Black Mould: What Every Landlord Needs to Know (and How to Deal with It)

If you’ve ever walked into one of your rental properties and spotted dark patches creeping along the wall or ceiling, chances are you’ve encountered black mould. It’s one of those problems that starts small, almost unnoticeable at first, but can quickly spread and turn into a major headache. Tenants start complaining, walls become damp, and before you know it, you’re looking at not just repair work, but potential legal trouble too.

In this post, we’ll look at what black mould is, how it forms, what your responsibilities are as a landlord under current UK law, and how you can get rid of it properly and put in measures to stop it coming back.

What Exactly Is Black Mould?

Black mould, scientifically known as Stachybotrys chartarum, is a type of fungus that loves damp, humid environments. It usually appears as dark greenish or black patches on walls, ceilings, windowsills, and sometimes even on furniture or behind wallpaper. It’s not just unsightly, it’s a potential health hazard and can have fatal consequences.

When black mould grows, it releases tiny spores into the air that can cause irritation when inhaled. People with asthma, allergies or weaker immune systems are particularly vulnerable, and even healthy adults can develop coughing, wheezing, watery eyes or headaches after prolonged exposure. It’s a problem that needs dealing with quickly, not just to protect the property but also to keep tenants safe and comfortable.

How Black Mould Forms

To understand how to stop black mould, it’s important to know why it appears in the first place. The short answer is moisture. Wherever there’s excess moisture and not enough ventilation, mould can start to grow.

In many UK homes, the main culprit is condensation. This happens when warm, moist air created from something as ordinary as cooking, showering or drying clothes indoors comes into contact with a cold surface like a wall or window. The air cools, turns into water droplets, and before long, that damp surface becomes the perfect breeding ground for mould. You’ll often see it forming around windows, in bathrooms, behind furniture pressed against cold external walls, or near ceilings where warm air rises and cools.

Leaking roofs, cracked guttering or plumbing issues can also lead to what’s known as penetrating damp, which is when water seeps through walls and ceilings. Older properties without a proper damp-proof course can suffer from rising damp, where moisture from the ground travels up through the walls. And sometimes, it’s simply poor ventilation, particularly found in newer homes that are sealed tightly for energy efficiency, trapping moisture inside with nowhere to go.

The Health and Safety Risks

While it’s tempting to view black mould as just another maintenance problem, it’s actually a serious health concern. The spores it releases can aggravate breathing problems and even cause long-term respiratory issues if ignored. For tenants with asthma, young children, or elderly residents, mould exposure can be particularly dangerous.

The tragic case of two-year-old Awaab Ishak in 2020, who died due to prolonged exposure to black mould in his family’s flat, brought this issue to national attention. His story became the driving force behind new legislation designed to ensure landlords never ignore damp or mould complaints again.

Your Legal Responsibilities as a Landlord

Under UK law, landlords have a duty to keep their properties safe, habitable, and free from health hazards. That includes black mould. Several key pieces of legislation make this responsibility crystal clear.

The Landlord and Tenant Act 1985, specifically Section 11, requires landlords to keep the structure and exterior of the property in good repair. That means if mould is being caused by something like a leaky roof, faulty guttering or broken windows, it’s your responsibility to fix it.

Then there’s the Homes (Fitness for Human Habitation) Act 2018, which made it a legal requirement for rental properties to be “fit for human habitation” both at the start of and throughout a tenancy. In simple terms, if mould makes the property unsafe or unhealthy to live in, the landlord must act, even if the tenant hasn’t complained. If you don’t, tenants can take you to court and claim compensation.

More recently, the government has introduced updates under the Renters Reform Bill, which has now passed royal assent and is awaiting full implementation. These changes are designed to ensure that landlords respond promptly to issues like damp and mould, rather than ignoring them or delaying repairs. Under Awaab’s Law, social landlords are legally required to investigate reports of damp or mould within 14 days, begin urgent repairs within another week, and resolve the problem within a reasonable timeframe. Although this currently applies to social housing, it’s already influencing standards in the private rental sector. Local authorities are starting to expect private landlords to follow similar timelines, and its likely future legislation will make that a formal requirement.

Failing to deal with mould can lead to fines, enforcement action, rent repayment orders or even being placed on a rogue landlord register. In other words, this isn’t something to brush aside.

Who’s Responsible, You or the Tenant?

