If you have a chimney, dormer, or roof valley that keeps letting water in, lead flashing is almost certainly part of the answer - and getting the materials and specification right is what separates a lasting repair from one that fails again in a few years.
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Lead flashing forms the weathertight seal wherever your roof meets a vertical surface - a chimney stack, a parapet wall, a dormer cheek, or the line where two roof slopes meet in a valley. Without a sound flashing, water tracks down behind the tiles or slates at those junctions and works its way into the roof structure. By the time you see a damp patch on a ceiling, the water may have been entering for months.
The lead is cut and dressed - shaped by hand using mallets and dressers - so it sits tightly against the masonry and overlaps the roofing material beneath it. It is then fixed into a mortar joint or a purpose-cut chase in the brickwork and pointed to hold it in place. Done properly, a lead flashing will outlast most other roofing materials by a considerable margin. Poorly fitted lead, or lead that has never been fitted and has instead been bodged with roof sealant and tape, will fail within a few seasons.
This is the angle worth spending time on, because homeowners are increasingly offered alternatives to lead and the marketing around those alternatives is not always balanced. Here is an honest look at the main options available for flashing work in the UK.
Milled lead is the traditional material and, in most situations, still the best. It has been used on British roofs for centuries precisely because it performs well in the real conditions that matter - sustained rain, frost, thermal movement, and wind. Lead expands and contracts with temperature changes, and because it is a soft, malleable metal, it moves without cracking or pulling away from the masonry. A correctly specified and fitted milled lead flashing can last 60 to 100 years.
Lead is specified by code, which refers to its thickness and therefore its weight. Code 3 (1.32 mm thick) is used for soakers - small individual flashings tucked under slates or tiles at abutments. Code 4 (1.80 mm) is the standard for step and cover flashings on chimneys and dormers. Code 5 (2.24 mm) is used in valleys and in exposed locations where heavier gauge is warranted. Using the wrong code is a common cause of premature failure, particularly in valleys where a thin sheet will crack under foot traffic and thermal stress.
The main drawback of lead is cost - both material and labour. Lead is priced by the kilo and the price fluctuates with the metals market. It also takes skill and time to dress properly. There is no shortcut to cutting, bending, and fixing a lead flashing to the standard the material deserves. That cost is, however, a one-off over a very long service life.
Lead theft is a genuine consideration on low-pitched or accessible roofs, particularly on church buildings and outbuildings. On a typical domestic chimney or dormer, the amount of lead involved is small and the accessibility limited, so theft is much less of a concern than it used to be on larger runs of valley or flat-roof lead.
Pre-formed aluminium flashing strips are widely sold in builders' merchants and are sometimes used on domestic roofing work. They are cheaper than lead and lighter to work with. For a straightforward abutment on a simple lean-to roof, aluminium can do an adequate job. The limitations show up in more demanding situations. Aluminium is harder than lead and does not dress as cleanly around complex shapes - chimney corners, curved surfaces, or tight internal angles. It is also more prone to corrosion in coastal conditions and where it contacts cementitious mortar directly without a separating layer, though this matters more in very exposed locations than on a sheltered chimney in March.
Aluminium flashings typically carry a manufacturer's stated life of 20 to 30 years in normal conditions. That is considerably less than correctly specified lead, though it must be set against the lower initial cost.
Zinc is a traditional European flashing material that has become more common in the UK in the past two decades. It is harder than lead but softer than aluminium, and it dresses reasonably well. Zinc develops a natural patina that protects it from further corrosion, and a well-fitted zinc flashing can last 40 to 60 years. It is a reasonable choice for new-build or renovation projects where the architect or designer specifies it, and it can be a sensible option if lead theft is a real concern - zinc has much lower scrap value. It costs more per metre than lead sheet in most cases, and not every roofer is set up to work with it, so check before you commit.
Products like butyl rubber and lead-faced self-adhesive strips are sold as quick repair solutions. They have a place - on a small temporary repair, or as a stopgap while you wait for a full replacement. They are not a permanent answer. Self-adhesive products rely on adhesion to the substrate, and that bond degrades with UV exposure and thermal cycling. Sealant-and-tape repairs to chimney flashings are among the most common reasons homeowners call for a second opinion: the tape has lifted, bubbled, or simply lost its bond and water is getting in again.
