What is a lead roll?

What you are looking at on a lead roof

Look at a lead flat roof, a bay roof or a porch from an upstairs window and you will see a pattern of raised lines. Those running down the slope are rolls. Those running across it, in steps, are drips. Together they divide the roof into bays of manageable size, each covered by a single sheet of lead.

The roll is a joint. Two edges of lead meet over a rounded timber strip, known as the core, nailed down to the deck. The first sheet is worked up and across the core. The second is worked over the top and wraps the first. What you get is a smooth, round seam, a little like a cord laid on the roof, with the lead folded round it.

The shape does the work. Because the join stands proud of the deck and the lead wraps over it twice, rain running down the roof cannot find a path across. Water is carried past on both sides of the roll and continues to the gutter. A good roll is neat, even and tight to the core.

Why rolls are used instead of soldered joints

Lead is among the most workable roofing metals, and in principle two sheets could be joined by soldering or welding along a flat seam. On a roof that approach asks for trouble, because lead moves. It grows when warm and shrinks when cold, and a rigid joint has nowhere to go, so the stress builds up until something gives.

A roll deals with that in a mechanical way. Nothing glues or solders the sheets together at the seam. Each is held at its outer edge by clips and is free to slide a little under the wrap of its neighbour. As temperature changes, the sheet moves within the roll without tearing, and the joint stays closed.

That is why the traditional form is so durable. A lead roof laid with correct rolls and drips can last a very long time. One cost guide reports lead flat roofs lasting 50 to 100 years where properly laid, and a lead flashing guide puts a flashing at over 80 years. These are typical figures and depend on workmanship, exposure and upkeep, not a promise. Our page on drips in lead gutters explains the matching detail across the fall.

Types of roll you may meet

The usual form on a flat or bay roof is the wood-cored roll, sometimes called a batten roll. A tapered or rounded timber core is fixed to the deck, and the lead is dressed over it as above. It is the form most roofers mean when they say roll.

A hollow roll is a variation in which the lead is formed into a rounded seam without a timber core, relying on the folds themselves to give the shape. It is used in some details and by some traditions, but it is less common on a modern lead roof, and it needs a skilled hand.

Standing seams and similar joints are used on other metals such as zinc and copper, where a different jointing system applies. On lead, the roll is what you will usually find.

Which type was used originally may matter to a listed building. If a roof has rolls of a particular form, copying them is part of putting the roof right, and a conservation officer may ask to see the detail. Our page about box gutters shows how rolls and drips combine in a larger run.

How rolls go wrong

Rolls are hardy but not immune to faults, and the age of the lead, the weather it has faced and the quality of the original laying all play a part. The main problems we see are listed below.

• Cracks along the crown. The lead is stretched where it wraps the core. Thin sheet or too much tension can split it.
• Rotten cores. A timber core that has taken in water will rot and shrink, leaving the lead loose and misshapen.
• Lifted or crushed seams. Foot traffic and fallen branches flatten a roll, closing the channel that keeps the sheets apart.
• Poor workmanship. A roll that is under-lapped or not clipped will fail in the first hard winter.
• Theft damage. Where sheets have been stripped, the cores and clips are often left bent or broken.

Diagnosis needs the roof to be examined closely, and often the lead is lifted at the edge to see the core. A roll that looks sound from above can hide a wet core.

Rolls and the regulations

Relaying a lead roof, including the rolls and the deck beneath, can bring Building Regulations questions, mainly about insulation, as described on our page about Building Regulations for lead roofs. The roll itself is a detail of the covering and not a regulated item.

On a survey we examine the rolls, record their condition with photographs and say whether they can be kept, repaired or reformed. Repair of a short length is often possible, and a full relay is considered only when the sheet and the deck are both beyond saving. A useful check from the ground is whether any roll looks flattened or split along its top, since foot traffic and ladders often crush a roll long before the weather wears it out.

If you have a lead roof with raised seams and want to know their condition, ask about our lead roofing service, which covers Bath and the towns around it.