What are the most common causes of mould?

Damp and mould in a home can really affect a person’s health and decrease the value of a property, so needless to say, it’s not something a landlord should take lightly. Plus, it’s legally a landlord’s obligation to keep this side of their property in working order. Caused by excess moisture, removing mould is usually a costly job carried out by professionals, so it’s important to take precautions and avoid it where possible.

For landlords, understanding the causes of mould is important because the right response will depend on where the moisture is coming from. Sometimes mould is linked to everyday condensation from cooking, showering, or drying clothes indoors. In other cases, it may be caused by defects in the property, such as leaks, poor insulation, blocked guttering, or inadequate ventilation.

Leaking pipes, faulty roofs, window frames, and a lack of ventilation can all be the culprits of mould growth. It needs to be caught and dealt with early, which can be an issue if you’re not the one residing in the property day-to-day. So how can you make your rental property as mould-resistant as possible?

Here, we’ll go through what mould is, what the main causes of mould in rented homes are, when landlords may be responsible, and what you should do if a tenant reports damp or mould in your property.

What actually is mould?

Mould is a fungus that generally grows in damp and poorly ventilated areas. For mould to grow, it needs a food source such as wood, drywall, or cotton; darkness, warmth, oxygen, and moisture. The problem is, most of these conditions are inevitably present within homes, and the only one that can really be controlled is moisture.

This is why moisture control is so important. Without moisture, mould is far less likely to develop. But once damp conditions are present, mould can spread quickly and become much harder to deal with.

A property with mould is likely to put prospective tenants off instantly. It’s the sign of an unhealthy house, possibly with a bad structure, and most of all, it’s bad for our health. It’s particularly bad for babies and children, the elderly, those with an already weakened immune system, and those with respiratory issues and allergies. Mould can not only worsen respiratory problems, but it can also cause them and trigger asthma attacks. It also produces allergens, irritants, and, in worst cases, toxic substances. All in all, it’s not something you want to welcome into your property.

GOV.UK guidance also makes it clear that damp and mould can affect the airways and lungs, as well as the eyes, skin, and mental wellbeing. This is why landlords should treat reports of damp and mould seriously, especially where children, older tenants, pregnant women, people with asthma, or tenants with weakened immune systems may be affected. (Gov.UK)

You can read more about wider safety duties in our guide to a landlord’s responsibility for tenant safety.

The most common causes of mould

There are a number of different things that can lead to mould. So, what are the main causes of mould in a rental property? In most cases, mould is linked to excess moisture. The difficult part is working out why that moisture is there.

Condensation is essentially excess moisture, so it can often be the cause. Condensation can collect on pipes, concrete floors, and on walls, making these places prime hot spots for mould growth. Poor ventilation can also contribute, as it creates pockets of stagnant moist air.

Condensation usually happens when warm, moist air meets a cold surface, such as a window, wall, or ceiling. Everyday activities like cooking, showering, boiling a kettle, drying washing indoors, and even breathing can all add moisture to the air. If the property is cold, poorly insulated, or not properly ventilated, that moisture is more likely to settle and lead to mould.

Leaks are, of course, the most obvious cause of mould; however, they’re not always so obvious. The worst leaks are the ones that are hidden, such as inside walls. They’re usually discoverable by the mould that’s begun to visibly grow, and by this point, the damage is done. The same can happen in roofs, so make sure you or your tenant checks the attic regularly for leaks.

Mould can also be caused by penetrating damp, which happens when water enters the property from outside. This could be due to damaged roofing, broken guttering, cracked brickwork, faulty pointing or leaking window frames. Rising damp can also be an issue, especially in older homes, where moisture from the ground travels up through the walls.

It’s also inevitable that mould growth will occur if you’re unfortunate enough to experience any flooding. It only needs a suitable surface to be wet for 24 hours before it will do its thing, so flooding poses a pretty big risk. Not only this, but flooding creates the perfect, more extreme environment for some dangerous and toxic moulds that can cause bigger problems.

Condensation or a property defect?

One of the most important things landlords need to do is work out whether mould is mainly caused by condensation from everyday living or whether there is an issue with the property itself.

