Question answered
What are rolls and drips on a lead roof?
The short answer
A roll is a raised seam that follows the slope of a lead roof, where two sheets meet over a shaped timber batten. A drip is a step across the roof, where one level drops to the next. Together they divide the roof into bays so each sheet can expand and contract freely without splitting, and they let water run away.
Rolls and drips are the joints that divide a lead roof into sections. They look like small details, but they are what stop the metal tearing itself apart as the weather changes.
Why lead needs joints at all
Lead swells in the warmth and contracts in the cold, and it does so every day. A single large sheet fixed tightly in place has to take all that movement in one piece, and over the years it tires and cracks. The remedy is to lay the roof in smaller bays and let each slide on its underlay.
Rolls and drips are how the bays are joined. They hold the sheets together and keep rain out, while still allowing the lead to move. A roof that has them in the right places can last for generations. A roof without them, or with them badly made, cracks along the line of least resistance.
This is why a lead roof is never one smooth sheet. The pattern of lines across an older lead roof is the pattern of its movement joints, and each has a job to do. Our hub on lead roofing gathers the other topics.
Rolls: the raised joints
A roll runs up and down the slope. A rounded wooden batten is fixed to the deck, and the lead from each side is turned over it. In a wood-cored roll, one sheet is dressed over the core and the other is lapped across it and dressed down, leaving a rounded bead that sheds water and gives the lead room to move.
There are two main kinds: the solid-core roll, with a timber batten inside, and the hollow roll, a more traditional shape in which the lead is formed round on itself. Both are used on British roofs, and the choice depends on the building and the lead code.
Rolls are spaced so that each bay is a size the lead can cope with. Leadworx recommends code 5 for general work and code 6 for large roofs, since thicker lead copes better with bigger bays. A roll crushed by boots, or one that has opened at the top, is a typical source of leaks.
Drips: the steps across the fall
A drip is a step built into the deck, often about a hand high, running across the roof. The lead at the top of the step is dressed down over its edge, and the lower sheet is tucked underneath. Water runs off the upper level, drops over the step and carries on down the next bay.
Drips do two jobs. They cut long runs of lead into workable lengths, and they give the roof its fall, because the deck steps down in stages and not in one continuous slope. With no step, wind can push water back up under a joint.
IKO's flat-roof guidance, citing the 2018 edition of BS 6229 (since revised), gives 1:80 as the finished minimum fall and 1:40 as the design fall. Drips are one of the ways a lead roof gets that fall without a very thick deck. A drip set too low leaks in a gale. Gutters use the same device, and how long a well-jointed roof can be expected to last is on lead roof lifespan.
What goes wrong with them
Common faults include rolls crushed by foot traffic, lead split along the edge of a drip, a roll never properly fixed down at its ends, and old lead that has fatigued where it bends. Movement joints sealed with mastic, or painted over, can lock the lead and cause cracks.
The signs inside are water marks or damp on the ceiling under the roof, usually after rain. Outside, a split or an open roll end is often visible from a ladder at the edge. The lead should look flat and clean, and a bay that has bulged or buckled has been under strain, often because a fixing has pinned it where it ought to slide.
Repair of these joints is covered on repairing a lead flat roof. A smear of sealant on a split is a short-term measure, nothing more, and the underlying movement carries on beneath it.
Why the joints still matter in modern work
Lead stays in use because it is long lasting and can be dressed to any detail. A lead flat roof is put at 50 to 100 years by Less, a range that depends on good joints. Why roofers still use lead explains the appeal, and lead alternatives compares other materials.
Single-sheet rubber and fibreglass systems are laid in larger pieces with fewer joints, but they have their own details at edges and upstands. Each material has movement to manage. With lead, the roll and the drip are the answer.
When we survey a lead roof, these joints get a close look early on, because they show whether the roof has been moving freely. You see photographs of them, and the quote that follows is written as one price. Where a roll has opened or a drip is too low, it is shown to you before anything is priced.
Rolls and drips: two more questions
Can I walk on a lead roof with rolls?
Take care. Rolls can be crushed under boots, and thin lead dents and tears. If you must go on it, keep to the flat bays between the rolls and wear soft shoes. Better still, use a ladder and a camera, or ask a roofer.
How many rolls does a lead roof need?
That depends on the lead code, the width of the roof and the fall. The lead needs bays small enough to move freely, so a roofer sets the spacing from the sheet thickness and the deck. The survey confirms it for your roof.
Tell us about your roof
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