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  • Writer's pictureCliff L'Aimable _Chartered Surveyor & Building Engineer

Black Mould the danger to building occupants

Updated: Dec 3, 2022

My company and team offers private Building Regulation Approvals, technical design, reports and plan checking, site inspections of all building projects. Tel 01992 710 763 EmaIL

A blog post by Cliff L'Aimable Chartered Building Control specialist -

Finding mould in your home can invoke reactions of distress, especially when it has spread in a concealed location, and is present in rooms occupied by young and elderly family members.

Black mould Stachybotrys chartarum Building Control Advice
Black mould health risk to occupants of buildings

(Photo) Black mould discovered when a wardrobe was moved away from a bedroom wall

The presence of fungus.

Moulds are a fungus that presents itself in varying colours, but in buildings the unsightly rounded black and greenish patches on plastered walls, on timber skirtings, and around window frames is what occupiers observe, and which must not be ignored when discovered. Areas affected should be immediately treated to prevent further spread.

So what distinguishes fungi from funguses? The word "fungus" is pluralised as "fungi." Fungus often refers to a single species when used as a term.

So what is this invasive attack ?

Mould is a particular kind of fungus. It develops as hyphae, which are multicellular threads. Yeasts, on the other hand, are fungi that have the ability to adopt a single-celled growth habit.

Establishing context to risk to humans

There are millions of fungal species, of which approx. 300 are capable of causing disease in humans. They flourish on plants, in soil, and in water, often being difficult to see with the human eye. There are fungi floating and settling down everywhere around our built and open environments.

Fungi can also settle and embed itself into our skins, even inside our bodies, but putting this into some context only a small number of the millions of fungal species that exist have the ability to harm humans, as I have already mentioned.

Black mould health risk in context
Mould_Fungi in the general environment

Conditions promoting fungal growth are typically found in damp, dark corners of building interiors, where air movement maybe lacking. Initially looking harmless, it can develop into a significant health concern to building occupants exposed to the mould, which potentially longterm can damage structural building components such as timber and of course decorative finishes and objects in close proximity to its occurrence.

Stachybotrys chartarum is typically associated to the general term of reference "black mould" – in reality it has a blackish green appearance, rounded yet irregular specular shapes, which when viewed very close up can have micro fibrous strands which eventually will emit dangerous spores into the air, causing building occupants to suffer from life changing respiratory issues, including asthmatic conditions etc.

Mould is fungus in its mature stage, whereas "mustiness" is fungus in its early stage.

Since mould has a propensity to spread continually under the right conditions, it progressively contaminates other objects and surfaces, giving off a distinct odour and polluting the air during its life cycle.

Other prevalent moulds include the seemingly exotically named Alternaria, Aureobasidium, Chaetomium -fungi.

Moulds produce allergens, irritants and potentially toxic substances or chemicals called (Mycotoxins). Significant neurological, cognitive, or hormonal symptoms are frequently present in true mycotoxin-induced disease in humans. Even though mould allergy can be severe, it typically manifests as tiredness, seasonal allergies, and respiratory problems most commonly.

Dry rot Serpula lacrymans_ Building Control Surveyors

Dry rot fungus attacking and consuming floor and skirting boards

Two wood-eating fungus known as dry rot (Serpula lacrymans) and wet rot ( Coniophora puteana--Basidiomycetes)

Are also commonly found in and around buildings. Especially if the building has not been routinely maintained. These fungal types are not known to affect humans.

Black mould
Mould around window

Fungi flourish on damp, cellulose-rich surfaces including fiberboards, wood, drywall construction which includes plasterboard, where it can proliferate and release spores into the air. Mould may also grow in areas subjected to minor leaks and infiltrating moisture..

Is Black Mould Toxic ?

Black mould is toxic, since it releases substances known as mycotoxins that can be quite dangerous to occupants of buildings . Inevitably some individuals are more susceptible to the effects of inhaling fungal spores than others and may experience respiratory conditions as a result.

Depending on the quantity of mycotoxins present, the length of time exposed to them, and other variables, an environment with a high concentration of mycotoxins can eventually lead to fungal poisoning to occupants sleeping and generally living in habitable spaces where ventilation in particular may be poor.

Exposure to fungus is particularly dangerous for young children and infants.

Children who are exposed to mould may be more likely to develop asthma, according to established research. The World Health Organization published a report in 2009 entitled "WHO Guidelines for Indoor Air Quality: Dampness and Mould" (WHO Report) which documented an extensive evaluation of the research journals covering health issues related to biological agents and moisture in buildings which included the effects on building occupants.

The investigative information contained in the WHO Report came to the conclusion that, in addition to immune system suppression, the most striking outcome of mould being present in occupied buildings is the correlation in the increased prevalence of respiratory health problems, allergies, and asthma in humans exposed to fungi such as black mould.

Prevention of Black Mould

Preventing (or minimising) prolonged dampness, excessive humidity levels and conditions allowing microbial growth on interior surfaces, and generally within building structures are the most crucial steps in helping to avoid detrimental health impacts upon human inhabitants.

Design of new buildings or upgrading existing buildings

Those involved in the design of buildings that maintains the health of the occupants over a buildings lifespan is certainly a key desirable -aesthetics apart.

New buildings should be designed to incorporate a select package of design features tailored to suit the development by :

1. Minimising heat loss by provision of floor, wall, ceiling, roof insulation as part of an air tight arrangement.

2. Control excessive heat gains.

3. Incorporate suitable controllable ventilation provisions using low energy forced mechanical extract fans in kitchens and bathrooms were appropriate – that extract high moisture ladened air straight out of the building – as part of an air-tight building.

4. Provide thermal breaks and avoiding “cold bridges” in the built construction.

5. Provision of user adjustable fixed background ventilation (basic air brick ventilation, trickle vents on windows or if the budget permits using Mechanical Ventilation with Heat Recovery (MVHR) which is a continuous source of ventilation that extracts stale, moisture-laden air from a building and resupplies fresh, filtered air back in with heat recovery, resulting in a comfortable and condensation free environment all year round.

A combination of the above to suit the building proposal would help to significantly reduce health threats from mould within your home. Your building control professional should be able to assess compliance with building regulations in that capacity.

Existing buildings reducing mould

Nevertheless, despite how challenging it is to stop the growth of these dangerous microbes in structures, there are several safeguards that can be taken:

• Conduct regular inspections to identify and fix any minor cracks, roof components, and waterproofing that might cause a leak.

Monitoring and maintaining a humidity level of between 40-50% ideally.

• Ensure that there is little dampness within the house.

When possible, let the sun and air enter the building naturally.

It is crucial to clear the area of mould if you still see it there .

It is advisable to hire experts if the issue is significant. However, there are a number of homemade solutions easily available on the internet that typically include bleach sprayed mixtures which ought to be effective when treating minor breakouts - These although only offer temporary fixes.

Otherwise building occupants must adequately ventilate their homes particularly if cooking food, bathing, or drying clothes , whilst balancing the regularity of heating homes.

You must always try to identify the reasons why mould growth is developing in your home and eliminate that cause. email or telephone 01992 710 763.


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