When a Balcony Leaks Into the Flat Below

The short answer: a balcony is a small flat roof over somebody's living room, so the person underneath discovers the fault first and the person above it hears about it second. The water almost never enters where the stain appears, and in a block the question of who is responsible usually has to be settled before anyone can agree what to repair.

Why does the flat below find out first?

Because the balcony is doing two jobs and only one of them is visible. Above, it is a floor: tiles, decking or a screed that somebody walks on, puts furniture on and sweeps. Below, it is the ceiling of a home, and the waterproofing that separates the two is buried between them where nobody sees it.

So the failure is silent upstairs and obvious downstairs. By the time a mark spreads across a neighbour's ceiling, water has usually been getting past the waterproofing for a while, running across a structural slab and finding a way down at whatever point it reached first. The resident above sees a balcony that looks exactly as it did last year.

Where does the water actually get in?

Three places account for most of it, and only one of them is the bit people picture.

• The threshold. The single commonest entry point. Where the door sill meets the balcony there has to be enough drop for water to run away rather than back inside, and enough waterproofing carried up behind the frame. Add a new floor finish over the old one and that drop shrinks; add two and it disappears.
• The drainage. A balcony drains through one or two small outlets, and small outlets block. Behind a blocked outlet the water rises above the level the waterproofing was designed to hold, then goes wherever it can, which is usually inward at an upstand.
• The wear layer and what sits on it. Tiles lifting, grout gone, a balustrade post bolted straight through the waterproofing, a planter that has sat in the same spot for a decade. Every fixing through a waterproof layer is a hole that was sealed once and has been weathering ever since.

Water pooling where it should not is a warning sign on a balcony for the same reasons it is on any flat surface, covered in the piece on standing water.

Why does responsibility come before the repair?

Because in a block the balcony is often not straightforwardly anyone's to fix. Depending on how the lease is written, the structure and the waterproofing may be the freeholder's responsibility while the surface finish belongs to the leaseholder, or the whole thing may be demised. The answer is in the lease and it varies building to building, which is why nobody should take a general statement from a website as applying to theirs.

What settles it in practice is knowing where the water enters. A failure at the structural waterproofing is a different conversation from a cracked tile, and both are different again from water arriving from the balcony above. That is a matter of fact, established by looking, and it is the reason a survey tends to be the first thing commissioned rather than the last. Managing agents deal with this pattern constantly, which is why it appears on the property and block management page alongside the reporting that makes it forwardable.

What does the inspection settle?

Where the water is entering, what has failed, whether the surface has to come up, and what the repair actually is. It looks at the threshold and the drop behind the door, the outlets and whether they run, the upstands where the balcony meets the walls, every fixing through the deck, and the condition of whatever is walked on. Where the balcony above is a candidate, that gets checked too, because eliminating it is as useful as finding it, and on a stack of identical balconies the same fault is often present on several at once.

One thing it cannot do is tell you how long the water has been getting in, and that matters more than it sounds. Damage to a ceiling below accumulates quietly, so by the time it is reported the plaster may need replacing rather than drying. Establishing the entry point early is the only thing that limits that, which is why a complaint from downstairs deserves an inspection rather than a season of watching to see whether it happens again.

The output is a written answer with photographs, which is what a leaseholder, a freeholder and an insurer can each be shown without anybody having to take a neighbour's word for it. What follows is balcony waterproofing designed around what was found: the threshold rebuilt where it has no drop left, the outlets put right, and a continuous layer taken up every upstand rather than patched at the spot the stain suggested.