Party Wall Parapets, Upstands and Stack Flashings on Terraces

What an upstand is and why a terrace has them

On many terraces the wall between two houses does not stop at the ceiling joists. It carries on up through the roof void and rises above the slates, and the part that shows above the covering is the parapet or upstand. This is the same wall that carries the shared stack on its crown, so the stack and the parapet are built as one structure rising out of the roof.

The purpose was fire separation as much as weather. A masonry wall that stands proud of the roofs on either side makes it harder for a fire in one house to move to the next along the roof. Builders also found it a convenient way to divide the roof into two clear halves, each with its own falls and gutters. The result is a line of brick that the roof has to finish against along its whole length, with a stack set on top of it at intervals. Where the wall is very tall, a coping or capping of brick, stone or slate usually protects its top edge, and that too has to shed water properly.

That line is the problem. Slate and brick expand and shrink at different rates, and the junction between them is a place where water has to be turned aside every time it rains. If you have read Shared and Party Chimney Stacks: What You Can and Cannot Do Alone you will recognise that the same shared structure causes the same shared problems here.

Cover flashings, soakers and how they meet the stack

Where the roof covering meets the upstand, the junction is weathered by lead. Soakers, the small folded pieces of lead, are interleaved with the slates course by course, and a cover flashing is dressed over their upturned edge and tucked into a chased joint in the brickwork. On a long parapet this becomes a continuous stepped line following the slope of the roof, ending at the stack.

At the stack the flashings change shape. They wrap around the base of the chimney, with an apron at the front, stepped covers at the sides and a back gutter behind it, all connected to the parapet flashings on either side. If one piece is lifted, cracked or has been replaced with a mortar fillet, the whole line is only as good as its weakest length. The difference between lead and cement is set out in Lead Flashing or a Cement Fillet? How to Tell Which You Have.

The flashing is also the part most likely to have been patched. Many parapet junctions carry a history of mastic, felt or cement fillets added over the years, each one hiding the failure of the layer beneath. Lead that has been dressed down properly will outlast all of them, but only if the joint it is tucked into is sound, which brings the pointing of the parapet into the repair. A flashing tucked into a soft or crumbling joint will not stay put, however well it is dressed, so the chase is inspected and re-pointed as part of the job. Where the parapet is also cracking or leaning, that is a repair or rebuild question in its own right.

How trouble shows indoors

The first sign is rarely on the roof. It is more often a damp patch on the party wall at the top of the stairs or in the upper bedroom, a brown stain on the ceiling next to the wall, or a dark line on the loft side of the wall itself. Because the wall is shared, the stain may appear on one side, on both or on the neighbour’s side only, which is where the questions about whose problem it is begin.

Damp on a party wall can come from the parapet and flashings, from the stack above, from a gutter at the roof edge, or from an internal source. The tests that separate them are done from the roof, not by guesswork. Damp on a Chimney Breast: Leak, Condensation or Salts? describes some of the clues, and Is It the Chimney? Working Out Where the Water Is Getting In helps rule out other causes.

Please do not open up the wall or try to trace water from the loft with a ladder at the eaves. Look from the hatch with a torch, note where the staining runs, and photograph it. That information shortens a visit and saves a scaffold if the problem turns out to be a single flashing. It is also worth noting whether the stain changes after heavy rain, because a patch that grows in wet weather and dries in dry weather is far more likely to be an outside water path than a leaking pipe or condensation.

Who looks after what, in general terms

This is general information, not legal advice. In broad terms, each household looks after the roof covering and structure on its own side, and the wall between them is treated as shared in the way party walls usually are. The parapet and the stack on top of it are therefore commonly something both owners have an interest in, and the flashing that serves both roofs is rarely one person’s responsibility alone.

What is actually shared can depend on your title deeds, the way the row was built and what has been done since, so it is worth asking the local council or a surveyor rather than assuming. Work that cuts into or alters a party structure can be notifiable, and the page for chimney repairs in Birkenhead mentions the Party Wall Act. A solicitor or surveyor can tell you where you stand, and a short conversation with your neighbour usually settles more than a letter. If a repair is carried out by one household and benefits both, it is sensible to say so in writing at the time, so that everyone remembers what was agreed.

For the practical side, agree the scope first, ask for a quotation that names the flashings and the parapet pointing separately, and compare what each version includes using What Should Be on a Chimney Repair Quotation?. Our work is on the outside, the parapet, flashings, stack and pots. Anything to do with the flue inside remains with a HETAS or Gas Safe registered installer or a sweep.