Mould, a consequence of defect or use?

Mould in homes can be due to defects such as slow leaks, or rising damp, but more often than not, it is a consequence of condensation.

After talking to clients, landlords, tenants, friends and family, we have come to the appreciation that mould, and specifically ‘condensation’ derived mould, is not always well understood. There seems to be a natural tendency to assume that mould always occurs due to a defect in the building and less of an appreciation that mould is often preventable and manageable if we adjust our usage habits.

Specifically in the case of older buildings, there is often a need to adjust the way we use them to offset performance limitations of the building that may simply be a consequence of the age and method of construction typical for that building vintage.

In this article, we will explain what we mean and useful processes to be aware of.

Are mould problems likely to increase?

The cost of heating homes has dramatically increased in recent years, meaning some households might have or are considering cutting back on their heating use, either by reducing the thermostat setting or by decreasing the time the home is heated.

Mould needs ‘moisture’ (damp), a ‘substrate’ (surface) and ‘nutrients’ (food) to grow.

Most substrates like timber or wallpaper have nutrients within the substrate. However, with windows or carpet, for example, it may be the dust and other contaminants which is providing the nutrients. Mould can even metabolise some paints.

Buildings are abundant in materials that can act as substrates and provide nutrients, and so there are few scenarios in which targeting these factors makes sense. For example, even if Wolves are tiled with porcelain tiles and ceilings are painted with mould-resistant paint. These surfaces will still act as substrates and any dust that might cling to the surface when condensation occurs will provide the nutrients. That said, cleaning of such surfaces, is still an important mould management strategy that applies to almost all homes. For example, condensation and dust typically occurs in cold areas in bathrooms, such as around water systems, and to window frames, and if these are not cleaned regularly mould will almost always grow. however, these are typically circumstances where condensation is unavoidable, and for nearly all other circumstances, preventing the damp or condensation is the correct strategy. This is why we should concentrate on removing the ‘dampness’ in order to get rid of mould.

The point of this post to encourage readers to consider the causes of damp in a bit more detail.

If condensation (in absence of building defects) is the leading cause of damp, and damp is the leading cause of mould; then we need to understand why condensation is occurring in order to prevent it.

For Condensation to occur, you need two main conditions;

1) Relatively high humidity and,

2) Relatively cold temperature.

The ‘relatively’ part is important.

If air with the right humidity meets a surface with a low enough temperature, you get condensation. This is known as a dew-point. The dew-point can vary. If the humidity is really high, the temperature doesn’t need to be so cold (think of the droplets of water that quickly form around a boiling kettle). If the temperature is really cold, the humidity doesn't have to be as high, (think breath on a cold window).

The reason that the moisture around your kettle doesn’t result in mould is that it quickly dries out.

There are many other sources of moisture or humidity in a home, for example, hot showers, baths, breath, and cooking and there is insufficient ventilation to bring humidity levels back down to normal.

They're also many reasons why some parts of your house might be relatively cold. For example, rooms with smaller radiators, the corners of rooms where the heating has been turned down, ceiling edges beneath eaves where insulation is not a stick, the inner face of uninsulated walls, around cold water pipes, around coldwater tanks or toilet cisterns, behind furniture or wardrobes that do not get the benefit of heating from radiators, windows that are not warmed by radiators beneath.

If the home user is generating a lot of moisture or humidity so to speak then the cold surfaces do not need to be that cold for condensation and mould to occur. if the home user keeps their property relatively cool or there are spots within it. The humidity does not need to be that high for condensation and mould to occur.

The important thing to remember is that these two factors need to be balanced in order to mitigate mould and on occasion, if the user has not got this strategy quite right and mould starts to grow, it should be cleaned immediately, and the building user should consider whether the strategy can be improved or if improvements to the building are appropriate. This might involve the help of a surveyor.

We will describe some typical examples.

Windows

Windows are a cold bridge to the outside environment and will often ‘stay’ sufficiently cold for condensation to form and persist in scenarios where there is a lack of heating and any source of humidity. If this condensation is not dried by increased ‘heating’ or is cleaned, it will combine with dust (note what is said about nutrients earlier), and over time mould will grow. This will often happen in bathrooms where the air is more humid, and heating may be less.

The conditions have arisen for condensation and mould by the occupants ‘use’ of the building alone, without any defects in the structure being present.

Why this might get worse with higher heating costs?

Now I invite you to consider a theoretical room in your home. Perhaps it is a first-floor guest bedroom or box room, and the radiator is turned down or off. You have a wardrobe in the corner and the door is kept shut.

You go about your normal activities, like using the shower, cooking; you have friends and family over generating lots of moisture from their breath. It’s winter and you are keeping your windows closed and perhaps the extract fans in the kitchen and bathroom are not great.

Moist air (high humidity air) will be diffusing from these parts of the house up into this cold room; in particular, the walls behind the wardrobe may be sufficiently cold for mould to grow.

If your home has solid walls and is uninsulated, mould growth in this room is now a probability.

And it can get worse!

Why adding insulation might make this worse

If a cold house means increased chances of mould, you might take your self to B&Q and buy a few rolls of insulation for the loft. Less heat lost through the roof will mean less mould, you think.

Well, yes. Probably. But moisture is a tricky thing to manage.

Heat rises, correct? And so, does hot moist air from the kitchen and the shower, from the cloths drying on your cloths horse or on the radiator.

This warm moist air will rise up through all parts of your home, passing through gaps in the floor boards, holes in the ceiling where the lights are fitted, up through the loft hatch etc and into your loft.

What you have done now is you have made your roof space even colder and this hot moist air will meet very cold winter air in the loft... A ‘dew point’ is likely to occur.

This would not normally be a problem because the dew would quickly be dried out by the air blowing through the gaps or vents in your loft. Unfortunately, you have recently covered over all of the eaves ventilators with your new insulation.

The next time you take a look in your loft to retrieve the Christmas decorations, you might find that everything is damp and has gone mouldy.

At its worst, conditions may even be right for timber decay to occur.

This sounds complicated. What do a I do?

Each building will have its own complexities, cold spots, thermal bridges, and sources of moisture. If you have a severe problem, it is probably a good idea for a professional takes a look for you. This is even more important if you a living amongst mould growth, which is a health hazard.

However, there are some simple things you can do:

A baseline of heating to your home is important and you can also put extra effort into reducing the humidity in the air. That means; opening windows if you need to when you are cooking. Drying cloths outside or with externally ventilated dryers. Take shorter, cooler showers if you want to keep the window closed. If long, hot showers are needed, additional heating and ventilation will be required. Change cooking habits like oven roasting instead of hob boiling or steaming in the winter when it's cold, and you want to limit the amount of time you open the window.

If you see mould start to grow, clean it as soon as you notice it. Wipe down wet windows as a matter of routine.

As we said at the top. Most mould problems are a consequence of how we use our buildings. If you are unsure if this is the case and think you might have a building defect, please give us a call.