Threats to health and home

Mould is a microscopic fungus that grows in damp places. Black mould is an umbrella term for hundreds of species of fungi that are everywhere on the planet. A rare and toxic micro fungus variety, Stachybotrys chartarum, favours cellulose-rich building materials like wallpaper, gypsum and fibreboard. It can be found in damp or water-damaged buildings.

Medics have long been aware of the link between mould and ill health. Inhaling the invisible spores that mould releases into the air can irritate the lungs and trigger respiratory problems, including coughing, wheezing, sneezing and shortness of breath. People with asthma may be particularly susceptible to mould exposure. Those most at risk from mould include babies, children, the elderly and people with pre-existing respiratory problems and skin diseases.

In addition to its significant health risks, black mould can also impact on the house itself. It can lead to flaky paint, rot, decay and even structural damage over time. Repairs and redecoration will be needed to tackle any damage caused by mould infestation.

What causes black mould in houses and how can it be treated?

Black mould thrives in areas prone to condensation, including around windows. Microscopic black mould spores that are invisible to the eye are in the air we breathe along with dust particles. Problems only occur where the spores land on surfaces prone to excessive moisture and they germinate into black mould.

The presence of water or condensation provides an ideal breeding ground for mould spores. When warm air comes into contact with cold surfaces that are below a temperature known as the dew point, it offloads the water vapour in the form of water droplets. These surfaces can include uninsulated external walls. Older and poorly insulated homes are particularly prone to condensation problems.

Another factor that contributes to black mould growth is poor ventilation. Without adequate airflow, warm air becomes trapped in enclosed spaces, ideal for mould growth. Mould can be found in bedrooms behind heavy furniture, such as wardrobes, next to exterior walls and windows. Air drying clothes indoors, creating excess moisture, can also lead to mould.

Other causes include leaky pipes and roof leaks. Moisture can seep into walls, attics and basements. In severely affected homes, there’s often a damp mouldy smell along with outbreaks of black speckled mould on cold spots, including ceilings and walls.

How do I stop the mould?

Cleaning with a weak bleach solution will usually get rid of visible mould staining. There are also mould sprays that contain a biocide designed to remove mould spores and prevent regrowth. Avoid disturbing the mould with a brush or dry cloth as you’ll disperse the spores. And you don’t want to inhale the spores, bleach or biocide or get them on your skin, so wear PPE (mask and gloves). Wipe off the excess, allow it to dry and then use two coats of paint which should help prevent mould growth recurring. Most of the leading paint manufacturers have anti mould or mould inhibiting paints. Look for those are labelled vapour permeable or breathable. They include ultra-durable and wipeable paints containing vinyl. Avoid anti-damp paints which are designed to stop water coming through the wall as they can trap moisture.

What about dehumidifiers?

The next step is to reduce humidity levels to prevent further mould growth. Dehumidifiers can help, though it’s treating the symptom rather than the cause. If you’re stuck in rented housing and the landlord won’t seek out the source of the damp, these machines can help to reduce the moisture levels and mould infestation. They come in a variety of sizes and need manually emptying when full.

Any severely mould infested material like damp plasterboard or mouldy wallpaper or carpet needs to be stripped out and replaced. After the building materials have had a chance to dry out, relative humidity levels should ideally fall below 65%. A hygrometer can be used to  monitor indoor humidity levels. Relative humidity measures how close the air in a building is to  being saturated, telling you in percentage terms how much water vapour is in the air relative to the maximum possible at that temperature. The dew point is the temperature which the air reaches saturation point and condensation forms.

Tackle the root cause

Cleaning mould and repainting ceiling and walls won’t make it go away forever. You need to tackle the root cause. Is there too little ventilation? Do you use extractor fans or open windows when cooking  or drying clothes indoors? Condensation is usually the culprit. Or is there water seeping into your home through a broken pipe under the floorboards? Broken guttering may also be a factor, causing external walls to become saturated. In some cases,  damp may be rising from the ground up through the walls, which usually creates a tell-tale water mark around the damp patch. This may mean a new damp course is needed.

Penetrating damp is when water has found its way through the structure of the building. Watermarks may appear on walls and ceilings, indicating a problem. When a surveyor checks these areas of the building, they will show high moisture readings. Causes can include blocked gutters, defective pointing, porous masonry, cracked render or a leaking roof. A building surveyor is the best qualified professional to help you identify the root cause of a damp and black mould problem.

How can I ventilate without letting cold air in?

Opening windows can supply a steady stream of fresh air, but they can also let in cold air in winter. Functioning trickle vents above windows and air bricks can also help to reduce risks of mould, damp and condensation problems.

Modern extractor fans are particularly effective in kitchens, bathrooms and utility rooms.  Humidistat fans – fans with an in-built humidity sensor – can have a role to play. Instead of being linked to your light switch and timer, the fan automatically switches on when it detects humidity levels increase above a preset level. This can be effective for a single room, for example a bedroom. These are also heat recovery extractor (humidistat) fans. For instance, the Kair heat recovery fan claims to save up to 86% heat recovered from extracted air. According to the manufacturer, this means even in cold winter weather the incoming clean air will remain at almost the same room temperature, reducing heat loss.

If you are planning an eco-retrofit of your home, consider installing a mechanical ventilation with heat recovery (MVHR) system that maintain constant humidity levels in your home.

Will increasing insulation help?

High quality insulation can prevent damp and mould growth. Expert installation of internal wall insulation, with no gaps or holes, is critical in preventing damp problems developing. Any areas where the insulation may come into contact with moisture, such as around pipes or near the bathroom, should be properly sealed to prevent water from penetrating the walls. Botched installation can lead to increased risk of damp problems. Neglecting ventilation is a common mistake to avoid. For instance, an extra layer of loft insulation, may make your home warmer but it can also decrease airflow and trap water vapour in your home which can lead to damp and a black mould problem. So, it’s important not to fit insulation without ventilation, for example air vents in your attic space.

Black mould poses a significant threat to your home and health. Mould patches on cold spots should never be ignored as it will only increase spores in the air, encouraging more mould to grow. A combination of moisture control, ventilation, and property maintenance all have a role to play in tackling this problem.