Flashing

Flashing is a waterproofing material — usually thin sheets or strips of metal — installed wherever a roof meets a wall, chimney, skylight, vent pipe, or another roof section. Its job is to channel rainwater away from these vulnerable joints and prevent it from seeping into the building structure.

Types of flashing

• Lead flashing — the traditional choice in the UK, very durable and long-lasting (50+ years), but heavy and more expensive
• Aluminium flashing — lightweight, rust-resistant, commonly used in the US
• Zinc and copper — premium options that develop a natural patina over time
• Self-adhesive bitumen strips — a budget option for minor repairs, though not as durable as metal
• EPDM rubber — flexible, good for flat roofs and awkward angles

Where flashing is used

• Where a sloped roof meets a wall (step flashing)
• Around chimneys (chimney flashing)
• Around skylights and roof windows
• In roof valleys where two slopes meet (valley flashing)
• Around vent pipes and soil stacks
• Where an extension roof meets the existing house

Why flashing matters in a renovation

If your renovation involves any roof work — adding a dormer, building an extension, installing a skylight, or simply replacing old roofing — proper flashing is critical. Failed or poorly installed flashing is one of the most common causes of roof leaks.

• Extensions — the junction where a new extension meets the existing building is one of the most leak-prone areas and relies entirely on good flashing
• Chimney work — old lead flashing around chimneys often cracks or separates, causing damp patches on internal walls
• Building regulations — flashing installations must meet local building standards

Practical tip

When your contractor provides a quotation, check that flashing is explicitly mentioned for every junction. It is sometimes overlooked in quotes but is essential for a watertight finish. Ask what material will be used and whether any existing flashing will be reused or replaced.