The short answer
A drip is a vertical step built into a lead gutter or flat roof deck, where the upper sheet of lead overlaps the lower one and water falls over the edge. Drips let the lead be laid in short lengths that can move with temperature, and they carry water down the fall of the roof. Without them, long sheets would stretch, crack and let water in.
The step that makes a flat gutter work
Picture a lead gutter running along the back of a parapet. It is not a smooth channel from end to end. Along its length the bed drops in a series of small steps, a bit like a staircase laid on its side with very shallow treads. Each step is a drip. The lead above it runs on to the edge of the step, turns down the vertical face, and sits over the sheet that begins at the foot.
The point of the step is that water cannot creep backwards. A plain overlap on a nearly level surface would let rain be drawn sideways by capillary action, the pull that moistens a gap between two close surfaces. A vertical drop breaks that pull, so the water falls clear. The joint stays dry because gravity, not sealant, does the work.
The same device appears on lead flat roofs and on the beds of box and parapet gutters, the hidden channels that carry rain from large areas of roof. Our guides to parapet gutters and to lead rolls show how the two details work together across a whole deck.
Why gutters need falls and steps
Any flat roof or gutter has to drain. For flat roofs, BS 6229 guidance quoted by manufacturers calls for a finished fall of no less than 1 in 80, with the design set at 1 in 40 to absorb building tolerances and sag, so the surface never ends up level. A gutter bed has to follow that rule, and a long run falling at that rate would sink a long way over its length.
Drips solve that. Instead of one steady slope, the bed is made of short flat or gently falling lengths separated by steps, and the steps give the total drop the gutter needs. The amount of fall in each length is small, and the step does the rest of the work of taking water down to the outlet.
The second reason is movement. Lead warms and cools with the day and the seasons, growing and shrinking as it does so. An over-long sheet is pinned in place at both ends, so it is dragged out on a hot day and then tears on a frosty night. Cutting the run into lengths at drips lets each sheet move within its own limits. Heavier lead codes allow longer lengths between drips than lighter ones, and the manufacturers' tables set the limits for each.
How a drip is built
On the roof deck, a drip is formed in the timber first. The boards at the step are cut so that the upper deck sits higher than the lower one, with a vertical face between them. The face is finished with a batten or a shaped timber, and the whole deck is covered with an underlay, which is a soft layer laid under the lead to protect it from rough boards and nail heads and to let it move.
The lower sheet of lead is laid first. It is dressed up the face of the step and tucked beneath the upper sheet. The upper sheet is then laid over, turned down the face and left clear of the lower lead. It is not nailed through the visible surface, since a nail hole in a gutter is a future leak. Clips and fixings are placed where the lead is covered, so the exposed metal is not pierced.
Dressing the lead takes skill. A sharp fold stresses the metal, and a badly formed drip can crack where it bends. The standard is a rounded, even fold, with enough overlap that wind-blown rain cannot reach the joint. It is one of the details that distinguishes tidy leadwork on a roof from a rushed job.
How drips fail
Drips are small details that carry a heavy load, and the same few faults appear again and again.
- Cracks across the fold. Repeated movement and old, brittle lead can split at the bend. Splits are easiest to spot once the gutter has been emptied, as clearing parapet gutters explains.
- Debris lodged at the step. Leaf litter packs against the upstand and holds water, so the lead is wet for long periods and the step overflows.
- A step that is too low. Where the drop is shallow, wind and heavy rain can drive water back over the edge.
- Poor laps. If the overlap is short, or the sheets are not tucked, water finds the gap.
- Sagging boards. A rotted deck changes the fall, and the water ponds above the drip instead of crossing it.
Most of these can be seen once a gutter is cleared and the lead is dry. A torch is useful, and so is patience, since a hairline crack is easy to miss.
Repairing or reforming a drip
A small split in a drip can sometimes be repaired by cutting out the damaged lead and welding or patching a new piece, as long as the surrounding sheet is sound. If the fold is cracked at several points, or the boarding beneath has sagged, the sensible repair is to reform the drip, with the deck corrected and new lead laid to the right code and length.
Choosing the right code matters because a thin sheet will not stand the movement that a heavier one takes in its stride. Code 5 and code 7 are both used for gutters, and the correct choice depends on the length of each section and where it sits. A survey establishes this before the work starts.
Sealant on a drip is only a temporary measure and often makes things worse, because it traps water. Typical UK prices for leadwork are covered in our guide to leadwork costs, and the main lead roofing page explains how we carry out repairs, with your fixed quote arriving after the survey visit.
