Junctions Play Major Role in improving Buildings Overall Performance

The Issue

The UK is making good progress towards more energy-efficient buildings, and upcoming changes to the building regs will accelerate this positive change. But there are a couple of important factors that mean we risk hitting a proverbial glass ceiling with energy efficiency improvements.

The first is an incomplete understanding of the energy performance of whole building envelopes, and the relationships between different components in this regard. Energy modelling in all its forms is improving this, but it is still often too simplistic and based on inaccurate data and assumptions.

The second is a question of responsibility and oversight. While energy modelling is helping to foster a more holistic view of energy performance, more practical issues are holding back opportunities to improve building performance. The realities of multiple stakeholders in a building project mean many important elements, that impact overall performance, are being overlooked.

Junctions are the building components most vulnerable to these two factors.

Junctions typically occur at windows, doors, drips, eaves and verges. Because they form the joint between two different envelope sections, they are naturally more at risk of broken thermal continuity. Their energy performance is measured in Ψ (psi)-values, a linear measurement of heat transfer between different building components.

Unfortunately junction energy performance is still relatively poorly understood. Many in the industry are still unsure of how to manage the construction of junctions to maintain maximum thermal performance. Even worse, in response to this, Ψ-values are often over-compensated for in energy modelling, leading to buildings whose performance is underrepresented to clients.

This situation has occurred for a variety of reasons. While U-values were an obvious place to start when improving envelope efficiency, initially offering vast, measureable savings, the smaller immediate gains of Ψ-values were deemed too awkward by comparison, and got less attention,

But the days of focusing purely on U-values are numbered. As technical advances drive U-values closer to zero, uplifts will become smaller, and the gains, while still important, will become increasingly marginal.

In this context, the impact of junction efficiency to envelope performance as a whole will increase, bringing it to the fore.

The industry needs to get to grips with Ψ-values now to prepare for this change.

The Solution

The solution to this issue is simple; the industry must gain a better understanding of junctions and how they perform within the wider building envelope, and improve working practices to ensure these elements are being optimised.

There are three reasons why junction efficiency should be at the forefront of contractors’ minds. One is simply best practice; understanding junction efficiency will make for better, more energy-efficient buildings. Something the entire industry is striving for.

The second is economic. There is potential for a clear commercial advantage to those businesses willing to step ahead of the industry curve in understanding junctions and building with them in mind, particularly to meet the demands of the vanguard of clients, architects and energy assessors keen to create the next generation of improved buildings.

The third reason is risk. Often junctions mark the boundary between different contractor responsibilities, and not enough is understood about the management of and responsibilities for junction efficiency between multiple parties, meaning the overall energy performance of the building can be compromised at these vital points. As clients and assessors begin to understand the energy performance of their buildings more, questions will be asked of everybody involved in the building process if performance doesn’t stand up to increased scrutiny. There needs to be a more clearly defined chain of responsibility, from architect to main contractor to cladding contractor, to ensure optimum build quality.

That’s the reason for my role at Kingspan Insulated Panels. Our Technical Services Department recognises how our industry can benefit from better understanding Ψ-values, and we’ve acted accordingly. Customers can call our technical team at any time to get advice on the energy performance of junctions or product-specific Ψ-values to enable more accurate forecasting.

This is particularly pertinent for Simplified Building Energy Modelling (SBEM), where the default values used to calculate the junction efficiency of generic insulated panels are actually well below the performance levels of our products – potentially leading to underestimated energy performance. In fact, using actual Ψ-values for Kingspan products in a standard warehouse can reduce heat loss by 17% compared to default Ψ-values. Inputting the correct Ψ-values for these products leads to reduced capital cost immediately as internal plant (e.g. HVAC systems) are not oversized, as well as reduced operational costs from running these systems more efficiently at the optimal demands they were designed for. This is not just an advantage for the client; M&E contractors are able to offer more competitively-priced systems when they have this more complete understanding.

It’s true that, at the moment, failing to fully understand and manage junctions is not a major business risk to contractors. But as awareness among clients and assessors increases, and the general attention broadens from just U-values, junction performance is likely to come to the fore.

Understanding junctions now will protect businesses from falling behind as the industry makes that shift, and will help to improve the overall performance of our built environment. It’s time to understand Ψ-values.

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