Upstand first, flashing second
A wall abutment is the line where a roof's surface butts against a wall that stands higher, such as the side of a house beside a rear extension. Rain runs down that wall in every shower, straight onto the junction.
Two parts deal with it. The upstand is the covering itself, turned up the wall so the join sits well above the roof surface and water cannot flow underneath. The flashing is the strip that sits over the top edge of the upstand, tucked into a cut in the brickwork (a chase) or fixed over a trim, so rain running down the wall lands on the flashing, not behind the covering.
Both are needed. An upstand with no flashing is open at the top, and a flashing with no proper upstand has nothing beneath it to protect. The covering must also be fixed to the wall so it cannot slump, because a sagging upstand opens a gap at the top, and that gap is where the leak starts.
Wind-driven rain makes this junction work harder than it looks on a calm day.
Lead, trims and what goes wrong
Flashings are often lead, which bends to the wall and lasts well. MyJobQuote puts lead flashing at over 80 years, which is a lower bound, not a promise. Others use metal trims or a manufactured flashing system fixed over the upstand and sealed along the top.
Lead comes in codes, which are thicknesses. Code 3 suits soakers only; elsewhere, the specification names the code to use, so it should be written down for your job. Sheet lead roofs follow BS 6915, via Approved Document C, not BS 6229. If you are quoted for lead, ask which code goes where and why.
The usual faults are visible from outside or through an upstairs window:
- a flashing that has lifted or slipped out of its chase,
- sealant that has cracked or pulled away along the top edge,
- pointing around the chase that has crumbled,
- an upstand that has split at a corner,
- a gap where the roof and the wall have moved apart.
Sealant alone is a patch. A flashing needs to be properly set and pointed to last.
Where an extension meets the house wall
A rear extension has a roof edge that meets the original house wall, and so it has a long abutment. That line is made of different materials, built at different times, that move at slightly different rates. Over the years a gap can open along that line as the two parts move.
Stains appear on the ceiling next to the wall, or on the wall inside, often after driving rain. Water that gets in at the edge can run along the deck before it shows, so a roofer starts at the abutment.
Our page on replacing a rear extension flat roof covers the wider job. A wall junction can sometimes be repaired alone, with a refixed flashing and new pointing, but if the upstand itself is split or the covering is tired, the new work can last no longer than the covering it joins.
Check that the gutter at the foot of the wall is clear too. A pond at the junction presses against the weakest point, as what happens when a flat roof outlet blocks explains.
Looking at it before pricing
A survey of an abutment looks at the height and condition of the upstand, the flashing and how it is fixed, the pointing and brickwork behind it, and whether the wall is damp inside. The roofer may press the flashing gently to see if it moves, and look along the line for dips where the roof has sagged away from the wall.
Say if the wall is a party wall shared with a neighbour. Cutting a chase into a shared wall can raise party wall questions, and those go to a party wall surveyor, not to building control. Where notice is needed, the Party Wall etc. Act asks for it no less than two months ahead of the start.
Where the junction needs rebuilding, the roofer explains what will be cut out and what will be replaced, so you know the plan before work starts. The total, in writing, comes after the survey. Send photos of the junction from inside and out. Everything we do on these roofs is on the flat roofing page.
