Indoor Cultures - Tackling Mould

When we carry out surveys on traditional buildings, we often encounter mould growing in parts of the building interior. In fact, we almost always encounter mould growth in parts of the building interior. Usually, where alterations or “improvements” have been carried out in the past, especially those where insulation has been added.

The presence of mould in a property can sometimes induce a sense of panic!


Mould growth on attic timbers


The link between dampness and mould is well known, so you may be worried about the condition of the building fabric.  The use of terms like “Toxic Black Mould” by the media, convey any easy to understand message, ensuring that everyone is also alert to the potential health impacts of mould. These range from asthma to Acute Idiopathic Pulmonary Haemorrhage (AIPH) which causes bleeding of the lungs.


Health Issues

Before we get to carried away, it is important to understand that mould spores are floating in the atmosphere everywhere. You are breathing them in right now. Unless you are in a sterile environment (such as a hospital operating room) you’re breathing mould spores.

In the early 1500’s, a Swiss doctor, Paracelsus, wrote, “all substances are poisons; there is none which is not a poison, the right dose differentiates a poison from a remedy.” To illustrate this point one of the most common mould type in buildings is penicillin, which is one of our most important medicines and antibiotics. However, you also need to consider that uncontrolled growth of penicillin in a building could be health problems for its occupants. The spores may have little effect on some people, but others can have a severe reaction to a particular type of mould, even in low levels.

Trapped in rooms or internal attic spaces, the concentration of mould spores can increase considerably. Assessing the impact of mould on the health of building occupants would need to consider the type of mould, its concentration and the level of exposure that individuals are likely to receive.

As well as the health risks associated with mould, it is an indicator of problems within the building, which will accelerate the deterioration of the building fabric. If ignored, this could eventually result in the need for expensive repairs.

Tackling the mould growth will not only be good for your health, it will be good for your building.


Mould in shower room MAAC Studio Conservation Architects


The Cause

In order to grow inside, mould requires some key conditions to be present. It needs;

  • a food source,
  • oxygen and
  • warmth

The first thing you may be surprised to know that it does not require condensation to be present. We often associate condensation with water running down the surface of cold materials, but this is an extreme condition. Long before you reach this point, the moisture level within building materials that may appear dry, will be slowly rising. A moisture level only slightly above the norm is enough for mould.

Secondly, the mould needs a food source. Organic materials like timber, wood fibres in insulation are ideal.

Finally, we often associate mould growth with cold surfaces, but it actually requires warmth. The surface temperature of the material needs to be above 13 degrees Celcius.


Tackling Mould

There are various treatments available. These will remove mould and prevent it from returning by coating the surfaces of the materials where it is growing with chemicals. While this may deal with your health concerns, it does not resolve the underlying building problem. Whether or not there is a health impact, the presence of mould is an indication that there is a more serious problem within the building fabric. This needs to be addressed, or you may find that your property suffers serious and extensive damaged.

Solve the fabric problem and you will solve the mould problem.

To tackle mould, we need to tackle the cause of the mould. Since we cannot remove the oxygen and we want to live and work in warm buildings, we must focus attention on the remaining conditions that are required by mould in order to grow; moisture levels and food sources.

Ventilation is a key method of reducing moisture build up in materials.

Moisture levels and temperature have a very close relationship to each other. The warmer your house, the higher the potential moisture level and the greater the need for ventilation. When fresh air drawn into a property, its moisture level suddenly drops artificially as it is warmed up. In order to return to a balance, it needs to absorb moisture from its surroundings, causing materials to dry out as they give any moisture they may have. Continually drawing in a controlled level of fresh air ensures you property is dry. People don’t like draughts, so ventilation needs to be designed carefully, or it will be blocked up. It also needs to reach all areas. Spaces below beds, at the back of furniture in spare rooms, or attic spaces can trap pockets of stagnant air, causing moisture levels to rise.

In addition to ventilation, our other option is remove the sources of food that mould needs.

Your choice of building materials will play a part in either helping to eliminate mould, or exacerbating a problem. Some forms of insulation, such as phenolic foam offer no food for mould, but it doesn’t breathe, so needs to be used carefully to avoid moisture problems elsewhere. Wood fibre and mineral wool insulation breathes but are a good food source. The modern plasterboard contains gypsum which is a food source for mould and is also wrapped in paper another foodstuff.

Traditional lime plaster, is highly alkaline has excellent mould inhibiting properties. It is also highly breathable, allowing moisture to evaporate quickly.

Your architect will be able to advise on the various methods for analysing building your fabric and identifying areas of potential risk.


Surface Mould in Attic Space MAAC Studio conservation architect Inverness


Planning “Improvements”

The relationship between insulation and ventilation is of critical importance when planning improvements to your property.

Traditional buildings, were built in a manner that was inherently resistant to mould growth, but the impact of changes and alterations that are not based on a thorough understanding the way these older properties work, can be very detrimental.

Before starting, you need a complete understanding of your property, so arrange a traditional building health check.

When you understand the condition your property is currently in, you can then move the next step and develop a whole building approach to improvement. If you focus on one element, such as windows and ignore the effect this may have on others, you make change the way your property works, increasing the risk of problems in other areas.


Penicillium on the back of furniture


Types of Mould

There are many, many, mould types present in buildings. Their proper identification and classification requires a laboratory and their health effects depend on the concentration of spores and vulnerability of building occupants. It is impossible to give anything more than the briefest of introductions to what you might find. If you have concerns, it is important to get expert advice.

Penicillium is the most common mould found indoors. It is a light green colour. It can occur indoors even if the relative humidity is low, as long as there is sufficient moisture available on a given surface. It tends to prefer cooler temperatures which might be found in storage areas or sheds. It grows on food, timber leather and can be often be found on the back of wooden furniture stored in cold area.

Black mould is a generic name used to describe various kinds of mould.

Cladosporium is a commonly occurring mould type that is black or olive green in colour. They grow in areas of intermittent damp or high humidity. The fungus will spread across organic materials like paint, wallpaper and plaster. It leaves a lingering damp smell.

The Stachybotrys Chartarum species of mould is also black but much less common than other moulds. It associated with the most severe health impacts.a nd it is this mould that is known as the “toxic” variety. It requires very damp conditions to grow; typically, in warm, humid and damp areas of a property and is restricted to cellulose based materials such as the paper covering of gypsum wall board, on wallpaper and carpets with natural fibres.

Mildew is a surface fungi that can easily be identified as a patch of grey or white fluffy growth that is lying on the surface of a moist area of material like timber or paper.


MAAC studio are accredited conservation architects and principal designers working with traditional buildings throughout Scotland. 

If you need independent advice give us a call ?