Back to the Future: The story of Roofline Closure Systems
At a time when net zero targets are as hot a topic as ever before, making the UK’s housing stock as energy efficient as possible is a key issue, and the installation of external wall insulation (EWI) is one of the most cost-effective ways to achieve this.
This installation relies on a high level of skill from those working on it, good quality materials for them to work with, and a robust level of compliance with regulations. However, in recent years, a quirk of industry standards has created a scenario in which some of the homes most in need of EWI have found it impossible to get.
SETTING THE STANDARD
First introduced in June 2019, PAS 2030 and PAS 2035 were published in response to the Each Home Counts review, from which they were a key recommendation. These standards were developed by the British Standards Institute (BSI) and sponsored by Department for Energy Security and Net Zero (DESNZ) - with an industry-based steering group used to develop and agree content – and set out updated technical specifications for the installation of energy efficiency improvement measures, including EWI.
In principle, the standards stated that any energy efficiency measures installed under current government energy efficiency schemes must be compliant to ensure high quality installations and reduce the risk of unintended consequences, such as condensation or damp.
Prior to their introduction, the use of verge trims was the most common way in which installers provided protection to the top of the EWI system at the roofline. Historically, the use of metal verge trims has not been inherently problematic, but over the years a combination of malpractice, bad design and poor materials selection created a perfect storm of challenges. As a result, many of the installed verge trims did not adequately prevent the ingress of water and were difficult to maintain, which in many cases resulted in water ingress to the property or damage to the EWI system.
The writing was on the wall by this stage, and to help mitigate the risk of such damage, PAS 2030 effectively banned the use of verge trims, stating that “metal or plastic cappings and trims” should be avoided at the interfaces with roofs at eaves and verges.
While this solved one problem, it created another as it meant that the only remaining solution for many EWI-to-roof interfaces would require the roofline to be extended. Not only was this solution significantly more costly, time intensive and technically challenging for installers, but it was also in many cases – such as mid-terraced houses – not even possible.
The upshot of this was that many houses in dire need of EWI could not be treated, which posed a major issue at a time when the retrofitting of existing housing stock is playing a significant part of conversations around net zero and improving living conditions.
CHANGING THE APPROACH
Something had to give on this scenario, and the EWI industry’s response was to set up a working group tasked with squaring this particular circle. Senior figures from the National Insulation Association (NIA), the Solid Wall Insulation Guarantee Agency (SWIGA), and the Insulated Render and Cladding Association (INCA) – as well as businesses such as PermaRock - came together to find a way forward, working closely with Trustmark, the BSI and national government.
This working group set about developing sets of details that included enhanced weathering protection features such as multiple seals, reduced reliance on mastic, and effective overhangs that take into account the building exposure conditions. The group also looked into measures to limit heat losses through cold bridging, which would otherwise increase the risk of dampness and mould growth on internal surfaces.
One challenge that occurred was the “Catch 22” situation of needing to trial the group’s suggestions on houses that required EWI. Unfortunately the most appropriate houses suitable for trials were the very same ones for which PAS-compliance was required, and until the trials could be proved successful and accepted by the BSI, and other government bodies, they would not be compliant.
Liaising closely with government and the Local Authorities involved enabled the working group to obtain approval to undertake trials on a number of houses in ‘funded’ schemes, and once undertaken, the the eventual results were highly encouraging. The trials required establishing a design for the proposed ‘roofline closures’, gathering detailed descriptions of the materials employed, and recording the installation as staged photographs. All of these datapoints were collected as the supporting evidence to take the changes forward.
However, one key learning from the trial installation process was that the initial detail drawings that the working group had produced would be insufficient to provide solutions to every permutation of wall/roof interface that the industry may come across for installations.
The result is that - rather than attempting to produce details that would be all encompassing - a set of ‘design principles’ has been introduced that would enable compliant solutions to be created in every potential scenario.
This now means that EWI designers, installers and system providers have two pathways to compliance - adopt a standard detail as drawn and published in the so-called ‘weathering guide’ referred to in PAS2030 and PAS2035, or develop a bespoke solution, following the design principles, to suit the specific and particular needs of the roof/EWI junction in question.
THE WAY FORWARD
Following the conclusion of the general election in July, the new approach has been rolled out with the full support of DESNZ, introducing the phrase “roofline closure systems” and retiring the name “verge trims” due to the association with past failures.
In summary, these new roofline closure systems are more robust and address the issues of thermal bridging in line with PAS 2035 and 2030, while also reducing the requirement for maintenance by incorporating a minimum two layers of defence. Minimum materials specifications that must be adhered to have been drawn up, and there are now a host of supporting tools to assist the initial design and installation.
Whether or not this is the end of the story – time will tell.
As always, the guidance is only as good as those following it, and the industry needs to heed the lessons of the past in terms of ensuring that high standards of installation are maintained, and that the quality of materials remains paramount.
Dr Jeremy Richings is the technical director at PermaRock
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