If a roofer quotes you for a flashing repair and proposes self-adhesive tape as the primary solution rather than formed metal flashing fixed into the masonry, ask why. There may be a legitimate reason - a very small gap, a temporary measure ahead of a bigger project - but you should understand what you are getting.
A mortar fillet is a triangular bead of cement mortar pressed into the angle between a roof slope and a chimney or wall. It is not a flashing. Mortar fillets crack as the structure moves and as the mortar cures and shrinks. They are a legacy detail from an era before formed metal flashings were standard, and they are still found on older properties throughout this part of Cambridgeshire, including homes near March. If your property has mortar fillets at the chimney, plan to replace them with proper lead flashings at the next opportunity rather than waiting for the fillet to crack and admit water.
Lead work pricing depends on the location on the roof, the quantity of lead needed, the condition of the existing brickwork or masonry, and the access required. The figures below are typical for standard domestic work in this part of Norfolk and Cambridgeshire and are offered as a guide rather than a firm quote - a proper survey of the job is the only way to get an accurate price.
Scaffold or access equipment adds cost where the chimney or dormer is high. Re-pointing of the mortar joints where the lead is fixed is normally included in a flashing job but verify this when you get a quote. If the brickwork itself is damaged or the chimney stack needs repointing beyond the flashing chase, that is additional work.
Knowing what the job involves helps you judge whether the work you are being offered is being done properly. Here is what fitting a chimney flashing should look like.
The old flashing material - whether it is failing lead, mortar fillet, or sealant - is removed. The chase in the mortar joint is raked out to a consistent depth of around 25 mm. The back gutter (the horizontal flashing behind the chimney, which carries water away to the sides) is cut and dressed first, then the step flashings (which follow the angle of the roof slope up the sides of the chimney) are cut and tucked under the tiles or slates individually. The cover flashings are then lapped over the top of the step flashings and wedged or clipped into the raked-out mortar joint. Finally, the joint is pointed with fresh mortar or leadwork pointing compound to secure the lead and prevent water ingress behind it.
The lead should be dressed tightly at every corner. Corners that are folded and dressed properly resist wind uplift and prevent water pooling. Corners that are cut and bodged with sealant are weak points that will open up within a few years. Each section of lead should be fixed with lead clips or lead-headed nails - not left free to move or held in place only by mortar.
Thermal movement is a consideration that good roofers build into the job from the start. Lead expands and contracts significantly with temperature change. On a south-facing roof in summer, a length of lead can reach high temperatures. If a flashing is fixed too rigidly or laid in a single piece that is too long, it will ripple, pull away from the masonry, or crack at fixing points. The Lead Sheet Association recommends maximum lengths of around 1.5 metres for each piece of step or cover flashing. Joining pieces with a proper lapped joint - not a sealant bridge - is the correct way to handle longer runs.
You do not always need to get on the roof to spot a lead flashing problem. These are the signs worth acting on promptly.
A chimney that has not been used for years and has been capped is still a water risk at the flashing level. The lead does not care whether the flue is in use - it still needs to be sound and well pointed to keep water out of the roof structure.
Getting the right job done starts with the right conversation. Here are the questions worth asking any roofer who quotes for lead work on your home.
A roofer who can answer these questions clearly and without hesitation is one who understands the work. A quote that is unusually cheap and vague about materials and method is worth scrutinising before you accept it.
Downham Market Roofers carry out lead work in March and across the surrounding area, including Wisbech, Ely, King's Lynn, and the smaller communities nearby. If you are in March or a neighbouring village and you have a chimney, dormer, or valley that is causing concern, call us to arrange a roof survey so we can assess the flashing and give you a clear picture of what the work involves.
A damp patch does not always point obviously to a flashing failure - it can also indicate missing or cracked tiles, a broken soaker, or a problem with the pointing on the chimney itself. The right repair depends on an accurate diagnosis. Call us to arrange a roof survey and we will tell you exactly what we find and what we recommend, in plain language and with a clear price before any work begins.
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