As we work to deliver energy efficient buildings and meet the UK’s goal to become net zero carbon by 2050, one of the key challenges is ensuring new buildings meet performance expectations. In practice a “performance gap” can exist between the expected and actual energy performance and operational carbon emissions from buildings. This gap can be significant with research showing heating demand for new homes can be 100% - 150% than expected at the design stage.
In this article, we dig into the performance gap including:
- the key potential causes of underperformance
- how we can address these issues.
What are the causes of the performance gap?
The performance gap between the design and actual performance of buildings can occur for a range of reasons. Some of the most common relating to the insulation specification can include:
- Product substitution – during construction, products can be substituted for a variety of reasons. This can cause underperformance where the specified product is replaced with a lower performing alternative such as less thermally efficient insulation, but this information is not passed onto the energy assessor and therefore not reflected in design performance expectations.
- Unanticipated problem areas – in certain areas of the building envelope, unexpected issues can mean that the available space for insulation is reduced. This can mean thinner layers of insulation are used than required by the specification, or no insulation at all is installed in particularly challenging areas.
- Thermal bridges –where construction details for insulation measures at junctions and around openings are not considered during the design phase, this can lead to higher than expected losses as a result of thermal bridges.
- Poor workmanship – similarly, where insulation measures are fitted with gaps or cut inaccurately, it can provide paths for heat to easily by-pass the insulation layer leading to higher than anticipated heat losses.
How can we address the causes of the performance gap?
There are a range of solutions which can be deployed to address these potential issues.
Product substitution
If the insulation product within the original specification is unavailable, care should be taken to ensure the replacement provides an equivalent performance in key areas such as thermal and reaction to fire performance. Where this is not the case, building modelling should be updated to reflect this change. This will allow corrections to be made, for example, by fitting a greater thickness of insulation.
Problem areas
Where the available space is less than anticipated, problem solving solutions may be available to allow the required U-value to be met within the available depth.
For example, AlphaCore range products combine a Euroclass reaction to fire rating of A2-s1,d0 with a thermal conductivity of just 0.020 W/mK. This thermal conductivity is far lower than conventional façade insulation products with an equivalent reaction to fire rating. This can allow a project U-value to be met with a slimmer construction in problem areas where the available depth may be limited such as:
- where the is a close boundary with another building
- where the floor slab projects beyond the structural frame
- where a lift shaft projects beyond the structural frame
- where shear walls project beyond the structural frame.
Our OPTIM-R range of vacuum insulation panels (VIPs) can also provide a slim solution for challenging applications such as existing solid floors or roof terraces where an even transition must be maintained between internal and external floor heights. The VIPs have a thermal conductivity of just 0.007 W/mK, far lower than conventional alternatives. This can allow the desired thermal performance to be met with a very slim insulation system thickness.
The OPTIM-R E Inverted Roofing System features encapsulated VIPs which support easy manual handling and allow the desired U-value to be met with a slimmer system thickness than conventional extruded polystyrene (XPS) alternatives.
Thermal bridges
To support best practice, and ease compliance, it is recommended to use designed details for insulation measures at key junctions where possible. These ensure that a clear process sequence is provided for the installation team to allow them to deliver a construction which effectively reduces heat losses.
We have developed a range of calculated details for our key product ranges, supporting designers to achieve workable details with low levels of heat loss.
Browse our thermal detailing guides
Poor workmanship
Effective oversight of installations is also essential to ensure that insulation measures are correctly installed with no gaps or defects. As part of the recent updates to Part L of the Building Regulations in England and Wales, a new requirement was placed on installers to provide clear photographic evidence that insulation measures are correctly installed before they are covered on new homes. This approach can provide a basis to support improved onsite workmanship provided it is supported with effective action where poor installations are documented.
Learn more about compliance reports
Product awareness training and installation guides can also be a useful resource provided by manufacturers, enabling installers to understand proper installation processes and how to deal with any challenges appropriately without compromising overall performance.
Building performance evaluations
Alongside these specific solutions, the use of post completion building performance evaluations (BPE) is also an important step to allow the industry to properly address performance gap issues. By collecting this data, underperformance issues can be identified and addressed and these learnings can be shared with the wider industry. The British Standard BS 40101: 2022 has been developed to provide a clear process for planning, and carrying our these evaluations.
