What Is Lead Flashing, and Why Does It Fail?

Lead flashing is the quiet hero of a roof — you rarely notice it until it fails, and then it's usually the reason you've got a leak. Lead flashing seals the joints that ordinary tiles can't cover: where the roof meets a chimney or a wall, and where two slopes form a valley. Fitted properly in the right thickness of lead, it lasts for decades; fitted badly, or smeared over with sealant, it fails fast. It's some of the most skilled work on a roof, and where a lot of leaks begin.

Where you'll find it

• Chimneys — sealing the joint all around the stack where it passes through the roof.
• Abutments — where a roof slope meets a wall, such as an extension against the house.
• Valleys — the channels where two slopes meet and shed a lot of water.
• Around features — dormers, parapets and other details a standard tile can't seal.

Why it fails

Lead moves. It expands in the heat and contracts in the cold, day after day, year after year — and over time that thermal movement can crack it, split it, or work it loose from the mortar joint it's tucked into. Age is the usual culprit on an older roof. But a lot of "failed" lead was never fitted right: a piece too large moves too much and splits, and the wrong code (thickness) wears through sooner. Good leadwork is as much about sizing and dressing as it is about the metal.

Why sealant isn't the answer

When lead goes, the tempting quick fix is a tube of sealant smeared over the gap. It might get you through a dry spell, but it rarely lasts a season — sealant can't cope with the movement lead is designed to handle, and it hides the fault rather than fixing it. The proper repair is fresh lead in the correct code, dressed to shape and fixed and pointed in. It costs more than a smear, and it's the difference between sorting the leak once and chasing it every winter.

How we put it right

We renew failed lead the way it should be done — correct code for the location, cut and dressed to fit, mechanically fixed and pointed in, so it seals and stays sealed. Lead detailing is a big part of why chimney and abutment leaks are the jobs we're called to most, and where our experience shows. Where it helps, we photograph the finished lead by drone so you can see it's been done properly.

Frequently asked questions

What does lead flashing actually do?

It seals the joints where ordinary tiles can't — where the roof meets a chimney, an abutting wall, or in a valley. Shaped and dressed correctly, lead is one of the longest-lasting roofing materials there is.

Why has my lead flashing failed?

Usually age and thermal movement — lead expands and contracts, and over years it can crack, split or lift out of the mortar. Poorly fitted lead (too big a piece, or the wrong code) fails much faster.

Can't you just seal the gap instead of replacing the lead?

Sealant over failed lead is a quick patch that rarely lasts a season. The proper fix is fresh lead in the right code, dressed and fixed and pointed in — it costs more up front and lasts for decades.

What does "code" of lead mean?

Code is the thickness and weight of the lead — higher code is thicker and used where more durability is needed. Using the correct code for the job is a big part of why good lead work lasts.

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Leak around a chimney, wall or valley? That's usually lead — and lead work is our speciality across Hull, Beverley, Hessle and the East Riding. Free fixed written quotes, fully insured. Call 07447 352091.