Lead flashing is one of the most critical components of a roof, yet most homeowners only become aware of it when it fails. If you have ever had water coming in around a chimney stack, at the junction between a roof slope and a wall, or where two roof surfaces meet, there is a very good chance failed lead flashing was involved. This guide explains what lead flashing is, why it is used, and what happens when it starts to break down.
What Is Lead Flashing?
Lead flashing is sheet lead — typically code 3, 4, or 5 — that is shaped and fitted to seal the junctions between different roof surfaces and between the roof covering and vertical walls. Wherever a roof meets a chimney, a parapet wall, a dormer, or an adjoining structure, there is a vulnerable joint that needs sealing against wind-driven rain. That seal is almost always provided by lead.
The most common types you will encounter on residential properties are step flashings (running up a chimney or abutment wall in overlapping steps that follow the course of the tiles), cover flashings (a continuous strip that overlaps the top of the step flashings), and apron flashings (a single piece that seals the front face of a chimney at the base). Valleys — the internal angles where two roof slopes meet — are also frequently lined in lead.
Why Lead and Not Something Else?
Lead has been used on British roofs for centuries for good reason. It is extremely malleable, which means it can be worked to follow complex shapes and profiles. It expands and contracts with temperature changes without cracking. It is highly resistant to corrosion in the atmosphere and against most building materials. And it has an exceptional service life — a correctly installed Code 5 or Code 6 lead flashing, installed to Lead Sheet Association (LSA) standards, can last 60 years or more.
Modern alternatives including EPDM strips and self-adhesive flashings are used in some situations, particularly on flat roofs or in areas of lower exposure, but for pitched roofs on period properties, properly dressed lead remains the correct and most durable solution.
Common Lead Flashing Failures
- ✓Thermal cracking — lead that has been installed in sections longer than the LSA recommends will eventually crack as it expands and contracts with temperature changes.
- ✓Lifting at the chase — lead is typically tucked into a chase cut into the mortar joint of a brick wall. If the mortar pointing deteriorates, the lead lifts and water can track behind it.
- ✓Corrosion from incompatible materials — lead in direct contact with certain timbers (particularly oak) or with certain types of mortar can suffer accelerated corrosion.
- ✓Poor original installation — lead that has been cut too short, installed without correct drips or expansion allowances, or pointed with hard cement mortar rather than correct leadwork sealant will fail prematurely.
- ✓Storm damage — lead that is correctly dressed is very robust, but extreme uplift in storms can displace flashings that were already marginal.
All lead flashing work carried out by Kirby's BPM is installed to Lead Sheet Association (LSA) standards, which specify the correct code of lead for each application, maximum bay lengths to allow for thermal movement, correct lap dimensions, and appropriate fixing methods.
Repair or Replace?
In many cases, a lifting or open-jointed flashing can be re-dressed and re-pointed without full replacement. If the lead itself is sound but has simply worked loose from the chase, we can re-fix it correctly. Where the lead has cracked, torn, or corroded, or where the original installation was too short or incorrectly detailed, replacement is the right approach. Our lead flashing service covers both repair and full replacement — we assess each situation on its merits and explain the options clearly before any work is priced.