The Property

Lead Cappings to Coping Stones – Thornhill, Kirklees

The Old School House in Thornhill, near Dewsbury, is a striking Grade II-listed stone-built property dating back to 1643, during the English Civil War. Originally founded as a boys’ school through a bequest from Reverend Charles Greenwood, the building later evolved into Thornhill Grammar School and subsequently a National School before becoming a private residence in 1974. Architecturally, it is a traditional Yorkshire stone building with substantial masonry walls, stone slate roofing and historic parapet detailing, reflecting the robust craftsmanship of early educational buildings in the region. The property retains impressive period character, including a 55-foot great hall with exposed English oak beams and vaulted ceilings, while its scale and commanding roadside presence make it one of the most distinctive historic buildings on Combs Road.

The property features a traditional stone parapet upstand on a Yorkshire stone slate roof, weathered with lead cover flashings and sandstone coping stones. The raised stone structure projects above the roof slope, while the lead flashing forms a watertight junction between the stone masonry and surrounding stone slates. Common on historic Yorkshire properties, details like this rely on properly formed leadwork and stable stone construction to accommodate movement and protect the roof from water ingress.

Why the Original Leadwork Needed Replacing

This existing leadwork failed due to a combination of aged lead fatigue, movement in the stone parapet, and deterioration of the surrounding stone slate roof. The lead flashing has split and cracked from long-term thermal movement and weathering, while sections of stonework have fractured and become displaced around the junction. Open joints and slipping stone slates have also increased the risk of water ingress into the roof structure below.

Leadwork Standards and Technical Approach

This project was completed using a standards-led approach focused on proper lead detailing, correct material selection and durable support beneath the finished covering.

• BS 6915 informed the design and installation of the fully supported lead sheet covering.
• BS EN 12588 governed the rolled lead sheet material specification.
• Lead Sheet Association guidance informed bay sizing, fixing principles, bossing, welting, corner formation and general good practice.

Preparation for replacing the lead cappings should begin with a full assessment of the stone gable ends to identify any loose masonry, failed mortar joints or damaged sections requiring repair. As this is a historic property, all work should comply with conservation requirements and recognised guidance including BS 6915, BS EN 12588 and Lead Sheet Association recommendations. Existing debris, failed leadwork and defective bedding materials should be carefully removed before cleaning and stabilising the stone surface beneath. New Code 5 lead should then be dry-fitted and formed to suit the profile of the stone parapet, ensuring correct coverage, support and allowance for natural thermal movement prior to final installation.

Specification of Works

Preparation and Removal

• Carefully inspect the stone gable and existing lead cappings to identify failed leadwork, loose masonry and defective mortar joints.
• Erect safe access and protection measures to prevent damage to the stone slate roof and surrounding structure.
• Carefully strip out existing lead cappings, flashings and defective fixings without damaging adjacent stonework.
• Remove failed bedding materials, debris and biological growth from the top of the stone parapet and abutment areas.
• Inspect and prepare the exposed substrate and stonework ready for repair and installation of the new lead cappings.

Substrate and Support

• Repair and stabilise defective stonework, loose coping sections and failed mortar joints along the parapet.
• Form a clean, level and fully supported surface to receive the new lead cappings.
• Install appropriate timber support pieces or treated backing where required to improve fixing and detailing.
• Ensure all supporting surfaces are dry, secure and prepared in accordance with Lead Sheet Association guidance prior to installation.

Leadwork Installation

• Measure and mark the new Code 5 lead cappings to suit the full length and profile of the stone parapet.
• Cut and shape the lead sheets using leadworking tools to form neat folds, drips and corner details.
• Dry-fit the lead sections to check alignment, coverage and correct overhangs before final fixing.
• Apply a suitable lime-based bedding mortar to provide support beneath the lead cappings where required.
• Install the new lead cappings with correctly formed laps and allowance for natural thermal movement.
• Secure the lead using non-corrosive clips and fixings in accordance with Lead Sheet Association guidance.
• Dress and boss the lead neatly over the stone edges to achieve a watertight and traditional finish.
• Complete all joints, trims and edge details to ensure effective weather protection and drainage from the parapet.

Finishing and Protection

• Patination oil applied to all exposed lead immediately after completion.
• Surrounding surfaces cleaned down.
• Completed detail checked for finish, continuity and weathering performance.

The Materials

This project used a straightforward but important group of materials, each chosen for a clear purpose within the bay roof build-up.

• Code 5 lead
• Copper ringshank nails
• Lead sealant
• Patination oil

If you are trying to understand which code of lead is right for a similar detail, our shoppable lead chart is a useful starting point. For broader product learning, see The Lead Handbook and our lead roofing guides.