Plumbers & electricians in Rotherhithe

The Surrey Commercial Docks filled this peninsula until the early eighties, and when they closed over ninety per cent of the dock water was infilled and built over. Greenland Dock, South Dock, Surrey Water and the lake at Canada Water are what survived. The rest was replaced in waves: late eighties and early nineties housing around Surrey Quays, a long run of apartment blocks after it, and the taller, denser work around Canada Water now. Older Bermondsey streets and a few warehouse conversions sit around the edges.

That history matters more than it sounds. A house built in 1900 leaks air through a hundred small gaps and ventilates itself whether anyone wants it to or not. A flat built to a modern airtightness standard does not. It has been deliberately sealed, and every bit of moisture made inside it, from showers and cooking and drying washing and simply breathing, has to be carried out by machinery.

So the work here splits differently to older parts of south east London. Less lead pipe and cracked clayware, though a blocked drain in Rotherhithe’s older terraces still turns up often enough, and far more sealed systems and calls that begin with black mould in a corner and end at a fan that has not run properly in years.

Why a Rotherhithe flat gets mould when nothing is leaking

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Airtightness is the point of a modern flat, not a fault. Tight windows, sealed junctions and insulated walls hold the heat in. The trade off is that the building cannot breathe on its own, so ventilation is designed in as a machine. In most flats around Canada Water and Surrey Quays that means either continuous mechanical extract, a small fan running quietly all day at a low rate and boosting when the bathroom is used, or full MVHR, which draws stale wet air out of the kitchen and bathroom and feeds tempered fresh air back into the bedrooms through ducts. Both are meant to run permanently. A household of four puts several litres of water into the air every day, and if the machine stops, that water stays.

From inside it rarely looks dramatic. Black speckling in the top corner of a bedroom, usually an outside corner or the wall behind a wardrobe. Windows running with water on cold mornings. A bathroom still wet hours after a shower. Coats in a built in cupboard smelling musty. People reasonably assume something is getting in from outside, and in a flat several floors up with dry neighbours below, it almost never is. Moisture made indoors had nowhere to go and condensed on the coldest surface it could find, which is why it appears in corners and behind furniture rather than in the middle of a warm wall.

The fix starts with proving the extract actually moves air, because a fan can hum convincingly and shift almost nothing. Measuring the flow at the terminal is the only honest way to know. After that it is usually something ordinary. Filters left in for years and clogged solid. A flexible duct crushed or kinked in a ceiling void. An external grille packed with dust or a bird nest. A boost switch or isolator turned off by someone who took the constant hum for a fault. Or a system commissioned to the wrong rates and never balanced. The one thing worth saying plainly is that taping over trickle vents or blocking a wall grille makes it worse every time. It feels right because the draught stops, but the extract still pulls air out and now it has no clean path back in, so the flow collapses and the moisture stays. Wiping mould off the paint deals with the stain. The cause is air that is not moving.