Tom Taylor, Principal Consultant, BRE, explains how excellence in building envelope specification can help achieve BREEAM ratings.
The specification of the building envelope has implications for performance against several BREEAM New Construction assessment issues and could potentially have a significant impact in determining the overall BREEAM rating for a project.
The thermal performance of the building envelope is a significant factor in the assessment of energy use and carbon emissions under issue Ene01 in the energy category. The Ene01 energy calculation methodology uses a ‘triple metric’ approach that makes it necessary to consider each stage of the energy hierarchy (reducing energy demand, using energy efficiently, and supplying energy from renewable sources) in order to achieve a high overall Ene01 score. The first step of reducing energy demand is of particular importance since any improvements made here will not only increase the demand parameter score, but also feed through and help improve performance against the other two parameters. This means that following a ‘fabric first’ approach through ensuring high levels of thermal performance when specifying the building envelope will maximise the potential to score well against Ene01 and the energy category as a whole.
The materials category assesses the specification of materials against issues including life cycle impacts, procurement and resilience. The assessment of these issues is undertaken for the main building elements which specifically include the external walls, windows and roof and, as such, the specification of the building envelope as a whole will potentially make a significant contribution to the overall materials category score. In particular, the selection of materials that have been responsibly sourced have a relatively low environmental impact over the life cycle of the building, and that limit material degradation due to environmental factors, will help to improve the materials category score and potentially the overall BREEAM rating.
In addition to having a significant influence on both the energy and materials category scores, the specification of the building envelope will affect other assessment issues including ‘thermal comfort’ and ‘acoustic performance’ within the health and wellbeing category, and could potentially even affect others like ‘ecological value’ and ‘surface water runoff’ through the specification of green roofs or walls. Given the wide range of assessment issues that are affected, it is clear that the design and specification of the building envelope is a key part of a BREEAM assessment, and one that presents a significant opportunity for improving the overall BREEAM rating.