Fintan Wallace from Ecological Building Systems discusses the importance of an airtight and windtight building envelope and the natural insulation solutions that can help reduce heating bills and improve comfort for social housing tenants.
The cost of heating a home remains a constant concern for social housing tenants, putting pressure on social housing providers to maximise the thermal performance of properties and help keep tenants out of fuel poverty.
Building regulations stipulate demanding U-values for new homes, and the Decent Homes agenda has helped to drive thermal performance through refurbishment projects too, but can more be done to ensure that social housing delivers its designed thermal performance and creates a healthier living environments for tenants?
FABRIC FIRST
The need to reduce energy bills for social housing properties has been a key driver for design and specification innovation in the sector. The introduction of energy efficient mechanical and electrical technologies has proved to be a significant step forward, with the specification of renewable technologies, HIU installations and LED lighting helping to drive down energy consumption.
The true value of these M&E innovations can only really be delivered, however, if they are installed as part of a holistic approach to ensuring
that energy is not wasted in the home. And when it comes to heating energy, the most effective way to ensure minimum wastage is by preventing heat from escaping.
It’s a specification philosophy that is referred to as ‘fabric first’: by maximising the thermal performance of the building envelope we can maximise the energy efficiency of the whole specification, which is better for the environment, better for the housing provider and better for the tenant.
MAXIMISING THERMAL PERFORMANCE
There are two factors that need to be delivered in parallel to achieve a successful fabric first specification in the wall and roof build-up of a home.
The first is the installation of an effective insulation that delivers high performance U-values with low thermal conductivity (Lambda value) to ensure that the warm air is trapped within the building. A highly insulated property with low thermal conductivity will not only maintain a warmer living environment in the winter, it will also minimise solar gain in the summer, creating a more comfortable, ambient home all year round.
It is vital, however, that the chosen wall and roof build up traps in heat and keeps out solar gain without trapping in moisture, because trapped moisture can be detrimental to tenants’ health and wellbeing, as well as becoming a potential cause of damage to the building fabric.
Alongside the Lambda value of the insulation, other factors vital to ensuring that a property meets its designed thermal performance are airtightness and windtightness.
Airtightness requires the close fitting and internal sealing of insulation material to avoid any gaps in the insulated envelope. Any gap can result in thermal bridging, and even an airtightness failure caused by a gap of just a few millimetres can have a dramatic negative impact on thermal performance, regardless of the insulation’s Lamdba credentials.
Windtightness, meanwhile, requires an effective membrane to provide a protective layer for the insulation, working like an anorak over a woolly jumper to maximise performance. Once again, it’s advisable to select a vapour open membrane that will prevent the loss of warm air while enabling moisture to escape.
A NATURAL PERFORMANCE
While natural insulation products have historically been seen as a niche, eco product, the benefits they offer in terms of building comfort make them an ideal solution for social housing. This is because they are free from chemical components and exploit natural properties of the material to offer both excellent Lambda values and breathability. As a result, they contribute to healthier buildings at lower risk of common problems such as damp, mould and condensation.
Among the proven types of natural insulation products available in the UK are wood fibre insulation and natural jute. Made by processing timber offcuts grown in sustainable forests, wood fibre can be fabricated with tongue and groove edges to facilitate a gap free installation, ensuring excellent U-value performance is achieved.
Meanwhile, natural jute insulation is manufactured from recycled ‘gunny bags’ used to transport cocoa to Europe. The fibres contain no proteins, which prevents any possibility of mould growth or insect infestations, and the insulation material is soft and flexible, enabling it to be used in a variety of locations, including between rafters, ceiling joists and floor joists, and in partitions and stud walls. Indeed, wood fibre and natural jute can be used in combination on a property as the rigid wood and flexible jute have varying advantages for different areas of the build.
SUSTAINABILITY & PERFORMANCE
As we look to ensure greater social sustainability through the provision of homes that stand the test of time, it’s important to remember that building performance also plays a critical role in the long term effectiveness of social housing environments and the health and wellbeing of those who live in them.
Fintan Wallace is the architectural technologist for Ecological Building Systems