The Property

Large Loft Dormer Lead Roof Covering

This project involved the installation of a new lead roof covering to a large loft dormer. Large dormers require careful detailing because they often include flat or low-pitched roof areas, vertical cheeks, front aprons, flashings, abutments and exposed perimeter edges.

Unlike smaller dormers, a large loft dormer can include several separate lead bays. Each bay must be set out correctly to allow the lead to expand and contract naturally without splitting, buckling or placing stress on fixings.

The aim of this project was to provide a durable, fully supported lead dormer roof using traditional leadworking techniques, correct substrate preparation and suitable movement details.

Why Large Dormers Require Specialist Leadwork

Large dormer roofs are exposed to wind, rain, temperature changes and concentrated water run-off from adjacent roof areas. Poor detailing can lead to ponding, split lead, failed flashings, water ingress and premature deterioration of the supporting timber structure.

Lead is particularly well suited to dormer construction because it can be formed around complex roof shapes, dressed into junctions and detailed to suit traditional or modern properties. However, it must be installed correctly to perform as intended.

Leadwork Standards and Technical Approach

This dormer roof was designed around recognised leadwork principles, with careful consideration given to bay sizing, support, ventilation, fixing and thermal movement.

• BS 6915 informed the installation of the fully supported lead sheet covering.
• BS EN 12588 governed the rolled lead sheet material specification.
• Lead Sheet Association guidance informed movement allowance, bay sizing, fixing, welding, welting and detailing.

The key principle was to allow the lead covering to move naturally while maintaining secure weather protection. This required correct substrate preparation, timber roll formation, properly fixed clips and carefully formed weathering details.

Specification of Works

Preparation and Removal

• Safe access established to the dormer roof area.
• Existing coverings and defective weathering details removed where required.
• Dormer structure inspected for condition, falls and suitability for new leadwork.
• Adjoining roof coverings, abutments and flashings checked prior to installation.
• Work area prepared for new substrate and lead roof covering.

Substrate and Support

• New 18mm exterior-grade plywood decking installed to provide continuous support.
• Timber rolls formed to divide the dormer roof into suitable lead bays.
• Building paper / lead underlay installed beneath the lead sheet.
• Falls and perimeter details prepared to encourage effective water run-off.

Leadwork Installation

• New dormer roof covering formed using Code 5 rolled lead sheet.
• Lead bays set out to suit the size and geometry of the dormer.
• Timber roll details dressed neatly to control movement and create traditional bay divisions.
• Welted edges formed to improve strength and weathering performance.
• Lead flashings integrated into adjoining roof slopes and vertical abutments.
• Perimeter clips installed using suitable non-ferrous fixings.
• Expansion details incorporated where required to accommodate thermal movement.
• Completed leadwork checked for laps, cover, falls and weathering continuity.

Finishing and Protection

• Patination oil applied immediately after installation.
• All joints, clips, flashings and roll details inspected.
• Completed dormer roof checked for finish quality and weathering performance.

The Materials

• Code 5 lead
• 18mm exterior-grade plywood
• Timber rolls / king roll details
• Building paper / lead underlay
• Copper clips and non-ferrous fixings
• Patination oil

The materials selected for this project were chosen to provide a robust, fully supported and traditional lead dormer roof covering. Code 5 lead was used to provide suitable durability, while timber rolls and correctly formed bay divisions helped manage movement across the larger dormer area.