What Is a Lead Apron Flashing?

Water runs down a roof slope until something stops it. A chimney stack, a dormer front, a skylight or the face of a taller wall all do exactly that, and the joint between that obstacle and the tiles is where leaks begin. The apron is the piece of lead on the low side, where the greatest volume of water arrives. A flashing is simply a strip of waterproof metal that bridges a joint, and the apron is the one lying across the bottom of the obstacle.

The top edge goes into the upright surface, usually a groove cut into brickwork called a chase, and is held there with lead wedges and then sealed. The sheet then drops down the brickwork, bends over the corner and lies flat on the tiles, often with its lower edge shaped to follow the profile of the covering. Water meeting the joint passes over the lead, never behind it.

The side pieces are separate flashings, and the upslope side has its own tray or gutter. The apron is the part you notice because it sits right in view below the chimney.

A good apron is one piece of lead, cut to the width of the obstacle with enough spare at each end to join the side flashings. Lead is soft, so it is dressed by hand into the shape of the surface below, using a dresser or a bossing stick, rather than hammered flat. Detail around a ridged concrete tile needs more dressing than a flat slate, because the gaps under the lead are bridged by shaping, not by filling them with sealant.

The upper edge is turned into the chase and wedged every few hundred millimetres, then closed with mortar, or with a flexible sealant where the brick suits it. On the roof the lead is held by its own weight and, where it is long, by clips along the lower edge, so wind cannot lift it. Nails through the visible face are a fault, because rain finds the holes.

The weight of the sheet is called its code. Royston Lead's brochure lists Code 4 to Code 6 among its flashing weights, and our guide to what code lead for flashing explains the choice.

Most apron leaks come from a short list of faults. The wedges loosen and the lead slumps out of the chase. The mortar or sealant along the top edge cracks and lets water behind. The lower edge lifts in strong wind because it was not clipped. Or the lead splits at the corner fold, where a stiff sheet has been bent too tightly and tired by the daily swing between warm afternoons and cold nights.

Sealant smeared along the top edge is a clue that someone has tried a quick fix. It can buy a few months, but if the chase itself has crumbled it will not hold. A tiled roof where the lower edge has been bent over a gap in the tiles, instead of being shaped to them, will also let wind-driven rain blow under it.

Inside, the signs are brown marks on the bedroom ceiling beside the chimney breast, or damp timber in the loft around the stack. Our answer on whether lead flashing can be repaired shows when a patch will do.

Where the sheet is healthy and just the wedges or pointing have given up, repair does the job: rake out the old mortar, re-wedge, repoint and check the corners. If the sheet is split, thin or buckled, a new apron is the lasting answer, and it is fitted together with new side flashings so the joints line up.

As a national guide, Checkatrade's June 2026 repair table puts lead flashing repair at £50 to £70 per metre, and stepped flashing at £80 to £120 per metre in Code 5. Chimney flashing repairs run from £250 to £1,000 in its April 2026 table. Access moves the figure most, because reaching a stack above a first-floor roofline normally means a tower or scaffold. Find out whether the figure you are given has VAT and scaffold built into it.

We look before we price. The survey includes photos of the apron, the chase and the tiles beneath, and the price you receive in writing is a single total. Ask for pictures of the lower edge too, which show at a glance whether the lead was shaped to the tiles. To understand the other flashings round the stack, see step flashing and cover flashing, or the main lead work page.