On Wednesday 14th August, the Department for Energy Security and Net Zero (DESNZ) issued a letter announcing its formal approval for the use of roofline closure systems on PAS-compliant external wall insulation schemes. In this article, Dr Jeremy Richings – Technical Director at PermaRock and a member of the working group that developed the associated Design Principles – explains what this means for housing managers and installers.
The decision by DESNZ resolves an issue that has been keenly watched and discussed by the retrofit industry for a number of years. Until this month’s announcement, Roofline Closure Systems could not be used on publicly-funded projects delivered to the PAS 2030 & PAS 2035 standards. The only permissible way to protect newly installed EWI systems was to extend the roofline at the eaves and verges. As we discussed in a previous article, this was not always practicable and the prohibition of ‘verge trims’ meant that many homes had to be excluded from badly-needed decarbonisation programmes.
Now, however, the official guidance has changed, and it introduces the opportunity to deliver retrofit works to a much wider range of properties, yielding benefits for residents and communities alike.
However, the guidance emphasises that Roofline Closure Systems, even when properly designed and installed, should only be used when roofline extension is not a viable option. (Cost-savings alone are not considered to be sufficient reason to consider roofline extensions to be non-viable.) Nevertheless, in view of the number of mixed-tenure terraced properties and homes with other restrictive features, it seems likely that Roofline Closure Systems will become increasingly visible in Britain’s streetscapes.
More detals are provided in our new Roofline Closure Systems brochure, which can be downloaded from our Technical Hub, here on the PermaRock website.
New Design Principles
The updated Weathering Guide (“External Wall Insulation Specification for Weathering and Thermal Bridge Control Guide August 2024”) sets out ways in which roofline closure systems can be incorporated into PAS-compliant retrofit designs.
The first involves using one of 13 standard details provided in the Weathering Guide itself (a copy of which can be downloaded via the Technical Hub.)
The second entails applying a set of core Design Principles, which have been developed by a working group set up by the National Insulation Association (NIA), the Solid Wall Insulation Guarantee Agency (SWIGA), and the Insulated Render and Cladding Association (INCA).
The new Design Principles have been reviewed and accepted by the Retrofit Standards Task Group, DESNZ and Trustmark. These, and the accompanying materials specifications, enable bespoke, compliant designs to be developed to suit individual projects and archetypes, while also mitigating thermal bridging and providing enhanced weathering resistance.
The working group has also produced an accompanying Process Map to help designers to determine whether standard details are appropriate for use.
The Design Principles are not prescriptive and they allow designers to develop appropriate solutions based on project requirements and property-by-property surveys. Typically conducted by the Retrofit Assessor, such surveys should consider important factors including (but not limited to):
- The design and condition of the substrate
- The design of the existing roofline system(s)
- The size of the overhang
- Any architectural features that may preclude the use of roofline closure profiles
- The need to maintain the integrity of any existing insulation
- The risks of cold-bridging
- The need for adequate ventilation
- Corner details
- Aesthetic / planning concerns
Working with the EWI System Designer, the Retrofit Designer will then develop a design based on the Process Map. This, along with all other design elements, must be signed off by the Retrofit Coordinator.
A key requirement is that designs for Roofline Closure Systems must feature two layers of weather protection over the top of the EWI system. In addition to the roofline closure profile itself, which will be made of polyester powder-coated aluminium or stainless steel, the secondary protection will typically comprise either additional metal flashing or a weatherproof membrane.
Designs will be developed in collaboration with the system supplier, which will have developed products to suit a wide range of designs, archetypes and environments.
Profile Base Material – Minimum Specification
- Aluminium 1050A or better (3000/5000) / with a minimum thickness of 1.2 mm +/- 10% for profile widths up to 160 mm; and 1.5 mm for profiles in exposed locations where a minimum 50 mm projection from the finished render face is required.
- Stainless Steel 304 or better (316).
Coating – Minium Specification
- Polyester powder coated (PPC) aluminium: a minimum coating thickness of 40 microns to BS or Qualicoat standards, and powder coaters must be BS or Qualicoat approved applicators.
- Pre-coated aluminium must be polyester-coated on both sides and the thickness must conform to EN 13523-1.
- In areas exposed to severe wind driven rain (Zone 4 of BRE wind driven rain map) or directly facing the coast, a marine specification coating should be considered.
Next Stages
Roofline Closure Systems can now be incorporated into designs for PAS-compliant decarbonisation schemes, subject to the caveats noted above.
PermaRock’s Technical Support team is available to help clients and specifiers by providing project advice, product information, and support with drawings and detailing. Please get in touch via our Contact page, call us on +44 (0) 1509 262924, or email: [email protected].