This is a question that comes up a lot, and the answer depends on the cause. If the mould is the result of a structural issue, a leak, poor insulation, or a lack of adequate ventilation, then it’s definitely the landlord’s responsibility. However, if the problem is caused by how the tenant lives in the property, for example, if they never open windows, dry clothes indoors constantly, or refuse to use extractor fans then they may bear some responsibility.

That said, most mould problems are rarely black and white. Even if a tenant’s habits contribute to the issue, it’s still good practice for landlords to educate tenants, provide proper ventilation, and carry out regular inspections. It’s always better to work with tenants to fix the issue than to get caught in a blame game.

How to Get Rid of Black Mould

Once you know where it’s coming from, dealing with black mould properly involves two key steps: cleaning it up safely and fixing the cause of the dampness. Simply wiping the mould away with bleach or a cloth might make it look better for a week or two, but it won’t stop it coming back.

The first thing you need to do is identify the source of the moisture. Check the property carefully for leaks in roofs, gutters, or plumbing. Look for condensation build-up on windows or walls, especially in bathrooms and kitchens. If you’re unsure, a damp meter can help locate hidden moisture, and if the problem seems widespread, a professional damp survey is worth considering.

Once you’ve found the source, deal with it properly. That might mean repairing a leak, improving insulation, upgrading extractor fans, or fitting trickle vents in windows. Sometimes, it can be as simple as servicing an existing fan or providing a dehumidifier to help tenants manage humidity levels.

When it comes to cleaning the mould itself, always take precautions. Wear gloves, a mask and eye protection, as disturbing the spores can release them into the air. Use a specialist fungicidal wash or mould-removal spray rather than household bleach, as these are designed to kill the mould at its roots. Allow the area to dry completely before repainting, and if the mould has penetrated deeply into plaster or wallpaper, you may need to replace the affected materials.

After cleaning, repaint with a mould-resistant or anti-condensation paint to help prevent regrowth. And remember, cleaning is only half the battle. Without addressing the damp or ventilation issue, it will simply return.

Preventing Mould from Coming Back

The best strategy is always prevention. Regular inspections at least once a year and checking in with tenants can help catch early signs of damp before it becomes a bigger problem. Upgrading insulation in older properties can make a big difference too, as cold walls tend to attract condensation. It’s also worth checking that the heating system is working efficiently and that tenants understand how to use it properly; maintaining a consistent background temperature can stop moisture forming on cold surfaces.

Good ventilation is another key part of prevention. Make sure extractor fans in kitchens and bathrooms are working and encourage tenants to use them. You might also consider installing humidity-sensing fans or positive input ventilation (PIV) systems if condensation is a recurring issue. These systems help circulate fresh air through the property and significantly reduce mould risk.

Education plays a role too. Tenants often don’t realise how their daily habits can create condensation. A short, friendly guide explaining how to prevent mould things like keeping windows slightly open, avoiding drying clothes indoors, or running extractor fans after a shower can go a long way in keeping your property healthy.

Why Dealing with Mould Quickly Matters

Black mould is one of those problems that gets worse the longer it’s ignored. It doesn’t just sit there quietly; it spreads. What starts as a small patch in the bathroom can quickly creep across walls and ceilings, damaging plaster, paint and even timber. It can also lead to expensive repairs, loss of rental income, and in the worst cases, legal disputes.

There’s also the human side of it. Living with mould can be miserable for tenants. It smells, it looks awful, and it can make them ill. As a landlord, dealing with it promptly isn’t just a legal duty, it is also a moral duty and a large part of providing a decent, healthy home. Under the new legislation, the expectation is that landlords act fast, take complaints seriously, and keep tenants informed of progress.

Final Thoughts

Black mould is a headache, but it’s not an inevitable one. It can be managed and often prevented with a bit of vigilance and the right approach. If you take anything away from this article, let it be this: mould grows where moisture lingers. Fix the cause, not just the symptom. Keep on top of maintenance, make sure your properties are well-ventilated, and work with tenants to create a healthy living environment.

The recent changes brought about by Awaab’s Law and the Renters Rights Act have made it clearer than ever that ignoring mould is no longer acceptable. Acting promptly not only protects your tenants and your property but also safeguards you from enforcement action or reputational damage. Prevention is always cheaper and easier than cure.

In short, staying proactive about damp and mould isn’t just about compliance. It’s about being a responsible landlord who cares about their properties and the people who live in them. Deal with it early, deal with it properly, and you’ll save yourself a lot of stress and a lot of money in the long run.