min read

Tom Entwistle's ultimate guide to: Dampness, Condensation and Mould

condensation mould|condensation


It's that time of year landlords dread: their tenant complains about dampness and black mould in their home, and they expect the landlord to do something about it, but what?

Nobody wants to live in a damp home. It causes mould on walls, furniture, bedding and clothes and it creates an unhealthy environment.

There are three main causes of damp:

(1) rising damp which emanates from the foundations up and shows itself on the lower parts of ground floor walls , skirting, floorboards etc., and if left unchecked can lead to wet and dry rot in floor timbers.

(2) penetrating damp which result from faults in the structure of the building, leaking roofs, gutters, downpipes, window frames etc. This can also damage the fabric of the building if left unchecked and again can result is wet and dry rot.

(3) condensation, perhaps the most common cause of black mould and mildew on fabrics, clothes, walls and wallpaper.  

Points one and two are problems for the landlord to see to without delay. The landlord is under a legal obligation to maintain the fabric of the building which provides a safe, warm and dry home.

Condensation is slightly different because although it can be caused by problems with the building, it is also something that may be caused by the actions of the occupants ' the tenants. That's why it is so difficult to deal with for landlords.

Older buildings suffer most

Older buildings with limited insulation are more susceptible to condensation than modern fully insulated buildings, but any building can be affected if the conditions are right, even newly built ones. In fact, new-builds are often more like an air tight box; there are fewer draughts so poorly ventilated because of this.

Condensation occurs when moist air comes into contact with a cold surface like a wall, window, mirror, wallpaper, clothing and fabrics etc. Warm air rises so it is more often the tops of walls and ceilings which are affected, usually in upstairs rooms which tend to be less well heated like bathrooms and bedrooms.

The warm moisture-holding air can't hold the moisture when it hits cold surfaces and it deposits tiny drops of water on these surfaces. When there is still air, like the corners of rooms, behind furniture or inside wardrobes the problem will be worse.

The usual causes are when steam is produced from cooking, drying clothes on radiators, baths and showers, where the steam produced is not immediate vented to the outside and is allowed to circulated around the house.  

Condensation and black mould is unsightly and can cause health problems, so tenants may need to be 'educated' as to methods of preventing condensation:

How to reduce damp and condensation in the home, what the tenant can do:

(1) Produce less moisture and make sure it is vented to the outside.

Simple things will make a big difference, like opening a window when cooking and showering, keeping the doors closed to prevent moisture spread throughout the house, keeping the lids on pans when cooking and using cooker extractor fans, drying clothes outside (and especially not on radiators), venting tumble dryers to the outside. Paraffin heaters or flue-less bottled gas heaters produce a lot of excess moisture.

Landlords can help by providing automatic ventilation fans in kitchens and bathrooms. These open and come on automatically when they sense high humidity, steam / moisture.

(2) Maintain a reasonable level of heat.

A cold house leads to cold surfaces which condense and absorb moisture. By maintaining a good level of heating in the home the surfaces will not condense and absorb the moisture and therefore there will be little on no condensation. Heating, coupled with good ventilation at the source of the moisture will prevent most causes of condensation completely.

Invariably, in bad cases of condensation the tenant is trying to save on heating bills, and because the house is so cold the tenant will be reluctant to ventilate. I've even seen cases where ventilation ducts and trickle vents are blocked to prevent drafts because the house is so cold. This coupled with drying clothes indoors and all the other sources of moisture generation leads to a vicious circle of more cold walls, more moisture penetration, even colder walls and more condensation.

Once this cycle is started the fabric of the building absorbs the moisture and in extreme cases timber, plaster and masonry are damaged permanently. Also, once the mould spores are established the black mould will always return every time the right conditions are present, even when deep cleaned.

How to reduce damp and condensation in the home, what the landlord can do:

(1) Make sure the building is free from external defects, rising and penetration damp.

(2) Make sure the home is insulated to modern standards meeting the latest Energy Efficiency Standard of at least E or C if possible as C is likely to be mandated eventually.

(3) Make sure the heating system is up to standard and is reasonably efficient to run otherwise tenants will avoid using energy if it is costing them too much.

(4) Provide extractor fans which are an effective way to get rid of moist air and steam in kitchens and bathrooms so that less condensation forms. Most modern homes have extractor fans which are automatic or run continuously with the lights, fitted in the ceilings of kitchen, bath and shower rooms and kitchen cooker hoods.

(5) Provide door closers to keep moisture confined to where it is generated.

(6) In extreme cases think about a fully forced heat exchanger ventilation system, where an air pump in the attic continually circulates the air.

(7) Talk to your tenants about what to do in winter to prevent water busts and condensation and provide written information to back this up, educate your tenants as to how they can minimise winter problems.

How to get rid of black mould

If the home is already affected by black mould after a long period of condensation build-up, it needs to be properly cleaned with a spray containing bleach. Wear a mask to prevent inhaling mould spores which are dangerous to health and gloves to protect your hands. After the area is dry it should be sprayed with an anti-fungal wash and allow that to dry again - follow the manufacturer's instructions.

You can also treat the affected areas with mould-resistant paint, available from most major hardware stores, but this should not be necessary if the area is properly cleaned.

Images of black and unsightly mould in the corners of rooms are always the focus of TV documentaries. These reports on these kinds of housing conditions that tenants are living in almost always the blame the landlord. A proper understanding of condensation and mould and its causes however shows that very often it's caused by the lifestyle of the tenants, and it is only the tenants who can do something about it.

A typical scenario goes like this:

'I have noticed black patches on the wall paper, mould on my clothes in the wardrobe and a damp musty smell throughout the house, particularly upstairs. Landlord, what are you going to do about it, are you going to compensate me for the damage to my clothes?

'I've asked a damp specialist who tells me there's definitely damp in here, so it's not just me saying this, can you get someone in to deal with it right away?'

A few points to consider if you are faced with this:

Condensation, damp and mould is a very complex issue and it's not always obvious what the cause is and who should be held responsible. You should avoid jumping to conclusions until you have fully investigated.

Also, it must be born in mind that advisors on damp often have a vested interest in finding an issue - like asking a hairdresser if you need a haircut!

If it comes to legal action and blame, enforcement has just as often been against the tenant as it has been against the landlord, when all the evidence has been exposed.

Unless a specific cause can be identified for the dampness such as leaking roof, walls, gutters, drains, water pipes or rising damp, the black mould is more often than not caused by condensation of air born water vapour.

Condensation in turn is sometimes caused be inadequacies in the building construction, such as poor ventilation, little or no insulation and an inadequate heating system.

Older properties are more susceptible because they generally require more heating, being solid walls they have no cavity wall insulation, and therefore suffer greater heat loss.

Of all the residential buildings in England with an attic, one-third have no attic insulation at all.

If you are in dispute, carry out a thorough investigation and if necessary a temperature monitor can be installed to check the average level of heating being applied by the tenant over a period. The home heating should not fall below 18 degrees.

Its a good idea to always ask tenants to complete a satisfaction survey when they leave. If the property has never had a condensation problem reported before you have some excellent evidence to show that it is unlikely the building is at fault.

High Energy Costs

In these days of high energy costs and pending regulation on rental housing condition, it is more important than ever to ensure that your rental properties are well insulated, they provide good ventilation systems in kitchens and bathrooms and your heating system is efficient and as economical as possible to run.

This article updated October 2022

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