Since our previous update in January 2024, considerable progress has been made on finalising the Design Principles for Roofline Closure Systems and relevant supporting documents. In this article, Dr Jeremy Richings – Technical Director at PermaRock and a member of the working group that developed the design principles – explains the project’s current status, and how its formal approval will affect the industry.
In recent weeks, the EWI industry working group set up by members of the National Insulation Association (NIA), the Solid Wall Insulation Guarantee Agency (SWIGA), and the Insulated Render and Cladding Association (INCA), have had a series of productive meetings with Trustmark and DESNZ. As a result, it has secured official approval for the roofline closure systems project and we can now progress to the delivery stage.
DESNZ has not yet made any formal announcement, but a statement is expected within a matter of weeks. In the meantime, we can begin the process of informing the industry and explaining the processes involved.
Speaking on behalf of SWIGA, its Executive Director Andrew Champ said:
“SWIGA is pleased that the extensive work by industry in developing a robust set of solutions for the EWI system-to-roof interface (known as Roofline Closure Systems) has now been accepted by Trustmark and DESNZ and that we can move to the training and communication phase. A dedicated group put thousands of hours into the project over two and a half years to bring this to a positive conclusion. We thank them for their dedication, perseverance and expert input.”
The context for this announcement is well known. Table B4-I1 b) ii of PAS2030:2023 currently precludes the use of metal or plastic cappings and trims (“verge trims”) at interfaces with roofs at eaves as a means of protecting newly installed external wall insulation systems; that is, unless these are detailed within the document External Wall Insulation Specification for Weathering and Thermal Bridge Control Guide 2022 (‘Weathering Guide’). Therefore, until such time as the revised Weathering Guide is formally released, extending the roofline remains the only option.
New Principles
The new Design Principles and an updated Weathering Guide (“External Wall Insulation Specification For Weathering And Thermal Bridge Control Guide 2022”) set out ways in which roofline closure systems can properly be incorporated into retrofit designs – i.e., in ways that maintain compliance with the PAS standards. Importantly, however, extending the roofline at eaves and verges will remain the preferred option. Cost-savings will not generally be considered sufficient reason to choose roofline closure systems in preference to roof extension.
In short, roofline closure systems should only be specified when extending roof verges is impractical or impossible. (An example would be when installing external wall insulation to a small number of mid-terrace properties; in such cases, extending the roofs of individual houses would present both technical and aesthetic challenges, so a roofline closure system could be the more appropriate solution.)
Proper Use of Roofline Closure Systems
Through discussions with government, BSI, The Retrofit Standards Task Group and Trustmark, the working group has developed a process map that Retrofit Coordinators and Designers should use to determine when it might be appropriate to specify a roofline closure system. The following is an informal summary of that process and the accompanying design principles. It should not be regarded as the final approved wording.
Initial Survey
As part of any retrofit scheme, it is a requirement that the existing building is surveyed by a suitably competent person to establish the condition of the existing structure and its suitability to be retrofitted with whatever measures are under consideration (e.g. replacement windows, installation of ASHP, installation of solar thermal/PV, application of EWI, replacement roofing, etc.). These initial surveys are usually conducted by the Retrofit Assessor in conjunction with the Retrofit Designer, Retrofit Installer, and relevant specialist suppliers (e.g. EWI system provider, roofing contractor, etc.).
The Retrofit Designer will develop a design based on the Process Map. This, along with all other design elements, has to be signed off by the Retrofit Coordinator. The Retrofit Designer will work with the system designer who will have their own standard details based on the designs in the Weathering Guide (“External Wall Insulation Specification for Weathering and Thermal Bridge Control Guide 2022”) and who has the skills to develop new solutions that meet the Design Principles (see below).
Note that qualifications /competencies of the Retrofit Assessor, Retrofit Designer and Retrofit Coordinator are set out in the various PAS documents. EWI system designers will have preferred installers for their own system designs.
Suitability for Roofline Closure Systems
The suitability (or otherwise) of roofline closure systems must be determined by the Retrofit Designer. If a roofline can be extended, it is expected that the Retrofit Designer will provide a design for this approach. If, during the survey, it is identified that extending the roofline is neither feasible nor practicable, then a roofline closure system can be considered for use.
It should also be borne in mind that the client and/or its local Planning Department may object to the use of roofline closure systems and insist that rooflines be extended (or vice versa).
Repairs Prior to Installation of Roofline Closure Systems
The retrofit building inspection will pick up issues with all areas of the existing fabric: EWI systems cannot be installed onto walls that are not structurally sound or stable, and therefore appropriate repairs to the substrate must be carried out and completed prior to the installation of the EWI system or roofline closure system.
As with all repairs and retrofit installation measures, it is the responsibility of the Retrofit Installer to ensure that these are undertaken to the required standards and in accordance with the specification and Retrofit Design. Retrofit Coordinators should be encouraged to visit the sites to make inspections of the on-going works (i.e. before completion) to ensure that works are being carried out as per the Retrofit Design.
