Sep 19, 2019 Last Updated 10:52 AM, Aug 14, 2019

A critical junction for energy efficiency

Published in Technical Focus
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The UK is making good progress towards more energy-efficient buildings. But there are a couple of important factors that mean we risk hitting a proverbial glass ceiling with energy efficiency improvements. James Daley, Building Performance Analyst of Kingspan Insulated Panels explains more.


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.

To prepare for this change, 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.

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