Condensation & Mould – What to do! (Part 1)

Condensation & Mould – What to do! (Part 1)


Mould has recently, for very unfortunate circumstances, taken media centre stage again and it is timely reminder for PRS (Private Rental Sector) landlords to re-evaluate their properties and the tenants they have living within them. Mould is one of the most listed and important points out of the twenty nine in the Housing Health Safety Rating System, which the council will refer to if asked to inspect a property.


Mould has always been an issue in property for centuries, but in the modern age as we strive for energy efficiency and zero carbon emissions, we find ourselves at an uneasy crossroads; particularly crystalized by the current high cost of energy and affordability. The modern house with double glazing and insulation, is rarely intended to be naturally ventilated and has become a virtual hermetically sealed box, into which, landlords install tenants who have varied lifestyles and expectations. The fundamentals for causing mould have never really changed, rather they have just mutated from what was originally seen as the main causes to a plethora of other additional reasons. This can lead in many cases of mould to the cause actually being described as “tenant behaviour”, which in turn can cause a dispute.


To this end, it is important that both parties having a decent understanding of what causes mould in a modern house, so some of the future problems can be avoided or addressed. Mould growth normally occurs when condensation turns to water droplets  which happens when warm air hits a cold surface, causing surface dampness. This issue is commonly caused by contrasting internal room temperatures due primarily to insufficient heating in addition to there being a lack of adequate ventilation. With the current energy crisis, there is a risk that if houses become colder than usual, due the heating being switched off, condensation will significantly increase.


If condensation is not addressed, this can lead to problems such as mould, which is a fungus that grows on wet surfaces and is routinely caused by excess moisture. This is normally a result of condensation where walls and windows are cold and there is high moisture content in the air.


Condensation is the most studied cause, but there are many cases where damage or decay has occurred to the structure of the property and this can lead to penetrating leaks which can cause damp. Likewise, a defective damp proof course will allow water ingress, leading to rising damp that can occur in basements and ground floors, however this does not generally result in growth of black mould.


Damp and mould in residential properties can lead to health issues and exacerbate existing allergies and respiratory conditions. There are simple steps that both tenants and landlords can take to prevent both, which involve both parties having an understanding of their responsibilities and how daily routines can contribute to them around the property as well as how to prevent these issues arising in the first place.


A simple guide should be created and given to the tenants at the start of the tenancy so they understand their responsibilities. Below is a rough guide which is not fully comprehensive:

Using an appropriate cleaning product at regular intervals.

When cooking, putting lids on pans to prevent excess moisture going into the air.

Using the cooker hood/extractor fan when cooking

Making sure the bathroom air extractor fan is not switched off at the isolation switch and is left on when showering and preferably for a further ten minutes afterwards!

Not hanging wet clothes on radiators nor drying clothes indoors at all, if practical. Where there is no alternative, a room should be chosen with good ventilation, a drying rack being used and the room door closed so that the moist air remains in only that room and is not spread around the property. If natural ventilation is not a viable option, using a de-humidifier can work well, but the container will need regular checking and emptying out.

Running a reasonable amount of heating in the property; because homes alternating between cold and hot is very bad for the structure of the building.

Checking where trickle vents are provided on UPVC windows, that these are kept open.

Ensuring that furniture is not preventing air flow by being placed against walls or in front of radiators.


Landlords can also need to be proactive to this problem by:

Decorating properties using anti-mould paint

Inspecting the condition of the property at regular intervals.

Responding promptly to any concerns raised by the tenant and investigating the issue.

Ensuring appropriate insulation and draught proofing are in place and in the case of the former, when insulation roof spaces, the insulation needs to go to the very edges of the roof space and not leave a small gap with no covering. If this area is left, it is very likely that mould will appear on the ceiling in the same place in the room below.

Ensuring that vents and fans are working – if uncertain clarify with the tenant.

Ensuring that tenants know how to use the heating system and thermostat controls efficiently – easy to follow notes should be issued as modern boilers and heating systems can appear to be very complicated these days.

Repairing any leaks or plumbing issues promptly, and not ignoring the tenants cry for help!


Having a good understanding of condensation and what to expect is essential in helping to combat this age old problem. If Landlords are proactive to the property type they are letting out and Tenants are aware of their actions, a lot of the current mould problems can be lessened if not eliminated!