Tenants do have a role to play in using the home in a reasonable way. For example, they can help by using extractor fans, opening windows where safe and practical, keeping trickle vents open, covering pans when cooking, and avoiding drying large amounts of washing indoors without ventilation.

However, landlords should be careful not to assume that damp and mould are simply down to tenant behaviour. Current GOV.UK guidance is clear that landlords should identify and tackle the underlying causes of damp and mould, including building deficiencies, inadequate ventilation, and condensation. (Gov.UK)

This is especially important if the property is difficult to heat, poorly insulated, has no effective ventilation, or has ongoing repair issues. In these cases, asking the tenant to open a window will not be enough.

How can I prevent mould?

There are a few things that a landlord can do to prevent mould before it becomes a problem. It all boils down to moisture control and maintenance. In terms of maintenance, the roof, guttering, and drains all need to be in good working order, along with tight and secure window frames to ensure that rain doesn’t seep in. You should make sure the property is as mould-resistant as possible before a tenant moves in. Ensure that the house is equipped with extractor fans and vents for proper ventilation and conduct regular checks of the house, keeping an eye out for suspicious damp patches and areas where there’s frequent condensation.

Before a tenancy starts, it is also worth checking that bathrooms and kitchens have working ventilation, that trickle vents have not been blocked, and that any previous damp patches have been properly investigated rather than just painted over.

Day to day, there’s a lot that your tenant can do to minimise the risk of mould, as many of their regular living activities will create moisture, such as cooking, showering and boiling the kettle. It’s vital to educate them, if they aren’t already aware, of the little things they can do to help. Encourage them to contact you as soon as they suspect any damp or mould in the property. Ask them to dry any wet areas immediately in the event of spills and make sure they keep the rooms well-circulated by keeping adjoining doors open and opening windows for small periods each day. Make sure furniture sits away from the walls, letting fresh air in to reduce moisture.

It is also worth making tenants feel comfortable reporting damp or mould early. Some tenants may worry that they will be blamed, charged, or asked to leave, so clear communication can make a big difference. The sooner a problem is reported, the easier it usually is to fix.

If you’ve done everything you can to reduce the risk of mould, yet your tenant is doing all the wrong things and creating the problem, then this is going to cause tension and raise question marks when deciding who’ll be covering the repair costs…

That said, landlords should avoid jumping straight to blame. If mould is reported, it is best to inspect the property, keep a written record, take photographs where needed, and consider whether there is an underlying repair, insulation, or ventilation issue. You should also deal with both the visible mould and the root cause. Cleaning mould from a wall may only be a short-term fix if the real issue is a leaking gutter, a failed extractor fan, or a cold external wall.

For a more detailed guide, read our article on what landlords should do to stop mould.

What about Awaab’s Law?

Damp and mould have become a much higher-profile issue in recent years, particularly following the tragic death of Awaab Ishak, who died after prolonged exposure to mould in his home.

Awaab’s Law currently applies to social housing, setting strict timescales for social landlords to investigate and fix serious hazards. The government has also said it intends to extend similar protections to the private rented sector, although the details and timing for private landlords remain subject to consultation and further regulations. (Gov.UK)

For private landlords, the important takeaway is not to wait for future rules before taking damp and mould seriously. Existing housing, repair, and safety duties already mean landlords should deal with hazards and property defects properly.

The most important piece of advice we can give you is not to ignore a damp or mould issue. Your tenant could claim against you for compensation, as it can affect their physical and mental health. If you do find yourself faced with a mould problem, it’s best to leave it to the professionals. If it’s only a small area, you could DIY a removal job, but do your research and don’t do anything without goggles, long rubber gloves, and a mask for your nose and mouth!

The causes of mould are not always straightforward. Sometimes the issue is linked to everyday condensation, but it can also be the result of leaks, poor ventilation, failed insulation, rising damp, or other defects in the property. So, when asking what the main causes of mould are, the simple answer is excess moisture. The more important question is where that moisture is coming from, and what needs to be done to stop it from coming back.

If you’re a landlord with more queries about your rental property, visit our advice centre. We have a range of resources that answer popular questions in the sector. At CIA Landlords, we also offer landlord insurance. This can protect you in the event of loss of rent, theft, fire and more – so make sure you take a look through our policies on offer. To find out more, contact our friendly team.