Britain's best source of building product information

Improving the energy efficiency, as well as the sustainability of homes has never been more important and the drive to improve the standard of new build properties in this area has been strongly backed by the government in the last few years.

Building Regulations, as well as initiatives such as the recently introduced Code for Sustainable Homes have all been geared to encourage housebuilders and developers to use more energy efficient, sustainable building methods and improve the performance of the buildings they construct.

As such, the performance of insulation products, both in terms of their thermal efficiency and sustainability credentials, has come under much closer scrutiny. There are many different types of insulations used throughout the UK, the most common of which are synthetic. These include extruded polystyrene (XPS), expanded polystyrene (EPS), polyurethane (PUR), polyisocyanurate (PIR), multi-foil insulation and glass and rock fibre.

However, high quality natural, ecologically sound insulation products, such as flax, hemp, sheepswool and woodfibre board are now being manufactured for mainstream construction. These healthy and sustainable insulation products have proved to outperform synthetic alternatives when it comes to durability, specific heat capacity and thermal mass, and breathability, which means that they can provide better thermal performance, as well as protect the long-term health of the building fabric and its residents.

As a result, they are becoming much more widely used, as housebuilders, architects and specifiers realise that synthetic insulation products are not necessarily providing the best solution for modern, energy efficient and sustainable homes.

When it comes to durability, natural, air-based fibre insulations have proved to be extremely strong and durable, and can easily last 100 years in the correct environment. Contrastingly, many glass and rock fibre based insulation products collapse and degrade over just a few years, significantly diminishing their thermal performance. There is also doubt over the longevity of the gases in closed cell insulation, which may off gas over time, reducing the thermal resistance of the insulation.

Natural fibre insulations also outperform synthetic products in terms of specific heat capacity. Most natural fibres have a specific heat capacity of about 2,000J/kgK, whereas mineral wool only has 800J/kgK and plastic insulations only have 1,400J/kgK.

When combined with the greater density of natural insulations, this enhanced performance means that their thermal mass is considerably higher than synthetic alternatives. Natural fibre batts, such as hemp or sheepswool, typically have eight times the thermal mass of mineral fibre, while woodfibre boards have over 50 times the thermal mass of mineral wool and around 40 times that of most plastic insulation boards.

The ability of a building envelope to ‘breath’ is a crucial part of maintaining the health of a building and its inhabitants. As a critical component of the building fabric, ensuring insulation is breathable, therefore, is essential.

The problem of trapped moisture in buildings has grown in recent years, not least as a result of increasingly stringent Building Regulations for energy efficiency, which have led to the combination of greater levels of insulation with vastly more airtightness in the external shell.

If the building shell is not designed and constructed correctly, these factors increase the risk of moisture being trapped significantly. They also put far more emphasis on the need for well designed and maintained ventilation systems. However, to rely solely on ventilation systems to ensure the health and breathability of a building is an unsafe strategy.

It has been estimated that 75% of building failures are due to water. This damage, which effects both building performance and human health, is usually in the form of rainwater penetration, internal or interstitial moisture condensation or interior surface condensation. For example, damp in external walls will considerably lower their thermal performance, while interior surface condensation causes moulds, which are harmful to a building’s inhabitants.

There are three key elements of breathability. These are hygroscopicity, a material’s ability to absorb and release water vapour as the relative humidity changes, capillarity, a material’s ability to absorb and release water as a liquid, and vapour permeability, a material’s ability to allow water vapour to pass through it. Different types of insulation offer very different levels of performance in each of these areas.

For example, while mineral wool is very vapour permeable compared to foil faced plastic insulation materials, which do not exhibit any breathable characteristics, it has very little hygroscopic capacity and limited capillarity. 

Natural fibre insulations, however, such as flax, hemp, sheepswool and woodfibre board, are fully vapour permeable, have excellent hygroscopic qualities and good capillarity. As natural fibre insulations offer all three of the ‘breathability’ qualities, they are able to deal with water as a vapour and a liquid far more effectively than both mineral wool and plastic insulations. Within the correct designs, this means that they can provide significant protection against moisture related building decay and sick building syndrome.

This breathable performance, combined with the enhanced durability, thermal storage, protection against overheating and sustainability credentials of ecologically sound, natural insulation products, makes them much more suited than synthetic insulations to the construction of modern, energy efficient homes and buildings, particularly those built using lightweight structures, such as timber frame.

As such, housebuilders and developers across the UK are now turning to high performance ecologically sound insulation products to help them significantly improve the performance of the buildings they construct, as well as meet the government’s increasingly demanding sustainability and energy efficiency agenda.