Energy efficiency has long been a key consideration for school buildings but with rising fuel costs and new sustainability targets, it has arguably never been more important. Adam Ford, director of technical and marketing from leading building materials specialist, Building Product Design and Glidevale Protect, explains how adopting a ‘fabric first’ approach when designing new school buildings enables them to benefit from greater energy efficiency to meet new regulations without costing the earth to run.
A lesson in fabric first
What exactly is meant by the term ‘fabric first’? This approach is all about assessing the specified materials and components individually that collectively form the external building envelope and understanding how each element will contribute directly to the overall performance of a building, whether by improving energy efficiency or reducing long term maintenance costs.
Essentially, fabric first embraces the use of energy efficient materials to create low or zero carbon buildings, whether schools, workplaces or homes. The focus is on designing buildings that can make significant carbon and cost savings through the correct specification and installation of the products and materials that comprise the building structure and which last the lifetime of the building.
Putting the fabric first approach into practice
The growth of offsite construction in the education sector allows for greater accuracy of build to meet increasingly stringent sustainability targets and regulations that are being set by Government as part of the roadmap to achieve net zero. This is down to the fact that many of the ‘hidden’ products that play such a vital part in the efficiency of the building fabric can be installed under controlled factory conditions. This results in build efficiencies on-site, for example, consistent quality and a reduction in construction time.
Fabric first is usually associated with new builds to improve airtightness and thermal performance. Installing high-performance construction membranes is a key way for new school buildings to be made more efficient to heat, cool and run generally – which in turn will help provide a comfortable learning environment for staff and students.
The effectiveness of one or more reflective wall construction membranes, which provide an additional insulating layer, is dependent on the quality of the foil faced surface in terms of how it performs as a radiant barrier. A membrane featuring high quality aluminium used within a still airspace can significantly reduce radiant heat transfer and ensure the cavity becomes low emissivity, a vital part of energy efficiency in buildings. By combining reflective membranes as part of a system, insulation and footprint savings can be made whilst maintaining an overall low U-value for the building element. It can also help towards achieving a higher standard of construction such as Passivhaus.
A breath of fresh air – letting buildings breathe
A healthy school environment needs to be able to breathe and specifiers must balance achieving the right levels of airtightness with an appropriate ventilation strategy, to ensure the passage of fresh air to help control internal temperatures and CO₂ levels.
Airtightness can be boosted through the use of specialist air and vapour control layer membranes (AVCLs), which are installed on the warm side of the insulation to further limit heat loss.
As well as using an air and vapour control layer, an external wall breather membrane to the cold side of the insulation is also key. Not only can this help prevent water penetrating and damaging the exterior of the building during the construction, but breather membranes can significantly reduce the risk of interstitial condensation.
A good example of the fabric first approach being used to achieve Passivhaus certification in action is at the Early Learning and Childcare Centre in Blackridge, Scotland. Here the timber frame structure was specified with reflective construction membranes on both the external and internal walls, enabling low emissivity, still airspaces to be created within the wall structure with the foil surface of the membranes facing into the wall cavity. This helps to prevent heat loss from the structure and improve the wall’s overall thermal performance. The AVCL was installed with accompanying sealing tapes to achieve an airtightness test result of 0.6 ACH@ 50 Pa, ensuring Passivhaus compliance.
Adopting a fabric first approach and taking time to consider the correct specification of products at the outset of a project is key to creating a thermally efficient school that is cost-effective to run.
This article has also appeared in Education Design & Build July/August 2022