Helpful Tips Property Management RPI

RPI: The black stuff…(Mould)

residential property investor rpi
Sally Walmsley
Written by Sally Walmsley

Fighting the common enemy of both tenants and landlords – mould

At this time of year, damp and mould can be common problems in rental properties.

Depressing and potentially unhealthy for tenants, mould is categorised by the World Health Organisation as being a risk to health.

Damp and mould are often perceived by landlords as notoriously difficult to deal with, particularly when the tenants are still in situ. A number of landlords would prefer to wait to tackle the problem in between tenancies.

However, the so-called retaliatory eviction legislation introduced last October could change this.

The rules now mean that a Section 21 notice cannot be served for at least six months when a complaint is made about the condition of a property and that complaint is accepted as valid by the local authority.

Because damp and mould are so commonplace, they are likely to be the cause of complaints and, if so, then under the legislation, landlords should take corrective action within a reasonable timeframe.

Landlords should bear in mind that condensation and mould growth are not problems that can be treated retrospectively with sprays or redecoration – they will simply continue to occur.

Without preventative action being taken, the situation only gets worse, causing damage to the fabric of the building as well as potential harm to the occupants’ health.


Damp and mould occur when there is inadequate ventilation in a home – often leading to landlords’ suspicions that it is the tenant’s own lifestyle that is the root cause of the problem.

Whereas at one time tenants were simply told to ‘open the windows’, there are a number of reasons why this is not the answer for many people.

The very young need warmth, and old people are advised to live in a constant temperature of around 18-21o C in order to remain healthy.

Opening windows when the temperature is much lower for any period of time could cause a number of health issues such as pneumonia and hypothermia.

There can also be issues with outdoor pollution or noise, not to mention energy efficiency and security.


Condensation in a home is a sure sign that a property suffers from poor indoor air quality. Recent studies show that 58% of householders experience condensation and over a fifth say they have a problem with mould in their homes.

The situation is worse in the winter months because humidity inside the home is higher (as windows are kept closed to conserve heat) and there is a larger differential between indoor and outside temperatures, meaning more cold surfaces for condensation to form.

Condensation is most noticeable in kitchens and bathrooms where most of the moisture is generated. However, it is also very common to find mould and condensation issues in bedrooms, as moisture migrates throughout the property.

The situation is even worse when dwellings have internal bathrooms with no windows, as is often the case in flats, which can be prone to serious condensation, especially if an extractor fan is blocked or switched off.

High humidity provides a haven for household dust mites and their detritus which flourish in damp, mouldy conditions. They can live in bedding, carpets and other soft furnishings in homes that do not have adequate ventilation.

When this detritus comes into contact with skin or is inhaled, it can cause allergic reactions such as asthma or dermatological conditions.

Low-level background ventilation to a property is a solution to consider, as it avoids heat loss and draughts.

At the very least, ventilation should be fitted in kitchens and bathrooms, but as moisture spreads to bedrooms, occupants can often find mould spores growing on walls, around windows and in cupboards and wardrobes.

Positive Input Ventilation systems

Whole house ventilation systems such as Positive Input Ventilation are becoming more popular as they provide a long-term solution to the problem.

PIV systems are not new, having been developed in the 1970s.

They work by drawing in fresh, filtered, clean air from the outside and gently ventilating the home from a central position, usually in the loft, above a landing in a house, or a central hallway in a flat or bungalow.

The systems aim to dilute moisture laden air, displacing it and replacing it to control humidity levels between 45–60% where condensation does not form.

But do they work?

The Building Research Establishment looked at a system installed in an unoccupied test house on its own site, plus installations in 16 occupied homes in Merthyr Tydfil and Aldershot.

The BRE’s tests found that the system was effective in reducing humidity levels by 10% in the test house.

In the 16 occupied homes, it found that the systems were not consistently effective but, interestingly, was effective in the most humid houses.

The trial also noted that the “occupants were more enthusiastic about the effectiveness of input ventilation than the results would suggest. Those who previously had the highest humidity in their houses were the most impressed.

“Some occupants also claimed relief from severe respiratory illness but these claims could not be substantiated in this project.”

According to the BRE, installing a low-energy PIV system will not directly save any energy, but may give an energy saving compared with a conventional extract system. This is because a PIV system usually takes its air from the roof space, where temperatures are higher than outside.

PIV systems are made by a number of manufacturers, who claim that the systems are easy to install in both newbuild and retrofit situations, and are extremely cheap to run.


Rebecca McLean, marketing director at one manufacturer, EnviroVent, says: “The aim with PIV systems is to deliver adequate whole house ventilation rates, rather than simply meeting minimum standards.

“Where landlords choose to invest in ventilation systems, the direct results have been fewer call-outs to their maintenance teams, better relationships with tenants and a positive impact on people’s health.

“The problem with some extractor fans is that they can become blocked, switched off or isolated by tenants, leaving them inoperable.

“Our PIV systems are designed to be tamper-proof. What’s more, these ‘fit and forget’ systems produce little noise and have extremely low energy usage.”

Tenants must play their part

However, she cautions that tenants should still play a part in reducing condensation. She says: “Landlords need to continue to work closely with tenants to remind them how lifestyle choices can affect moisture levels in the home.

“For example, practical ways to reduce moisture include covering pans when cooking, avoiding drying clothes indoors whenever possible, ventilating the tumble dryer to the outside, and also making sure they do not block extract fans or indeed not switching them off.”

So what type of action should a landlord take when a tenant complains about mould? Moisture readings should be taken in the property and landlords should then consider either single room extract fans or ventilating the whole house.

