In this guest post, Mitchell Gee, board member of both the Insulated Render and Cladding Association (INCA) and the Solid Wall Insulation Guarantee Agency (SWIGA), discusses the subject of roofline closure systems and their use on external wall insulation systems in accordance with PAS 2030/2035.
It’s been a long time coming but, at last, the use of roofline closure systems is to be recognised as an accepted detail on projects that require compliance with PAS 2030/2035. However, because of purdah – the restrictions placed on government in the run up to a General Election – a formal announcement cannot be made until after the election.
The change in terminology is deliberate; the products should no longer be referred to as ‘verge trims’ but ‘roofline closure systems’ (RCS), allowing for the fact that the robust details now provided go beyond the simple trims previously employed.
This has been a great example of the industry working together to achieve a common goal and, collectively, we thank those individuals who gave their time, at no cost, to produce a solution that was acceptable to DESNZ. There have been 48 different organisations involved over a 3-year period, meeting twice monthly. Numerous trials have been undertaken, demonstrating the effectiveness of the robust details that will be referenced in the PAS documents and featured in an updated version of the industry’s ‘External wall insulation specification for weathering and thermal bridge control guide’ – also to be published when government reconvenes.
For context, a verge trim was a capping detail similar to a sill that protects the head of an external wall insulation (EWI) system and which normally sits under the roof eaves or at the verge. It would usually only be required if the eaves or verge did not extend far enough to protect the head of the system. In an ideal situation, the insulation would be sealed under the roof soffit. If there was no soffit, or if there was insufficient soffit depth, then the most cost-effective solution was to introduce a verge trim.
The only other solution is to extend the roofline. This is not an issue if the planned works include re-roofing, but if not, extending the roofline is an expensive and intrusive procedure. But with PAS2030/2035 prohibiting the use of any metal or plastic profile or trim at the roofline, including verge trims, extending rooflines was the only solution. This increased the time and costs of installing EWI, thereby reducing the number of properties that could be installed within a given budget. Not only that, but nearly all social housing projects have private properties within the contract, making it difficult or impossible to undertake roofline extensions to the adjoining social properties.
Timescale & Rationale
Many of us ask why has it taken this long and why was it needed in the first place?
I’ve been working in the sector for 30 years and can take you to projects where verge trims installed all that time ago are still proving effective. So why has the verge trim got such a bad reputation? What has changed?
Properly designed and correctly fitted, a verge trim is a very effective method of capping an EWI system and should remain watertight for the lifetime of the building. It should go without saying that any product or system not correctly fitted is not going to perform effectively and is likely to fail. It is not difficult to correctly fit a verge trim.
So why the need for additional controls? First, because the old verge trims were often installed with little or no consideration given to cold bridging. And second, in the early days of funding for EWI, the emphasis was very much on insulation, cost and payback from savings on energy bills. The focus was on insulating as many properties as possible as cheaply as possible. A basic principle of construction was forgotten. No element of a building operates in isolation. If one element of a construction is failing, it will impact negatively on others.
Before controls were put in place, and before the introduction of the PAS standards, external wall insulation was sometimes being fitted on properties that were already failing with failing roofs, leaking guttering and windows that needed replacing. Most EWI systems will be able to cope with a limited amount of water ingress, but a leaking roof or guttering may compromise even the best fitted EWI systems.
Notwithstanding the above, we also must agree that the interfaces between products and systems are as important as the products and systems themselves. Well-designed interfaces are critical if a building is to resist water ingress and prevent thermal bridging. To this end, RCS design in the new guidance was based on the following principles:
• Water ingress resistance – weather tightness
• Exposure – suitable for all exposure categories
• Redundancy – multiple layers of weathering protection
• Continuity of insulation – elimination of thermal bridges
Routes to Compliance
There are two routes to compliance.
Firstly, an initial survey is carried out to identify whether the existing roofline can use one of the thirteen standard details in the ‘Weathering and Thermal bridge guide (June 2024 edition)’. If such a detail is identified, work can proceed using this detail.
The second route is taken when the survey identifies an RCS need that is not covered in the guide; in this case, the contractor provides the RCS survey to the system designer who, with the Retrofit Designer and RCS fabricator, develops a bespoke solution following the RCS design principles.
In either case, the initial RCS survey should identify any existing issues with the roof / wall interface and detail the remedial works required. (For example: broken slates, missing or ripped felt, cracked or missing cement fillets and the position and thickness of existing roof insulation). Any identified remedial works then need to be completed prior to the EWI system and RCS being applied.
Principles & Considerations
It should be remembered that an EWI system on a retrofit property is not the primary weather protection for the building. The building should be sound and free from moisture ingress prior to its application.
Also, all building systems have the potential to fail, but normally there are warning signs. It is critical that if cracks are observed, render is delaminating or prolonged damp patches are present, they are investigated and the cause rectified. If you saw a damp patch on your bedroom ceiling, you wouldn’t wait until water was dripping on your head to investigate.
And here lies another issue. Many people who have bought their own council property won’t necessarily be able to afford to maintain it to an adequate level. I remember when I was first involved in the application of EWI, the private properties on the estate were mostly the best maintained. Unfortunately, now when I visit sites, where EWI has been applied, it is mainly the private properties that are in disrepair.
It must be realised that external wall insulation is critical to improving the thermal performance of a large proportion of the UK’s housing stock, but this needs to go hand in hand with investment in the maintenance of that stock. Funding policies need to consider this and allow the flexibility to include private properties within schemes.
Decarbonisation of the housing stock is a critical element of achieving net zero. EWI is vital to improving the thermal efficiency of our older solid wall and non-traditionally built properties. But EWI is so much more than just insulation; EWI that is designed and installed correctly will increase the value of a property, extend its life, and improve its aesthetics. Delivered as part of a community scheme, it can also transform a run-down estate to look like a virtually brand-new development. It’s well documented that the environment we live in has a profound effect on our wellbeing. External wall insulation has the potential to improve the lives of individuals and communities as a whole.
It is important that we get it right and continue to develop our products and systems so that they are more effective, easier to apply and generally foolproof. The work done by the industry to develop Roofline Closure Systems is part of a process of continual improvement.
Mitchell Gee is a former chair of the Insulated Render and Cladding Association (INCA) and a former managing director of a leading external wall insulation system provider. He is currently a board member of both INCA and SWIGA. He has 30 years’ experience of working in the sector.
For details of PermaRock’s own roofline closure systems or for associated technical support, please call us on 01509 262924 or email [email protected].