Design Principles for Roofline Closure Systems
A set of Design Principles has been developed as a support tool for the roof closure systems and these will be included within the revised External Wall Insulation Specification for Weathering and Thermal Bridge Control Guide.
It is recognised that the documented details are not exhaustive. These Design Principles are designed to be used to develop new roofline closure system solutions that comply with the PAS 2030 & PAS 2035 standards. They do not define specific designs. Rather, they define criteria with which Retrofit Designs must comply. Designers will therefore have the flexibility to develop solutions to suit individual projects and property archetypes.
The Design Principles are:
1. Redundancy of Seals. At least two lines of weathering protection are required. Sealants shall not be employed to provide the primary barrier to water penetration. The additional redundancy can be achieved with an additional trim or suitable membrane. All joints must have a double seal to comply with the PAS requirements.
At eaves with insufficient roof overhang: Protection afforded to the top of the EWI system must include a secondary waterproof membrane and/or flashing that tucks under the existing sarking felt. The overhang must be appropriate for the exposure zone: 40 mm for moderate or sheltered exposure; 50 mm for severe or very severe exposure (based on the BRE wind driven rain map in BR262 Thermal Insulation: Avoiding Risks – Appendix A: WP2 / (publishing.service.gov.uk).)
2. Gable-to-eaves junctions must be achieved with overlapping, prefabricated units/connectors: Site fabrication is not permissible, though minor on-site trimming is permissible. Any joints between the primary and secondary seal must be staggered by 100 mm. Insulation to be maintained in the corner of the gable wall up to the level of loft insulation as per Retrofit Designer requirements.
3. Gable apexes must be formed using prefabricated elements: Site-bent flashing can be utilised; however, secondary lead/lead replacement flashing is required over the apex. Site-formed mitre joints using two separate profiles are not permissible.
4. Connections between adjacent sections of roof closure systems, etc., must incorporate an under-or over-connector that extends min. 40 mm on each side of the joint. Connectors must be sealed to both sections of the metal profile (roof closure, etc.) using proprietary sealing tapes or proprietary sealants that must extend for the full width of the trim. Any joints between the primary and secondary seal must be staggered by 100 mm.
5. If using lead as a solution, the maximum length in a single piece should be 1200 mm and overlaps should follow best practice. Ensure health and safety requirements are complied with – Control of Lead at Work (Third edition) - Control of Lead at Work Regulations 2002 Approved Code of Practice and Guidance (hse.gov.uk). If lead replacement flashings are used, these should be securely fixed in accordance with the manufacturer’s recommendations.
6. If existing soffit/roof overhangs are ≤ 40 mm (50 mm for severe/very severe exposure to wind-driven rain) then trims/flashings must be embedded into the masonry, or below the cement pointing at verges and sealed. Any joints between a primary and secondary layer of redundancy must be overlapped by a minimum 100 mm. The sand and cement fillet should be replaced with a suitable flexible mortar.
7. The installation of the weathering protection details must be separately included within the EWI system holder training that is provided to registered EWI installation contractors.
8. In all cases, there should be continuity of the roof insulation and the insulated roofline closure solution to provide a minimum thermal resistance of 0.6m2K/W (and ensure no thermal bridging).
9. Roofline closure details that do not meet the requirements above are not acceptable for use with any funded or private schemes and are deemed non-compliant with the requirements of PAS2030 & PAS2035.
Minimum Material Specification for Roofline Closure Systems
In addition to setting out the Design Principles outlined above, the working group has established minimum specification requirements for metal components that can be used within Roofline Closure Systems.
Suitable base materials
- Aluminium: Grade 1050A or higher (e.g. 3000/5000 series alloys).
- Stainless steel: Type 304 or other/higher grades (e.g. 316).
Minimum thickness
- Aluminium: minimum 1.2 mm for metal profiles/trims with widths up to 160 mm. For ≥ 160 mm, and profiles/trims trims to be used in severe/very severe exposure locations exposed areas (where a minimum 50 mm projection from the finished render face is required), min. 1.5 mm.
Coating requirement
- Polyester powder coated (PPC) aluminium: minimum coating thickness of 40 microns to BS or Qualicoat standards
- 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
As noted earlier, an official announcement is expected shortly from DESNZ who will formally notify industry stakeholders including Trustmark, Retrofit Academy, Certification bodies, Local Authorities, etc. In the meantime, system designers / manufacturers are encouraged to prepare their training materials, supporting designs and literature. Clients, Retrofit Coordinators and Retrofit Designers are likewise encouraged to review the updated documents as soon as they become available. They can be found using the links below:
- PAS2035: 2023: (from BSI Group website)
- PAS2030: 2023: (from BSI Group website)
- Weathering Guide: (TBC: the new version of the Weathering Guide will be posted on the SWIGA, NIA and INCA websites as soon as DESNZ makes its formal announcement.)
Technical Support
PermaRock’s Technical Support team is available to support clients and specifiers with advice and further information. Please get in touch via our Contact page, call us on +44 (0) 1509 262924, or email: technical@permarock.com.