This action needs to be taken within a reasonable timeframe if a tenant has complained.

McLean adds: “When ventilation systems such as PIV are fitted, it is important to explain to the tenant its purpose and how to use it correctly. Tenants should also be made aware that the cost of running the extractor is minimal.

“One of our landlord purchasers, Charles Robertson, says that after two weeks his tenants reported a significant reduction in condensation and an improvement in general environment in the house after one of our PIV systems was fitted.

“Our research with customers has demonstrated that in 85% of cases, households report an improvement in air quality and a reduction in condensation issues within two weeks.”


Be very careful about cleaning mould – top tips for mould cleaning:

  1. If the worst has happened and those dreaded mould spores have appeared, do not assume that either you or your tenant can simply clean them off.
  2. Official NHS advice is only to attempt a DIY clean if you are sure the mould is covered by condensation (and not, for example, by contaminated water), and only if it covers an area of less than one square metre.
  3. For larger areas of mould, you should call in professional cleaning companies.
  4. If you do clean small areas, you should wear goggles, long rubber gloves and a mask that covers your mouth and nose.
  5. You should open the windows in the room, but keep doors closed to prevent spores spreading to other areas of the house.
  6. Have a plastic bag ready to take away any soft furnishings, clothes and soft toys that are mouldy.
  7. Soft furnishings should be shampooed and clothes professionally dry-cleaned.
  8. Fill a bucket with water and some mild detergent, such as washing-up liquid or a soap used for hand-washing clothes.
  9. Use a rag dipped in the soapy water to carefully wipe the mould off the wall. Be careful not to brush it, as this can release mould spores.
  10. When you’ve finished, use a dry rag to remove the moisture from the wall. Afterwards, put the rags in a plastic bag and throw them away.
  11. All the surfaces in the room should be thoroughly cleaned by either wet-wiping or vacuuming to remove any spores.


This article is taken from the Residential Property Investor, the RLA’s official members magazine, which is provided free to members. To read more join the RLA here or visit the RPI website here

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About the author

Sally Walmsley

Sally Walmsley

Sally Walmsley is the Magazine and Digital Editor for the NRLA. With 20 years’ experience writing for regional and national newspapers and magazines she is responsible for editing our members' magazine 'Property', producing our articles for our news site, the weekly and monthly bulletins and editorial content for our media partners.


  • Interesting article about condensation. We receive many calls from landlords and tenants often confusing condensation with a rising damp problem. When we are called to survey a property, we may specify a unit such as a PIV, sometimes combined with an extract fan and adding ventilation by perhaps simply unblocking an air brick. In our experience, this provides a highly effective and low cost solution relative to the ongoing stress and redecoration costs condensation and black mould can cause.

  • Great article Sally, very thorough and informative. One quick observation, in my experience, no mechanica/electrical system is tamper proof when in the hands of a vindictive or ill-informed tenant. They will nearly always find a way to turn something off that they think is creating a ‘draft’ or ‘costing too much money’. That said, PIV systems can have dramatic effects and I’m a big supporter of them, in the right environment.

    Landlords do need to make sure they’ve covered off the basics first though, Ive lost count of the number of properties I’ve seen this year already with no source of extraction in bathrooms and kitchens. Moisture extraction at the source of creation is always best and a PIV will need some outlets to continue the circulation process.

    For large areas of mould growth, or neglected properties, professional treatment of the affected areas is a must. A decent firm will always use a variety of professional grade equipment and techniques to safely remove affected materials, clean and repair surfaces and leave the property in a good decorative order.

    Thanks again for a great article!

  • An excellent article – could almost have been written by a professional damp control company…..good to see advice that is positive and correct. I have reservations about the scarey comments abut cleaning mould but these days the ‘better safe than sorry’ culture is rife.

  • I find this article simplistic. How can you praise a system that only tackles the problem by 10%? You need a process or system or product that sorts out the problem.
    Our previous tenant refused point blank to do nothing but dry their all their washed clothes etc on the radiators and would not open any windows, then complained bitterly that they had damp. A specialist confirmed it was self inflicted condensation. They had a window in the bathroom and an extractor in the kitchen and we supplied them with a dehumidifier which they refused point blank to use as they said it consumed electricity. This is the sort of tenant that we require advice how to encourage to behave sensibly. We tried to give them sensible advice, and gave them a copy of all the Advice produced by all the agencies but to no avail.

    • Hi Beryl,
      Thank you for your feedback. This article was from our RPI magazine and was written to raise awareness of Mould. This is a wide-ranging subject and it is difficult to cover all the topic in the space required. If you would like more information on this, you can read our full guide on the RLA website
      Kind regards,

  • Very interesting article and advice. I have been aware of PIV units for a number of years and I have run a small building firm specialising in damp and condensation issues for a number of years and have fitted these for a number of customers. I routinely have them fitted in most of my properties as they are being refurbished aswell. They do assist and have massively reduced the number of calls I receive each winter to no more than a handful. The only problem I have recently experienced though is from a lady who loves living in a particular house and is aware the property suffers from bad condensation problems (she has owner occupier friends in the same street that state they suffer aswell). She knows she has a PIV installed and knows what it is designed to do. However, as it is situated in the landing and blows a stream of cool air in, the family comment on it and so she closes the vent opening so no fresh air can enter! When I brought this to her attention during a recent visit she said she wasn’t concerned about the mould spores because in her opinion as soon as the weather warms she opens her windows and doors, cleans it all up using water and strong bleach and they all go again! She was fully aware the problem source was her families lifestyle, wasn’t concerned and would prefer the mould during the winter as opposed to cold air being blown in to minimise the problem via the PIV. What can you do??

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