Technical Guide to Roofline Closure Systems

It has been a long time coming, but roofline closure systems are now approved for PAS projects. This represents a significant milestone for the EWI industry, with updated guidance providing solutions for problematic verge trims. With the endorsement from DESNZ (the Department for Energy Security and Net Zero) and a supporting letter highlighting this development, these systems have been officially approved for PAS retrofit projects. The solutions come after three years of dedicated work by a cross-industry working group. SWIGA has been heavily involved in propagating this solution, and much of the details in this blog are sourced from their guidance.

What were verge trims, and what problems did they cause?

Verge trims are components designed for sealing and protection, especially the junction between the eternal wall insulation and the roofline. In theory, verge trims prevent water ingress but are notoriously prone to failure. Any form of failure also compromises their other function, preventing thermal bridging. By capping the insulation seamlessly, verge trims would eliminate thermal bridges. However, when they failed, they created thermal bridges. They also add durability to the system by preventing damage to the exposed edges of the insulation from weather conditions. Verge trims were more cost-effective than extending the roofline and installing soffits and facias.

What are Roofline Closure Systems?

Roofline closure systems (RCS) have replaced the outdated verge trims after an extended waiting and testing period. Roofline requirements vary significantly depending on the project or property. As such, the RCS has a set of Design Principles that allow specific scenarios to be assessed independently.

Design Principles for RCS

Redundancy of Seals

For eaves with inadequate roof overhang, the protection at 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, with 40 mm for moderate or sheltered exposure and 50 mm for severe or very severe exposure, as defined by the BRE wind-driven rain map in BR262 Thermal Insulation: Avoiding Risks – Appendix A.

Gable-to-Eaves Junctions

These must be created using overlapping, prefabricated units or connectors. Site fabrication is not allowed, although minor on-site trimming is acceptable. Joints between the primary and secondary seals must be staggered by 100 mm. Insulation should be maintained in the corner of the gable wall up to the level of the loft insulation, following the Retrofit Designer’s specifications.

Gable Apexes

Gable apexes should be formed using prefabricated elements. While site-bent flashing can be used, secondary lead or lead-replacement flashing is required over the apex. Site-formed mitre joints with two separate profiles are not permissible.

Connections Between Adjacent Roofline Closure Sections

These connections must include an under- or over-connector extending at least 40 mm on both joint sides. Connectors should be sealed to both metal profile sections (e.g., roofline closure) using proprietary sealing tapes or sealants, which must cover the full width of the trim. Joints between the primary and secondary seals should be staggered by 100 mm.

Use of Lead for Flashing

When using lead for flashing, the maximum length of a single piece should be 1200 mm, and overlaps should follow best practice. Ensure compliance with health and safety regulations outlined in the Control of Lead at Work Regulations 2002 and associated guidance. Lead-replacement flashings should be securely installed as per the manufacturer's recommendations.

Soffit/Roof Overhangs

A minimum overhang of 40 mm (50 mm in high exposure areas) is required. If less, trims or flashings must be embedded into the masonry or below the cement pointing at verges and sealed. Joints between the primary and secondary layers of protection should overlap by at least 100 mm. Sand and cement fillets should be replaced with flexible mortar.

Weathering Protection Details

The installation of weathering protection must be included in the training provided by the EWI system holder for registered EWI installation contractors.

Thermal Continuity

The roof insulation and the insulated roofline closure system must be continuous, ensuring a minimum thermal resistance of 0.6 m²K/W and no thermal bridging.

Compliance

Roofline closure systems not meeting the above requirements are unacceptable for use in funded or private schemes.

Surveys for RCS

A comprehensive property survey is essential for successfully installing Roofline Closure Systems. This evaluation determines the system's suitability and identifies all critical details. Early identification of these factors is important, as various specifics may be required. Precise measurement and documentation of the existing roof overhang are crucial, as they influence the necessary specifications. Additionally, assessing the condition of the substrate is vital to ensure the property can support the installation, particularly for grind-in flashings.

1. Relevant details - Working solution with the existing roof.
2. Existing overhang - Consistency across eaves/verge.
3. Rafter positioning - May need to be boxed in or walked around.
4. Substrate condition - Wherever grinding is needed, ensure the substrate is not damaged.
5. Existing insulation & potential cold bridging - Ensure continuity and minimum thermal resistance of 0.6m²K/W.
6. Corner details - How eaves and verge will meet and the suitable corner profile.
7. Existing features - Architectural and structural features that require specific designs.
8. Ventilation - Roof ventilation must not be obstructed.

A secondary line of protection - the cornerstone of RCS

The Roofline Closure System Principles require two layers of protection across the top of the EWI system. This is achieved with a membrane or flashing, depending on the preference and design specification.

Minimum material requirements

In addition to the design principles, a minimum material specification must be adhered to. Suitable Base material:

• Minimum Aluminium specifications 1050A – Other higher grades are acceptable – 3000/5000.
• Minimum Stainless-Steel specifications 304 – Other higher grades are acceptable – 316.

Minimum thickness:

• 1.2mm aluminium with a +/- 10% tolerance for trim widths up to 160mm.

For trim widths over 160mm or trims to be used in exposed areas, (a minimum 50 mm overhang of 1.5mm aluminium must be considered for added strength and stability.) Coating requirement:

• Polyester Powder-coated aluminium must have 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
• A marine-specified coating should be considered in areas exposed to severe wind-driven rain (Zone 4 of the BRE wind-driven rain map) or directly facing the coast.