What is the performance gap?
‘The performance gap’ is a term given to any shortfall between the intended performance of a building and its performance in reality. This can be evidenced in any area of building design and specification. So, what is a performance gap? Ultimately, it means a building does not perform as designed, even though it has been signed off as complying with national building regulations.
Most commonly, discussions about performance discrepancies revolve around buildings losing more heat, consuming more energy, and/or being responsible for more greenhouse gas emissions than originally calculated and designed. Addressing performance gaps – and, by extension, seeing regulatory compliance as more than a tick-box exercise – is critical to buildings contributing to net-zero targets.
Read on to learn more about the building energy performance gap versus actual energy use in construction.
Why Are Performance Gaps Likely To Occur?
Generally speaking, the existence of gaps in performance points to a disconnect between the design process and the building construction. If the architect or design professional isn’t involved with the on-site operations, their ability to influence what happens during construction is extremely limited.
Factors Contributing to the Energy Performance Gap
There are a host of reasons why a performance gap might occur. This is something that the Passivhaus Standard seeks to address to create buildings that perform almost exactly as intended, even decades after first being constructed.
Here are a few factors contributing to your project not performing as well as intended despite meeting compliance requirements.
Workmanship Quality
A contractor might misread, not understand, or blatantly ignore elements of the design drawings. They might try to follow the drawings perfectly but may find the design difficult to build in reality.
Cost Cuts
The client might ask the contractor to make cost-saving decisions, leading to different products being chosen that don’t perform in the same way.
For example, contractors could opt for a thinner or less conductive material when implementing thermal breaks. This, in the long run, can be detrimental to heat loss prevention, increasing the overall energy consumption and not meeting building performance standards.
Environmental Unpredictability
A contributing factor to performance discrepancies is the use of unreliable weather data in forecasting. It can be difficult to develop buildings that can adapt to climate change and actually perform well within unpredictable changes.
That’s why reliable weather data is necessary for accurate energy demand calculations. Uncertainties in weather data can cause disparities in the project’s actual performance because of incorrect forecasting.
Occupant Habits
Considering occupant behaviour is essential when designing buildings. Occupants substantially impact the energy use of buildings since they directly affect energy consumption.
That’s why accurate behaviour modelling tools are required to reduce discrepancies and ensure more precise energy calculations.
How Does the Performance Gap Occur at Junction Details?
An element of the building fabric might not achieve its intended U-value once the building is constructed and in use. Similarly, a junction detail might suffer from a higher rate of heat loss than expected.
That means the real-world PSI value (Ψ-value) of the junction or thermal bridge is higher than the PSI value as designed and signed off as part of the compliance calculations.
If the building fabric elements achieve their U-values but PSI values don’t perform to the expected level, then the linear thermal bridges will account for a much greater proportion of the total heat loss. In the worst case, they could even be responsible for condensation and some mould growth if the surface temperature factor is incorrect.
Avoiding discrepancies in linear thermal bridging means designing details that can be understood on-site and, most importantly, built accurately.
Too often, junction detailing is still seen as complex or inaccessible. That makes it harder to ensure that you achieve the required PSI values in the finished building.
Enter thermal modelling software — a fast and accurate way to calculate important building values like linear thermal transmittance (br497).
How to Measure Performance Gaps?
Post-occupation studies are essential to determine whether buildings live up to their predicted output. This is done to understand the difference between the actual performance and the predicted calculations of buildings.
Essentially, performance gaps are measured by comparing the predicted outputs to the actual output after all variables have been implemented.
These results bring us a step closer to ensuring that the UK reaches its 2050 carbon reduction target of net zero emissions.
How Can We Close Performance Gaps?
It is important to take preemptive steps in order to reduce the potential for gaps in building performance. Here are a few considerations to address.
Utilise Technology
To ensure the most accurate energy calculations and deter human error, it’s best to consider useful PSI value software to increase accuracy when it comes to determining a building’s energy performance.
To prevent building performance gap issues, it’s vital that we take advantage of the accuracy and speed of building performance modelling tools.
Simplify performance compliance using comprehensive solutions that run analysis and project estimations. Using the output data will allow you to make evidence-based projections, provide clear, informed building instructions, and help reduce the performance gap of buildings.
Streamline Stakeholder Communication
Open channels of communication are essential throughout the entire building process, from design to construction. Ensure that everyone is on the same page and that you’ve set realistic expectations for energy targets to reduce the performance gap.
Energy loss needs to be at the forefront of decision-making, and these decisions need to be accurately and promptly communicated throughout the entire chain of command. Open communication will ensure that everyone is working toward the optimal energy performance of buildings.
For example, providing clear reasoning behind design decisions can help prevent changes during design execution. It’ll ensure that contractors understand that construction details need to be completely followed to avoid comprising pre-existing calculations.
Ensuring there is a continuous feedback loop is also a good way to improve existing processes and help prevent performance gap occurrences on future projects. It’s an ideal method to ensure you’re aware of how to avoid or rectify potential performance issues, even during the building design stage.
Set Quality Control Checks
Often, performance gap buildings are a result of little to no quality control.
Implementing quality control measures will ensure your project is built according to the design specifications and adheres to building performance specification guidelines. Quality control will ensure that the design specifications translate into the final product once constructed.
Reduce the possibility of performance gaps in buildings by:
- Continuously reviewing designs for compliance and clarity
- Conducting regular site inspections to identify construction issues or deviations
- Ensuring construction is following regulatory guidelines to meet compliance requirements
AutoPSI: Bridging the Performance Gap with Accurate Thermal Bridging Software
AutoPSI is a fully online thermal modelling tool that makes calculating Ψ values quicker and the detailing of junctions more reliable.
AutoPSI features a drag-and-drop interface that allows fully customisable junction details to be modelled, and all PSI values are calculated in accordance with relevant standards and conventions.
Accurate Ψ-values coupled with meeting recognised construction details is the best way to ensure an efficient building design. Following these conventions will help limit energy use and heat loss to reduce building performance gap occurrence.
Now that you know the answer to “What is a performance gap?’ and how to overcome it, try AutoPSI’s innovative and BRE-accredited PSI value software. Sign up for a 7 day free trial today to see how our software can help you.
