If you have damp patches near a chimney, a dormer, or a roof valley, the lead flashing is almost always where the problem starts.
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Lead flashing seals the joints where your roof meets a vertical surface - a chimney stack, a dormer wall, a parapet, or where two roof slopes meet in a valley. These are the points where water will always try to find a way in, and lead is the material that has kept them watertight for centuries. Cut, shaped, and fixed correctly, lead conforms to the masonry, expands and contracts with temperature changes without cracking, and outlasts almost every other flashing material available.
A properly dressed lead flashing is not simply pushed into a mortar joint and left. The lead is cut to the correct width, shaped with a dresser so it follows every irregularity in the masonry, tucked into a chased groove, and fixed with lead wedges before the chase is pointed with mortar. Done right, this is a decades-long repair. Done badly - or bodged with sealant - it will fail within a few years.
Lead flashing does not usually fail all at once. It gives you warning signs first, and recognising them early can save you from a far more expensive repair further down the line. Here are the things to look for, and what each one tells you about the condition of the work underneath.
A damp patch or brown stain on a ceiling directly below or close to a chimney breast is one of the clearest signs that the flashing around the stack has failed. Water travels, so the stain may appear a metre or more from where it is actually getting in. The flashing around a chimney includes the apron (at the front), the back gutter (at the rear), and the stepped or cover flashings on each side. Any one of these can fail independently, and it is worth having each section inspected rather than assuming the problem is limited to where the stain appears.
You may be able to see this from the ground with a pair of binoculars, or from a bedroom window if the roof is a dormer. Lead that has pulled away from the masonry, folded back on itself, or cracked along a joint is no longer doing its job. This often happens because the lead was fixed incorrectly in the first place - either the chase was not cut deep enough, or the lead was not wedged and pointed, meaning it has gradually worked loose. Thermal movement over years of summer heat and winter frost accelerates the process.
The mortar that points over the lead into the chase deteriorates over time - typically faster where a chimney is exposed to prevailing weather. When the pointing crumbles or falls out, rainwater gets behind the lead and tracks down the masonry. From outside, this can look like ordinary repointing work, but if the lead underneath is also corroded or poorly dressed, repointing alone will not solve it. A good repair addresses both the mortar and the state of the lead itself.
White powdery deposits (efflorescence) on the face of a chimney stack, or horizontal tide marks in the brickwork, indicate that water has been soaking into the masonry repeatedly over a long period. This is often caused by a failed back gutter - the lead section that sits between the rear of the chimney and the roof slope above it. Water pooling there has nowhere to go except into the stack. Left untreated, this level of saturation can cause frost damage to the brickwork itself, making the repair significantly more costly.
If the damp appears only during sustained rain and then dries out, it is more likely to be a flashing failure than a tile or slate problem. Cracked tiles tend to let water in more consistently. Flashing failures often allow water in only when rain is driven at a particular angle or when gutters are overwhelmed. Keeping a note of when and where you see damp can help a roofer pinpoint the section of flashing that needs attention.
Mastic sealant, bitumen-based tape, and similar products are sometimes used as a quick fix when a flashing lifts or cracks. These materials shrink and crack within a few years, particularly where they are exposed to UV and frost. If a previous owner had work done with sealant rather than properly fitted lead, the fix will already be failing or close to it. You can often spot this as a dark, gummy residue around the base of a chimney or along a dormer edge.
Understanding why flashing fails is as important as recognising the symptoms. The causes fall into a few clear categories, and knowing which one applies to your roof will help you ask the right questions before any work starts.
Much of the lead flashing on older properties was installed to a lower standard than traditional practice requires. Common faults include lead that was never properly chased in, mortar pointing applied directly over bare lead without wedging, and lead that was dressed cold rather than shaped properly. These problems are baked in from day one and will cause failure earlier than correctly installed lead.
Lead expands and contracts with temperature. This is normal and expected, which is why correct lead work is fixed in relatively short sections with expansion gaps between them. If lead has been laid in one long unbroken run - particularly on a valley or a long dormer - thermal movement will eventually cause it to buckle, crack, or pull free from its fixings. The fix is to re-lay the lead in properly sized sections with the correct clips and overlaps.
Lead does corrode over time, particularly in areas where run-off from certain roofing materials - including some untreated oak or chestnut timber - creates acidic conditions. On most roofs, well-installed lead will last 50 to 80 years or more. Thinner grades of lead used as a cost-cutting measure on older repairs have a much shorter lifespan, sometimes as little as 15 to 20 years. Code 3 lead (1.32mm thick) is the minimum for most flashing applications, with Code 4 or Code 5 used for larger sections and valleys.
The mortar pointing that secures lead into its chase is exposed to the same weathering as any external masonry. On a chimney, this is amplified because the stack is exposed on all sides with no shelter. Pointing typically needs attention every 20 to 30 years, and if it is left until it has fully failed, water entry behind the lead can cause damage that goes beyond a simple repoint.
If a chimney stack has moved, even slightly - through subsidence, thermal cycling of the masonry itself, or deterioration of the haunch mortar at the base of the pot - the chase carrying the lead can crack. Once the masonry cracks, the lead loses its seal regardless of how well it was originally installed. In this situation, a roofer and a builder may both need to be involved to address the cause before the flashing is replaced.
Lead is used in several distinct locations on a domestic roof, and each has its own requirements. Understanding what is where helps you describe the problem accurately and evaluate the quotes you receive.
A thorough repair starts with a close inspection of the affected area - not just the section where water appears to be getting in, but the whole joint or run of flashing. Identifying the full extent of the problem before work starts avoids the need to return for a second repair in the same area shortly afterwards.
Old or failed lead is removed carefully. The chase in the masonry is cleaned out, deepened if necessary, and checked for soundness. New lead is cut to size, dressed to shape, and fitted in correctly sized sections. Lead wedges are driven into the chase to hold the lead in position before the joint is pointed with a suitable mortar or leadmate compound. On valleys, the lead is dressed over timber boards cut to the correct profile, with clips to allow movement at regular intervals.
The materials used matter. Lead sheet for domestic roofing work is graded by code, with Code 3 and Code 4 being the most frequently used for flashings. Code 5 and Code 6 are used for larger areas such as flat valley gutters. Using the correct code for each application is not an optional extra - it determines how long the repair will last.
Lead flashing repairs vary considerably depending on the type of work, the access required, and the amount of lead involved. As a general guide, a straightforward chimney re-flash on a standard house typically costs in the range of £300 to £700 for a mid-sized stack, though a more complex chimney - double stacks, awkward access, or associated masonry repairs - will cost more. Valley replacements are usually priced by the linear metre and can range from around £100 to £200 per metre depending on the complexity and the lead code used. Dormer flashings vary widely based on the size of the dormer and the number of sections involved.
These are typical UK figures across the East Anglia region, including the areas around Swaffham, King's Lynn, and Downham Market. Scaffold access, where required, is usually costed separately. Always ask for a breakdown so you understand what the quote covers - particularly whether it includes making good any associated mortar or masonry.
A few straightforward questions will help you separate a thorough job from a quick fix.
We carry out lead work across Swaffham and the wider area, including neighbouring towns and villages. If you have noticed any of the warning signs described above - damp patches, lifted flashing, crumbling mortar, or previous sealant repairs that are already deteriorating - call us for a roof survey so we can identify what needs doing and give you an honest assessment before any work starts.
Lead work done properly is an investment that should serve you for many decades. Lead work done badly, or patched with sealant, is money spent twice. If you are unsure whether your flashing needs a repair or a full replacement, the only way to know for certain is to have someone on the roof for a close look - and we are happy to do that before asking you to commit to anything.
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