Lead tells you a great deal about its own condition if you know what you are looking at. Most of it is visible from the ground with a zoom lens.
Worth starting here, because a lot of people worry about lead that is doing perfectly well.
New lead is bright silver. Within weeks it develops a grey patina - a thin layer of lead carbonate that forms on the surface and then protects the metal underneath. That layer is why lead lasts as long as it does, and a stack whose flashing is a uniform dull grey is a stack whose flashing is fine.
Sound lead also sits flat. It follows the shape of what it covers, its top edge disappears into a neat pointed line in the brickwork, and its bottom edge lies down over the tiles or slates rather than standing away from them.
A dark open line where the lead meets the brickwork. The top edge of a cover flashing is turned into a chase raked out of a mortar joint, wedged and pointed. When the pointing erodes you get a visible shadow line, and once the wedges can move the whole edge is on borrowed time. This is the commonest visible sign and it is easy to see from the ground.
The lead standing away from the wall. It has come out of its chase entirely. Water now runs straight down the brickwork and behind the flashing.
A split running along a fold. Lead fails where it bends, because that is where thermal movement concentrates. A crack across a flat area is unusual; a crack along the line where the sheet turns is the classic.
A curled or lifted bottom edge. The free edge should lie down. If it is standing proud, the wind has been getting under it and will keep doing so.
A sagging or bellied apron. The piece below the stack should follow the roof. If it has dropped in the middle it has lost its support or its fixing.
Nothing there at all. A triangular fillet of grey mortar where a stepped line of lead should be is a cement fillet, and it is a defect from the day it was applied rather than a failure.
Anything black, silver-taped or rubbery. Sealant, bitumen paint or flashing tape over a junction. That is a previous repair that has bought time, and it will have to come off before a proper one can be done.
Two things get mistaken for lead failure and neither is.
White streaking down the tiles below new lead. That is patination bloom - lead carbonate washing off the surface of fresh lead before the patina has stabilised. It is cosmetic, it means patination oil was not applied when the lead went on, and it weathers off. It says something about how carefully the job was done and nothing about whether the lead works.
A blotchy, uneven grey. Also normal. Lead patinates unevenly depending on how much water runs over each part.
What is not normal is white powdery corrosion in a damp, poorly ventilated position, or lead that has gone thin and papery where water has run over the same line for decades. Both are genuine, and both are usually found on lead in a gutter or a valley rather than on a vertical flashing.
On the railway terraces the stacks are tall, frequently shared between two houses and often the tallest thing on the street.
That matters for two reasons. Tall stacks take more wind and more driving rain than anything else on the building, so their lead works harder. And a shared stack means the lead you can see from your own garden may be the half that belongs to the house next door - so a checklist done from your side can miss the failure entirely.
It is worth walking to the front and looking at both faces, and worth asking the neighbour whether they have had damp too. On a party stack it is common for two households to have separately paid roofers for years without comparing notes.
Stand as far back as you can get with a clear view, with the sun behind you rather than in front. Take a photograph at maximum zoom and study the image rather than squinting upward.
Look at the lines first - the top edge, the fold lines, the bottom edge. Failure is almost always on a line.
Do both visible faces of the stack, and if the roof is visible from a neighbouring upstairs window or from higher ground, use that view for the back gutter, which is the one component this method cannot otherwise reach.
And leave it there. Everything on this page can be assessed without going up, and nothing on it is worth a ladder.
The rest of the series, on the questions people ask most.
Every town has its own page, written around what the roofs there are actually like. Start with the main roof repairs page.
“I needed help removing a chimney.
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We settled that his team would remove the chimney to the roofline, using scaffolding and ladders.
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His team were pleasant and worked efficiently. They got the job done in the estimated time and I was happy with the end result.”
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