Modern construction methods take a far more holistic approach to the issue of ‘thermal performance’. It is no longer just a case of adding more and more insulation to improve a building’s performance, indeed since the introduction in 2002 of the Part L2A England and Wales regulation change, which required a 0.25W/m²K roof and 0.35W/m²K wall, it was agreed by academia and industry alike that we had almost reached the point of diminishing return. Yes, more insulation could be added, but its contribution in reducing CO2 emissions was minimal and, in fact, the act of increasing the amount of insulation present in the building was beginning to have a negative impact in terms of increasing the embodied carbon of the overall build.
In other words, the deeper the insulation, the more weight is added to the supporting structure, extending build programmes, escalating overall costs, reducing return and making projects less appealing from an investment perspective.
So, if more insulation isn’t the answer, what is? Tests have proven that one of the primary causes of heat loss from a building is poor detailing. These details include junctions and interfaces such as drip flashings, gutters and parapets which, when poorly designed and installed, can lead to significant levels of thermal bridging, the transference of heat from the inside of a building to the outside.
To put this into context, some details such as drip flashings, which run around the entire perimeter of the building at the base of the walls can, if they are not designed and installed with care, act as huge heat conductors, drawing heat from the warm interior and allowing it to be wasted, by passing to the exterior of the building envelope. Thermal bridging also increases the risk of condensation inside the building.
As a result of this phenomenon, the issue of improved airtightness has become a key focus for developers and architects, both in striving to deliver increasingly efficient buildings for their clients and in meeting the ever-demanding enhancements to building regulations.
Pre-empting the issue at the building’s conception through the specification of thermally robust details, which mitigate this ‘heat-sink’ effect, can deliver a significant thermal performance increase, with previous schemes having seen benefits of up to 10%. This translates into a direct saving on the building’s energy consumption, reducing PSI values and greatly enhancing compliance with building regulations.
From the perspective of airtightness, robust detailing can deliver a reduction in a building’s associated heat loss by as much as 30%. This realisation has led to some building envelope specialists assigning technical teams to develop a ‘gold standard’ which highlights precise detail specifications, along with their individual U and Psi values. This information can be included in the building’s SBEM (Simplified Building Energy Model) calculation, which is required for all buildings being constructed today in the UK.
In some cases, these details are delivered as standard, at no extra cost. However, where a choice of ‘standard’ and ‘enhanced’ details are on offer, the architect should carefully examine the options to determine which will provide the greatest protection against air leakage, prior to agreeing the specification.
By taking a holistic approach, the developer can improve on the notional building, as described in the national calculation methodology, without any increase in cost. In fact, because improved thermal detailing does not require additional weight to be put on the roof and walls, the size of the rafters, purlins and rails does not need to be increased. All of this contributes to enhancing the building’s thermal performance while at the same time improving the overall build programme, which reduces prelims and attendances.