Dealing with Damp and Mould in Rental Properties:

Damp and mould in rented properties, what causes it and how can it be prevented

Damp and consequent mould build up in rented properties is often mistakenly attributed (especially by the tenants living there) to structural or other building defects.

However, in most cases, it is quite simply due to tenants failing to adequately ventilate and heat the property.

Edinburgh’s cold, damp climate and large stock of ancient tenements can, of course exacerbate the problem, particularly in the winter months, but in most instances damp and mould are entirely preventable.

That is not to say that damp patches (and mould) aren’t sometimes caused by building defects (compromised damp proofing, roof leaks, overflowing gutters or leaking down pipes, crumbling pointing or render or pipe leaks from within the property of neighbouring properties). However, more frequently damp and mould are entirely preventable.

What is “damp” and where does the black mould come from?

Black mould forms as a direct result of condensation, which occurs when warm, moisture-laden air meets a cold surface. As the air cools, it loses its ability to hold moisture, causing water droplets to form on walls, windows, and ceilings.

This excess moisture creates the perfect breeding ground for mould spores, which are naturally present in the air. When these spores land on damp surfaces, they begin to grow, spreading rapidly in areas with poor ventilation and insufficient heating.

Common locations for black mould include window frames, corners of rooms, and behind furniture where airflow is restricted, making it difficult for moisture to evaporate.

What do we mean by lack of ventilation and heating?

1. Lack of Ventilation

Quite simply tenants don’t want to let the cold, damp (bracing!) Scottish air in and so often fail to open windows regularly. They will often also close trickle vents in windows, the very things that are designed to help ventilation.

This prevents moisture-laden air – that builds up from every day living (breathing, cooking, showering, clothes drying) – from escaping.

This is particularly common in:

• Bedrooms, where people sleep with windows tightly shut, causing humidity to rise.
• Bathrooms, where steam from showers is not properly expelled, leading to condensation build-up on cold surfaces such as windows or tiles.
• Kitchens, where cooking creates high levels of condensation, especially when extractor fans are not used correctly or are absent
• Living rooms, a favourite spot for clothes drying.

In many Nordic countries or countries in main land Europe it’s common practice to fling open windows each morning for 30 minutes and hang duvets out of them. This, practice, changes the air inside from moist air built up over night to the drier air from outside. But, to say the least, this is not common in Scotland.

2. Inadequate Heating

Heating concerns are also a major factor.

Under the Tolerable Standard Legislation brought in March 2024 (Read more here) Landlords do have an obligation to provide a heating system capable of maintaining 21°C in one room and 18°C elsewhere when the outside temperature is -1°C.

However, many tenants may limit the time they have the heating on due to concerns over high energy costs. This leaves walls cold and more prone to condensation. This is especially problematic in older Edinburgh properties with thick stone walls, which take a long time to heat up and so stay cold even though the air inside becomes warmer (and so able to hold more moisture). The colder walls then provide a prime surface for moisture in the air to condense, leading to mould growth.

Additionally, the common practice in UK homes of turning heating on in the mornings and evenings and off over-night and during the day generates ideal conditions for warm moisture laden air to condense on cold and cooling surfaces. These inconsistent heating patterns, turning the heating on for short bursts rather than maintaining a steady temperature, can make the problem worse by regularly providing the cold surfaces that encourage condensation.

Why Winter Makes the Problem Worse

Winter exacerbates damp problems for three main reasons:

1. Reduced Ventilation: Tenants are even less likely to open windows in colder months, leading to stagnant, moisture-heavy air inside the property. The reluctance to let in cold air further increases humidity levels inside the home.

2. Colder External Walls: As outdoor temperatures drop, the external walls of properties become colder. When warm, humid indoor air comes into contact with these cold surfaces, condensation forms more readily, leading to damp patches and mould. This is especially problematic in north-facing rooms and walls that receive less sunlight and so take longer to warm up.

3. Increased Moisture Production: People spend more time indoors during winter, leading to increased moisture from breathing, cooking, and washing.

The combination of all these factors creates the ideal conditions for damp and mould to thrive.

Landlord Responsibilities and Tenant Accountability

As the Repairing Standard Legislation makes plain Landlords are legally required to provide wind and water tight properties (Read more here), and then can take proactive steps to help manage condensation in a property. However, it is tenants that really have primary responsibility to prevent damp and mould build up.

