If lead flashing around your chimney, valley or roof edge is letting water in, it is worth having it checked before the damage spreads.
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Lead flashing is the metal weathering used to seal the joints where a roof meets a vertical surface - a chimney stack, a parapet wall, a dormer, or where two roof slopes meet in a valley. When it is fitted correctly, using the right code of lead sheet dressed and fixed to British Standard, it can last for many decades. When it is poorly fitted or left to deteriorate, it becomes one of the most persistent causes of roof leaks.
We use code 4 and code 5 lead sheet, which are the grades specified for the vast majority of domestic flashing work. Code 4 (1.8 mm thick) suits most step and cover flashings. Code 5 (2.24 mm) is used where greater durability is needed, such as in wide valleys or on flat roof upstands. Thinner sheet is cheaper to buy but moves more with temperature change and splits sooner.
Lead is dressed - worked with a dresser and bossing mallet - to follow the profile of the roof and stack. It is then fixed with lead tacks or clips and pointed into the masonry using an appropriate mortar. Every stage matters. A flashing that has simply been bedded in mortar without being clipped will pull away within a few years.
Lead work is a skilled trade. It takes time to learn to dress lead cleanly without cracking it, to form a neat internal or external corner, and to understand how much expansion allowance to leave. Not every roofer who offers the service has that skill. Before you agree to any work, the questions below will help you separate those who know what they are doing from those who are guessing.
A contractor who cannot tell you the code of lead they are specifying, or who says only "standard lead", has not thought carefully about the job. The correct code depends on the application. For most chimney step flashings and apron flashings, code 4 is appropriate. For valleys and wider horizontal surfaces, code 5 gives a better result. Ask the question and see whether you get a confident, specific answer.
BS 6915 (Design and construction of fully supported lead sheet roof and wall coverings) sets out how lead should be used, including maximum bay lengths for thermal movement, fixing methods, and lap dimensions. A good lead worker knows this standard by practice even if they do not quote it by number. Ask whether they limit bay lengths to control thermal cracking - in lead work, individual bays should generally be no longer than 1.5 metres. If they look blank, that is a warning sign.
Some roofing firms quote, take the deposit, and then send a labourer or a subcontractor who has never done lead work before. Ask directly whether the person attending your job has worked with lead specifically, not just roofing in general. Skilled lead work should be completed by experienced tradespeople, not general labourers sent to the job on the day.
A contractor who gives you a price without getting on the roof and inspecting the detail has not actually assessed the job. Lead work problems vary considerably - the flashing may have lifted, cracked, corroded, had the mortar fail, or been bodged with sealant at some point. Each of those conditions requires a different approach. Ask the contractor to explain what they have found and why they are recommending what they are recommending.
A common short-cut is to apply roofing mastic or silicone sealant over failing lead rather than replacing it. Sealant over lead is a temporary fix at best and often makes the eventual repair harder and more expensive. It can trap water behind it and accelerate corrosion. If a contractor's solution is to "seal it up", ask why they are not replacing the affected section.
Even a simple quote letter that describes the location, the code of lead being used, and the extent of the work gives you something to refer back to. It also tells you the contractor has taken the job seriously. A verbal quote only protects nobody.
Step flashings on chimney stacks are a frequent source of trouble. These are the individual pieces of lead that interleave with the courses of tiles or slates up either side of a chimney. Over time, the mortar that holds the stepped edge into the masonry raking joints fails. The flashing lifts, wind gets beneath it, and rain drives in behind. This is a repair job in most cases - the existing lead is removed, the raking joints are raked out, and new lead is dressed in and pointed.
Chimney back gutters (the lead tray that sits behind the chimney and diverts water around it) are a less visible but equally important detail. A cracked or undersized back gutter will allow water to pond and eventually find its way through. Replacing a back gutter is a bigger job than replacing step flashings alone - typically a day's work on a standard domestic chimney.
Valley linings in lead can crack along the centre line due to thermal movement if the bays are too long or the lead was too thin when originally fitted. A split valley lining needs full replacement, not patching.
Flat roof lead edges and upstands are another area where poor original installation causes problems. If the upstand height is insufficient or the lead has not been properly welted at the top edge, water tracks back behind it.
Lead work pricing depends on the amount of lead needed, access, and whether any masonry needs making good. As a rough guide, repointing and re-dressing existing chimney step flashings on a typical semi-detached house might fall in the range of £200-£450. Replacing a full set of chimney flashings (step, cover, back gutter and apron) with new code 4 or 5 lead is more involved and commonly costs £500-£900 depending on chimney size and roof pitch. Valley replacements vary more widely with length. These are general UK ranges - your specific job may sit above or below them.
If you have a persistent leak near a chimney, valley or roof edge in Soham, call us to arrange a roof survey. We will get on the roof, inspect the lead detail properly, and tell you what needs doing and why - before you agree to anything.
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Call any time. Calls are answered day and night and passed straight to our roofers.
