Mould and decay spores surround us in their thousands at all times. Bacteria surround us in their billions. These microbes actually play a very important function in the environment by acting as garbage men. Without them, the world would be a very messy place. Trees and plants that died would fall over and stay there. Animals that died would fall where they lay (if uneaten by other animals) for thousands of years until erosion processes removed them. Fungi and bacteria therefore are vital elements in the ecosystem. Along with insects, they recycle all living things on the planet and generally keep things looking neat and tidy.
If you are in good health, you will supply one trillion bacteria with food from the flakes of skin and oils you shed every day. They then supply you with body odour. There are trillions more bacteria inside your stomach, nose, eyes and ears, not to mention those that force us to the dentist every six months. Your digestive system alone is host to more than a 100 trillion microbes. We could not survive without bacteria. They process our wastes, synthesise vitamins, convert the things we eat into useful energy and battle unwanted microbes that invade us daily.
Bacteria reproduce fast and are survival experts. The organism that causes gangrene can reproduce every nine minutes. At this rate, a single bacterium can reproduce 280,000 billion individuals in a single day. They can live and thrive in just about every environment we can imagine providing they have one thing – moisture. They can consume just about anything. There are bacteria that live in highly concentrated sulphuric acid. Others that live and consume the waste from nuclear reactors, some in boiling mud pots and others in lakes of caustic soda. They have been found 11 kilometres deep in the ocean. A Streptococcus bacterium was recovered from the sealed lens of a camera that had stood on the moon for two years. We find them just about everywhere we can imagine, in the most extreme conditions. When conditions start to get tough, they simply shut down and wait for things to improve. Scientists have reactivated Anthrax spores thought to be dormant for 80 years.
Fungi are one of the specific forms of life that do not fall into plant or animal categories. They include mushrooms, moulds, mildews and yeasts. Fungi are closer in structure to animals than they are to plants. Some fungi root, but otherwise they have few plant-like qualities. Their cells are made from chitin, the same substance used to make the shells of insects. Fungi also do not photosynthesise, an essential process for all green plant life.
The common link between decay fungi, mould fungi and bacteria is that they all require moisture. Managing these organisms means we have to manage the one essential factor they all need for survival – moisture. Remove moisture from their environment, and they cannot reproduce.
For home owners, mould and decay fungi are bad news. Moulds such as Penicillium, Aspergillus and Stachybotrys along with gram negative bacteria pose serious health risks to those who are constantly exposed. Decay fungi reduces the strength of structural framing members increasing the likelihood of catastrophic failure of building components resulting in injury or death.
Decay fungi are managed to a certain extent with timber treatments. However, if there is excessive moisture, timber treatments merely delay the inevitable fungal decay victory. Stachybotrys, Aspergillus and Penicillium are moulds that particularly find leaky buildings attractive to live in and reproduce. Gram negative bacteria can be found in the warm moist environment of wet carpet.
Stachybotrys itself is not pathogenic, but it can produce chemicals such as T2 and satratoxins, F, G and H, all Trichothecene Mycotoxins which are extremely toxic, carcinogenic and immunosuppressive. Penicillium allergies affect a minority but nevertheless can be a huge source of discomfort to those affected. The allergic response is not generally pleasant, particularly when the occupant has no knowledge of the source. Allergic Broncho-pulmonary Aspergillosis (ABPA) can affect individuals with asthma or cystic fibrosis. This is thought to result from Aspergillus Fumigatus growing in the lung and sinus tissues. This is but one of the many illnesses caused by Aspergillus.
Gram negative bacteria are a group of bacteria classified by their cell wall construction, in particular Lipopolysaccharide (LPS) which triggers an immune response as it acts as an endotoxin. There is also some evidence that exposure to non-toxic fungal spore cell wall components known as (1″3)-b-D-glucans), which are simply fungal spore “parts” cause inflammation of the respiratory system, particularly in infants and the elderly.
When we look at a leaky home in regards to repair and the actions we need to take, there are two major considerations – Cause and Effect. Cause is fairly obvious, whatever leaked – fix it. Sometimes however, the only way to find cause is to see the effect. Aside from water damage to linings, this is usually in the form of decayed or mouldy construction materials. If we have either of these two scenarios (decay or mould) within a particular wall cavity, the usual solution is to provide a dry environment via installation of a drained and vented cavity.
The amount of moisture required for decay and mould fungi and bacteria to establish themselves isusually considerably higher than the amount of moisture required to keep them growing. For example, Stachybotrys requires a 90% relative humidity to initiate but if moisture levels drop, it can keep growing down to a relative humidity of around 70%. Moisture and humidity levels in houses, especially leaky ones, vary with changing seasons. Once these micro organisms are established, the moisture levels required for them to continue to grow are much lower. In terms of remediation, this places significant emphasis on keeping construction materials dry.
Construction workers in the remediation industry must be trained in regard to the hazards that they face from these potentially harmful microbes. Gloves, dust masks, even Tyvek suits are required to protect them from poisons, carcinogens and potentially harmful microbial growth in their lungs. If we consider that the risk to remedial construction workers is high, then the health risk to residents who are exposed daily on a long term basis may be even higher. The consequences of this for remedial design means that decayed framing or potentially decayed framing is not the only safety consideration that will tip the repair from targeted to full re-clad. The growth of mould and bacteria must be considered just as important.
A hypothetical example; we have a leaking house built five years ago with H3.2 CCA treated framing and a directly fixed monolithic cladding. The traditional view by many would be that the chance of long term structural damage is low and therefore targeted repair only is required. Let us now put aside the fact that even small amounts of moisture can cause decay to H3 framing given the 50 year minimum timeframe required by the Building Code. Let us assume we will have no structural issues over the next 50 years. We have small amounts of leakage occurring at joinery, and destructive investigation reveals Stachybotrys on plasterboard linings. What do we do? Risk is determined by the chance of something happening multiplied by its consequence. We now know that target repairs have a reasonably high chance of failing. The consequence of the failure however, is the potential for residents to be living in a toxic environment. The “risk” is unacceptable.
The target repair option must be excluded on the basis of the risk of future leaking into the wall cavity, continued growth of the microbes and potentially devastating effects on the health of the occupants. It is a no-brainer. Harmful mould spores spread throughout a house requires a re-clad.
Mould, decay and bacteria need moisture. Provide a dry environment to the exterior envelope and reduce the health risk to occupants.