To ensure proper accountability:

Tenancy Agreements Should Include Clauses on Heating & Ventilation

Landlords should explicitly state (and it is explicitly stated PRS Tenancy Agreement from Scot Govt) in the  in tenancy agreements that tenants are required to heat and ventilate the property adequately. Failure to do so should be considered a breach of tenancy obligations.

Provide Guidance on Best Practices

Educating tenants on the importance of good ventilation and heating can help reduce damp-related issues. Providing an information sheet on managing moisture, including the importance of using extractor fans and leaving trickle vents open, can make a significant difference.

Deposit Deductions for Damp-Related Damage

If a tenant’s failure to heat or ventilate a property leads to significant mould growth or damage requiring redecoration, the cost of repairs can justifiably be deducted from their deposit. Scottish case law supports landlords in such claims—see [Scottish Landlords Association (https://www.scottishlandlords.com/ ) for guidance on relevant cases.

We would recommend that “Failure to adequately heat and ventilate a property” is also included in the prescribed information on a Document 42f when this is provided to tenants i.e. state that it is a circumstance under which deductions from a deposit will be made.

Prevention better than a cure; practical steps for Landlords to Reduce Damp

Good communication with tenants on the issue of damp and mould is one way to help prevent it becoming an issue. There are though also some physical measures that can be taken in the property:

Investing in Mechanical Ventilation Systems:

One of the most effective ways for landlords to combat this issue—particularly in HMOs where multiple occupants generate excess moisture—is installing a Mechanical Ventilation System. At a basic level that’s just ensuring bathroom and kitchens have an “all ways on, trickle with humidistat-controlled boost” extractor fan. But there are more extensive and advanced systems.

These systems continuously extract stale, moisture-laden air while introducing fresh, dry air. Costs for such systems have decreased in recent years, with basic units starting at around £500, while more advanced whole-property solutions can range from £1,500 to £3,500, depending on the size of the property. Additionally, Positive Input Ventilation (PIV) systems, which gently introduce filtered fresh air into the property, can be a cost-effective solution for many landlords.

These figures may seem like a significant investment but will be less costly than the lost rent while a property sits empty and is repainted due to damp and mould build up.

Regular Property Inspections:

As part of regular maintence inspections it’s important to check for early signs of damp, such as condensation on windows, mould in corners, and musty odours.

Encouraging the Use of Dehumidifiers:

We would advise against providing dehumidifiers in a property as a default. For a start if may give the impression to prospective tenants that it is a “damp” property, and, in our experience, tenants are reluctant to use them because they perceive that they consume a lot of electricity.

Better, we would suggest to encourage Tenants to take their responsibilities on themselves and buy and use their own

Applying Anti-Mould Paints:

Treating high-risk areas with specialist anti-mould paints can provide an extra layer of protection.

The Unintended Consequence of Improved Energy Efficiency

Better insulation whether through draft proofing, fitting double glazed windows or adding insulation on external walls should be considered a good thing and will help encourage tenants to keep a property warm by for lowering heating costs.

However, be aware that such measures can inadvertently make properties more susceptible to damp.

Older properties often had natural drafts that provided passive ventilation, but draft proofing modern insulation and double glazing will seal many of these air gaps. While beneficial for energy conservation, this reduces natural airflow, leading to higher moisture retention inside the property. Even more important, therefore, to ensure proper ventilation.

Conclusion

Damp and mould in rented properties are preventable with the right balance of ventilation, heating, and proactive tenancy management. Landlords should include clear tenancy clauses holding tenants accountable for their role in preventing damp while also considering mechanical ventilation solutions for long-term property protection.

Regular inspections, tenant education, and small improvements such as extractor fans and fitting trickle vents in windows can significantly reduce damp-related issues. Ensuring a property remains well-ventilated and heated benefits both landlords and tenants by reducing repair costs and maintaining a healthy living environment.

For further guidance, visit authoritative sources such as:

• Scottish Government Housing Standards
• Edinburgh Council Private Renting Advice

Disclaimer:

This article is for informational purposes only and does not constitute legal advice. HomeForce Property Management (HFPM) makes no representations or warranties regarding the accuracy, completeness, or reliability of the information provided. While every effort has been made to ensure the content is up to date, regulations may change, and interpretations may vary. HFPM is not responsible for any errors, omissions, or actions taken based on this article. Readers are advised to seek independent legal or professional advice regarding their specific circumstances. Links to external websites are provided for convenience and do not imply endorsement or responsibility for their content.