What is stepped flashing on a chimney?

Where a vertical brick stack meets a sloping roof, the gap between them runs at an angle. A flat strip of lead cannot seal it, so the lead is cut into a staircase pattern, one step for each course of bricks as the stack rises from the roof. The upper edge of every step goes into the brickwork. The lower part lies flat across the roof covering and overlaps it, so water runs on to the tiles and away.

On a tiled or slated roof the steps usually work alongside soakers. A soaker is an L-shaped lead tab, one for each course of tiles, that slides beneath the tiles and bends up the brick face. The soakers carry water off the roof surface, and the stepped flashing covers the joint above them. Together they make a tight edge that no single piece of lead could manage.

The top edge of each step sits in a slot sawn into the bed joint of the bricks (the chase). It is held with small lead wedges and the joint is pointed up again over it. That gives a mechanical hold that does not depend on glue. Because the lead sits inside the wall, rain running down the brickwork drops over the top of it instead of behind.

Sealant smeared along the face of the brickwork is a different thing. It can hold for a while as a stopgap, but it sits on the surface, moves with the weather and splits at the edges. When a stack that was "done with mastic" starts leaking again, the cure is usually proper lead set into the joints. A good run also looks tidy, with level steps, even laps and crisp pointing, and that neatness is a sign it has been fixed with care.

Sheet lead is sold in numbered codes, each one a thickness. In Royston Lead's cast-lead brochure, code 4 (1.80 mm) is listed for soakers, flashings and valleys, while codes 5 and 6 (2.24 mm and 2.65 mm) are listed for flashings and heavier gutters. A thicker code is stiffer and takes longer to work into the steps, and the choice depends on the exposure of the stack and what the existing work uses. Our guide to lead codes for chimney flashing walks through the options.

Lead has a long working life when it is fitted well. MyJobQuote puts the life of chimney flashing at over 80 years, which is a typical life and no guarantee, and assumes the lead is fixed and lapped properly. In our experience, poor fixing, not the metal itself, is usually what lets go first.

When we renew a run, the code follows the old work unless the roof gives a reason to change it, and you are told which code goes on.

From the ground you may spot lead curling off the brickwork, a step that has slipped, or cement filling the gap where lead should be. Closer up, the mortar along the chase crumbles, the wedges fall out and the top edge of the lead stands proud of the wall. Indoors, look for a brown mark on the breast or the ceiling close to the stack, often after driving rain.

Do not assume the steps are always the culprit. Water may come in at the front apron, the back gutter, the flaunching or the brickwork itself. That is why we survey every part of the stack and photograph each fault, then tell you which parts need work and which are sound.

For the other places to check, our page on a chimney leaking in rain runs through them, and the chimney repairs hub gives the whole picture.

MyJobQuote (last updated 22 September 2026) gives £150 to £250 for patching chimney lead and a full replacement at at £350 to £460 without scaffold, or £700 to £920 with scaffold. Those are typical UK ranges. What moves a figure is the size of the stack, whether it has more than one side to flash, the access and how much old lead and pointing has to come out.

Stepped flashing is normally priced together with the rest of the stack's leadwork, because the front apron and back gutter are at the same height and are best done in the same visit. For your own roof, the survey comes first and the price reaches you in writing, as one sum. For more on cost see our page on chimney lead flashing cost.

A single lifted step can sometimes be re-dressed and re-wedged, and a small tear can be patched. But if the lead is thin, cracked in several spots, or has been stuck down with sealant over many years, a new run outlasts a string of patches. The smaller repair is recommended whenever it will hold, with pictures of the lead so the reason is clear.

A full renewal means lifting the soakers along the side, stripping the old steps, raking out the chase and fitting new lead from the bottom up. Then the joints are pointed and the tiles are put back. The time needed varies with the access and with how many sides of the stack need flashing. If the stack is in poor condition, the pointing and brickwork may need attention at the same time.