How to Deal with Damp and Mould in a London Rental Property

Few maintenance issues worry London landlords quite like damp and mould. They look alarming, they can spread quickly, and they sit at the meeting point of the building's condition, the weather and the way a home is lived in. The good news is that most cases are manageable once you understand the cause and act promptly. This guide walks through the common types of damp, who is responsible for what, and the calm, methodical steps that resolve the problem and protect your property and your tenants.

Why damp and mould are so common in London homes

Much of London's rental stock is made up of older, solid-walled period conversions and flats that were never designed for the way we live today. Modern life produces a surprising amount of moisture: cooking, showering, drying laundry indoors and simply breathing all add water to the air. When that moisture meets a cold surface and cannot escape, it condenses, and persistent condensation is the most frequent cause of the black spotting most people recognise as mould.

That does not mean it is automatically anyone's fault. Damp is usually a combination of factors, which is exactly why a calm, evidence-led approach works better than apportioning blame at the first sign of a problem.

Know your three types of damp

Getting the diagnosis right matters, because the remedy is completely different in each case. Broadly, there are three things you may be dealing with.

• Condensation: moisture in warm indoor air settling on cold surfaces such as windows, external walls and behind furniture. By far the most common.
• Penetrating damp: water getting in from outside through a defect, such as a cracked render, a slipped roof tile, a failed gutter or blocked downpipe.
• Rising damp: ground moisture travelling up through walls where a damp-proof course is missing, bridged or has failed.

If a patch only appears in cold weather, sits in corners or behind wardrobes, and wipes off, it is most likely condensation. A stain that worsens after rain, or a tide mark low on a wall, points to a building defect that needs investigation rather than ventilation advice.

Where responsibility sits

As a landlord, you are responsible for keeping the structure and exterior of the property in repair and for ensuring the home is fit to live in. A genuine building defect, a leaking roof, failing pointing, an inadequate or broken extractor fan, falls squarely within your repairing duties, and these obligations sit alongside your wider landlord repair and maintenance obligations. They cannot be passed to the tenant.

Tenants, in turn, are expected to use the home in a reasonable, tenant-like manner: ventilating where they can, wiping down condensation, and most importantly reporting problems early rather than letting them develop unseen. The key point is that you should never treat condensation as simply the tenant's lifestyle problem. The right response is to investigate the building first and work collaboratively from there.

The new duties you should be aware of

The rules around housing conditions are tightening, and damp and mould are squarely in scope. Under the wider reforms arriving with the Renters' Rights Act 2025, the Decent Homes Standard and Awaab's Law-style hazard timescales are being extended to the private rented sector. In practice this means landlords are expected to investigate and address serious hazards such as damp and mould within set timeframes once they are reported.

The direction of travel is clear: ignoring a report, or telling a tenant to simply open a window, is no longer a safe response. Acting quickly and keeping a record of what you found and did is now both good practice and increasingly a legal expectation. This is general information rather than legal advice, and you should consult a professional on your specific obligations.

A calm, step-by-step response

When a tenant reports damp or mould, a consistent process gives you the best outcome. Start by acknowledging the report quickly and arranging to inspect, ideally in person. Look for the pattern: where is it, when did it appear, is there a visible leak or external defect?

If you find a building issue, instruct a tradesperson to fix the underlying cause, not just the symptom. If it looks like condensation, check that extractor fans in the kitchen and bathroom actually work and vent outside, that trickle vents are present, and that there is no obvious cold bridging. Having a clear system for logging and tracking these issues, as we cover in our guide on handling maintenance requests in London, means nothing slips through the cracks and you have a record if a dispute ever arises.

Treating the mould and preventing its return

Visible mould should be cleaned safely using an appropriate fungicidal treatment rather than simply painted over, as paint alone traps the problem and lets it return. But cleaning is only ever half the job: unless the underlying cause is addressed, the mould will come back within weeks.

Lasting prevention usually comes from a combination of measures: working extraction in wet rooms, adequate background ventilation, and, where the building allows, attention to insulation and heating so surfaces stay warmer. Small, practical changes often make a real difference, and they reassure tenants that the problem is being taken seriously rather than blamed on them.

Protect yourself with good records

Damp can occasionally surface at the end of a tenancy, when a check-out reveals mould that was not there at the start. This is where a thorough check-in inventory earns its keep, giving you a dated, photographic baseline of the property's condition. Any deduction from a deposit must reflect genuine damage beyond fair wear and tear, and condensation arising from a building issue would not usually qualify, so clear documentation protects everyone and keeps disputes rare.

Good records also help you spot a recurring pattern in a particular property, which may point to a structural cause worth resolving once and for all rather than treating season after season.

Where a managing agent helps

Damp and mould reward early, organised action, and that is hard to deliver if you are managing remotely or juggling several properties. A good managing agent will respond to reports quickly, arrange the right inspection, instruct trusted tradespeople and keep the paper trail in order, which is a large part of what a letting agent does day to day.

If you would like a calm, methodical pair of hands looking after the condition of your London property, JSLA works with many landlords across west London and would be glad to talk through how we approach maintenance and tenant care. There is no pressure, just useful guidance whenever you need it.