Failing lead flashings are one of the most overlooked causes of roof leaks in Burwell - and the warning signs are easy to miss until water is already getting in.
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Lead flashings are the strips of dressed metal that seal the joints between your roof covering and any upstand - a chimney stack, a dormer cheek, a parapet wall, a flat roof abutment. When they work, you never think about them. When they fail, you get a leak that can be running down a ceiling weeks before you trace it back to the roof.
A common problem is that the original lead was installed too thin, using a low Code specification that simply cannot cope with the thermal expansion lead goes through over its lifetime. Lead expands and contracts with temperature changes, and if the sheets are too long, or fixed too rigidly, they split, lift, or pull away from the mortar chase.
Cracked pointing is another early sign to watch for. The lead is usually tucked into a horizontal chase cut into the mortar joint of a chimney or parapet. Over time, that pointing dries out and crumbles, and the lead edge starts to lift. Water then tracks behind the flashing and into the roof structure below.
You do not need to be on the roof to spot the early signals. From ground level, look for:
Inside the property, discolouration on a ceiling near a chimney breast or external wall is often the first sign a homeowner notices. Brown tide marks, fresh damp patches after rain, or paint bubbling on an external wall below a dormer all point to water getting in where lead should be keeping it out.
Poorly installed lead work is one of the most common causes of avoidable water ingress. There are a handful of root causes that come up repeatedly.
Wrong Code lead. Lead sheet is sold in Codes from 3 to 8, with higher Codes being thicker. For most flashings, Code 4 or Code 5 is the correct specification. Using Code 3 saves a small amount of money at installation but the sheet is too thin to last, especially on a chimney that is exposed to wind.
Sheets that are too long. Lead expands and contracts with the seasons. A sheet longer than around 1.5 metres cannot absorb that movement without cracking or lifting at the fixings. Any lead work installed in single runs across a large chimney or long parapet wall needs expansion joints - separate pieces lapped and dressed so they can move independently.
No lead clips or clips missing. The underside of lead flashings on pitches should be held with lead clips every 500mm or so. Without them, wind lifts the flashing edge and water drives in behind.
Sealant used instead of proper dressing. Silicone mastic is sometimes applied as a quick repair to a lifting flashing. It holds for a season at best. The underlying joint is never properly sealed, and the mastic itself degrades with UV exposure.
A standard chimney stack needs several separate lead components to be watertight. The front apron sits at the lowest point where the chimney meets the roof slope. Step flashings weave up the sides of the stack between each course of tiles or slates. A back gutter sits behind the stack to collect any water that runs off the back face. Cover flashings, tucked into the mortar joints, overlap all of these to shed water away.
Each piece needs to be cut and dressed individually on site. This is not work that can be done to any useful standard with preformed strips from a builders' merchant. The pieces need to fit the actual geometry of the chimney and the actual pitch of the roof. On older properties, chimney stacks are rarely perfectly square, and a good tradesperson allows for that when they measure and cut.
Dormer windows are a particularly common source of lead failures because there are multiple junctions to seal - the sides, the base, and often the top where the dormer cheek meets the main roof slope. The lead on dormer cheeks also tends to be large in area, so correct Code selection and correct detailing of expansion joints matters even more.
Where a flat roof abuts a vertical wall - a common detail on extensions - a lead flashing is dressed up the wall and into a chase in the masonry. The flat roof itself needs to be correctly prepared with an upstand for the lead to lap over, and the lead needs to be high enough to stay above any water that ponds on the flat surface. A minimum upstand of 150mm is generally considered good practice.
Not every failing flashing needs a full replacement. If the lead itself is in good condition but the pointing has failed, re-pointing the chase and re-securing the lead edge is sometimes all that is needed. If the lead has cracked through, split at expansion joints, or is thin Code 3 material that has reached the end of its life, replacement is the only sensible course.
A patch repair with sealant is not a proper solution - it delays a proper repair and usually means more work later when the underlying damage is found to have spread.
Good quality lead work, done to the correct Code specification with proper expansion joints and clips, can last several decades. Thin or poorly dressed lead, or lead that has been bodged with sealant repairs, can fail within a few years of installation.
Lead is used on all roof types. On tiled roofs and slate roofs alike, the principle is the same - a dressed metal seal at every junction where the waterproofing layer cannot run continuously. On flat roofs, lead is used at the wall abutments and sometimes at upstands around roof lights or drainage outlets. The Code used may differ depending on the application, but the standard of workmanship required is equally high in every case.
We carry out lead work repairs and replacement across Burwell and the surrounding area, including nearby towns and villages. We cut and dress lead on site to the correct Code for the application - no preformed strips, no sealant bodges.
If you have a stain on a ceiling near a chimney breast, a dormer that has started to let in water, or you can see from the ground that the lead on your chimney has lifted or cracked, call us to arrange a roof survey. We will tell you what the problem is and what it will take to fix it properly.
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Call any time. Calls are answered day and night and passed straight to our roofers.
