The Property

Chimney Flashing – Traditional Leadwork Detail

This project involved the installation of new lead flashings around a traditional brick chimney stack. The chimney rises through a clay tiled roof, creating one of the most vulnerable roof junctions on the property.

Chimney flashings are important because they create a watertight junction between the roof covering and the masonry. Since a chimney interrupts the natural slope of the roof, rainwater must be directed safely around the stack and back onto the roof covering below.

The completed detail included apron flashings, stepped side flashings, counter flashings and weathering details formed to suit the roof pitch, tile profile and brickwork courses.

Why Chimney Flashings Need Replacing

Chimney flashings often fail because of age, poor previous repairs, failed mortar joints, split lead, inadequate laps or movement-related fatigue. Once the flashing begins to fail, water can enter behind the lead and track into the roof structure.

In many cases, chimney leaks are not caused by the chimney stack alone, but by the junction between the stack, tiles, back gutter, apron and side flashings. For that reason, proper replacement needs to address the full chimney weathering detail rather than relying on temporary sealant repairs.

Leadwork Standards and Technical Approach

From the outset, we focused on movement, durability, neatness and long-term weathering performance.

• BS 6915 informed the design and installation of the lead sheet flashings.
• BS EN 12588 governed the rolled lead sheet material specification.
• Lead Sheet Association guidance informed laps, chase depths, cover flashings, apron details and movement control.

In practice, that meant selecting the correct lead code, forming separate flashing pieces, chasing the lead into sound mortar joints and allowing the leadwork to move naturally without splitting or pulling away from the chimney stack.

Specification of Works

Preparation and Removal

• Carefully stripped back tiles around the chimney stack where required.
• Prepared the chimney abutments and surrounding roof covering for new leadwork.
• Raked out suitable mortar joints to receive new stepped and cover flashings.
• Checked the front apron, side abutments and back gutter positions before installation began.

Substrate and Support

• Prepared support beneath apron and back gutter details where required.
• Checked tile alignment around the chimney stack.
• Set out lead flashings to suit the roof pitch, tile profile and brick courses.

Leadwork Installation

• Installed new Code 5 lead apron flashing to the front of the chimney stack.
• Formed stepped lead flashings to both sides of the chimney.
• Chased lead flashings into the brick mortar joints.
• Secured flashings using lead wedges at suitable centres.
• Formed counter flashings to overlap and protect the stepped flashings below.
• Formed back gutter or saddle flashing to the upslope side of the chimney where required.
• Used lead bossing and dressing to shape the flashings neatly around the tiled roof covering.
• Pointed or sealed chases using suitable lead-compatible materials.

Finishing and Protection

• Re-laid surrounding roof tiles neatly against the completed flashings.
• Checked all laps, joints and chases for continuity and water run-off.
• Applied patination oil to all newly completed leadwork.

The Materials

For this project, we selected traditional leadwork materials suited to chimney flashing details, tiled roof junctions and long-term weathering performance.

• Code 4 lead for stepped and cover flashings where appropriate
• Code 5 lead for apron and back gutter details
• Lead wedges and suitable fixings
• Lead-compatible pointing mortar or sealant
• Patination oil
• Timber support beneath apron and back gutter details where required

If you are comparing materials for a similar chimney flashing detail, our shoppable lead chart is a helpful place to start. In addition, you can explore broader product guidance through The Lead Handbook and our lead roofing guides.