
Renewable Innovations and vice-chair of the Alliance for
Sustainable Building Products (ASBP).
15/07/2021