What are rolls and drips on a lead roof?

Lead expands when it warms and shrinks when it cools. A single big sheet would drag against its fixings every day and eventually split, usually along a fold or beside a fixing. So a lead roof is cut into panels, each fixed along its top edge and left free to slide at the sides and bottom.

That arrangement needs a way of joining one panel to the next that keeps the water out while still letting the metal move. Rolls do this for the joints that run down the slope, and drips do it for the joints across it. If you can see raised ribs and small steps on a lead-covered surface, the roof has been laid the traditional way. If you see none on a large lead roof, ask why, because the metal has to go somewhere when the weather changes, and a roof with no allowance for movement will find its own.

A roll is a length of timber, rounded on top, fixed to the deck along the line where two panels meet. One sheet is wrapped up and across the timber, and the neighbouring sheet is turned over it, so the seam sits above the line where water runs and the lead can slide a little either way. On the finished roof it reads as a neat, raised rib.

There are two types. A solid, or wood-cored, roll has the timber inside the lead, with the sheets lapped over it. A hollow roll is formed from the lead itself and is generally kept for smaller work. The spacing is set by the width of sheet being used and the thickness of the lead. Published leadwork guidance gives the maximum sizes for each, and we can show you which figures apply to your roof when we survey it. Narrower panels and closer rolls are usual where the lead is thinner.

A drip is a step in the deck, built by the carpenter, with the upper sheet turned down over the edge and the lower one tucked beneath. It breaks the roof into lengths along the fall of the surface, so each length is short enough to stay in place and can move without tearing.

Drips also form the fall of a flat lead roof or gutter in steps. Water leaves each sheet cleanly at the lip, never sits in a hollow and cannot be driven back up the joint by the wind. A lead gutter laid without them would need one unbroken run, and a long run is where cracking begins. Our answer on box gutters and parapet gutters shows drips in use, and explains how the steps are spaced along a hidden channel. Where a roof has a long fall, there may be several drips in a row, each one a short stage on the way down.

Rolls and drips are built into the deck before the lead goes down, and the deck must be sound, dry and set at a fall for water to leave. If the boards are rotten, the lead will follow them down. If the falls are wrong, the rolls and drips will make a tidy pattern over a roof that holds water.

This is why a lead job often starts with carpentry. The decking is checked, repaired or relaid, and the rolls and drip steps are formed on top. Our guide to a lead flat roof covers how the whole build-up goes together. For the thickness of the lead itself, see our lead codes guide, where Royston lists codes 5 to 8 for gutters and flat areas. The carpenter and the leadworker need to agree the layout first. Changes to the plan once the lead is cut are costly, so it is better to settle them on the deck.

Ask where the rolls and drips will go, which direction they run, and what the lead code is. A written quote should describe a roof that can drain, with a deck laid to a fall and the sheets divided into manageable panels. If a quote describes a single wide sheet of lead with no joins, it is worth asking how movement is handled and who will answer for a split in a year.

Cost follows how many rolls and drips the layout needs, which in turn follows the area, the outline, how much deck needs repair and the access. After our survey you receive one total price, set out in writing. Our lead roofing and leadwork page covers the rest of our lead work, and a set of survey photographs shows the condition of the existing rolls and joints. We describe the layout in the quote.