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VENTILATION

Ventilation is critical for the longevity of the building fabric, for health of buildings interior and the health of those occupying buildings.

When considering adequate ventilation, the entire building needs to be assessed and ventilation needs to be designed taking into consideration all sections of the building, it is not adequate just to increase the cross flow ventilation to the sub-floor without taking into account the temperatures and humidity levels of other areas of the building for example. It is easy to recommend additional ventilation and admittedly, any added ventilation is generally beneficial however to get correct ventilation many factors need to be considered.

Many aspects of ventilation and/or lack of, are still misunderstood by the professional and scientific communities, many are sure they have a thorough understanding however as with any natural occurrence, we continue to learn, the more we know the more we realise we do not necessarily know that much.

With the introduction of the likes of thermal imaging and various moisture meters and humidity sensors, we do have a better understanding of where humidity occurs, where condensation occurs and what areas need to be ventilated.

Doing a recent job, I found a unique set of circumstances where vapour was causing significant moisture issues in a building, I was unable to fully establish the source of the moisture until I undertook some experimentation of my own, using the Darcy's law/equation of fluid transfer through porous materials I carried out a multitude of tests that clearly proved beyond reasonable doubt that the vapour transfer from a high vapour pressure area to a low vapour pressure area was the primary source of moisture to various voids within the building. Only by understanding the source of moisture, is it possible to determine effective ventilation.

I have an additional job where I an still currently carrying out trials to determine an effective ventilation system, the walls of the areas with excessive condensation are facing north/west and normal cross flow ventilation will not work as this is the lowest area of the sub-floor, all levels above are affected by differential humidity and temperatures that a reoccurring, an inappropriate ventilation system has actually increased the issues in this instance, I am currently working on an effective alternative.

Every building has numerous voids, some of these voids are totally sealed on all sides, it is not uncommon to find that condensation forms within these enclosed voids inturn promoting fungal growth and often attracting termites, I have been working over a long period of time to better understand and find appropriate measures to ventilate these voids, no one size fits all solution exists and every situation needs to be assessed on an individual basis.

Sub-Floor Ventilation

Many buildings in Australia have suspended flooring with a sub-floor void.

The sub-floor area is often enclosed and poorly ventilated providing an undesirable environment that is conducive to fungi growth, mould growth, termite activity and wood decay.

Correct sub-floor ventilation often reduces the risk of these factors and improves the quality of living within the dwelling.

Incorrect ventilation can cause significant problems including structural issues - therefore one should never consider ventilation to be a silver bullet and any alterations to current ventilation needs to be properly considered, for example: if ventilation is increased over highly reactive clay soils then the moisture content of the clay soils could vary causing heaving of the foundations.

In general terms sub-floor ventilation is divided into two forms, natural cross flow ventilation and mechanical ventilation.

We have expertise in creating the most desirable ventilation for the type of building considering the buildings physical location.

To create good sub-floor ventilation we need to consider the exposure of a particular building to prevailing winds, the overall size of all the openings in relation to the void that needs to be ventilated and that ventilation openings correctly correspond with openings on the far side of the void to be ventilated.

It can also be very important to have correct (or controlled) ventilation at certain times of day or alternatively under certain weather conditions. Many will consider installing mechanical ventilators that work during periods when the weather outside is warm and humid as is often the case in the middle of the day, therefore actually introducing higher humidity into a void and causing poorer conditions within the sub-floor and the interior of the building.

When considering sub-floor ventilation it is important to consider natures physics. Hot air will absorb larger amounts of humidity and tends to rise while cold air will compress and therefore reduce the amount of humidity and stay lower. In realising this simple fact we can design our ventilation to suit particular conditions and use nature to assist in providing us with the most advanced ventilation. This is an area that our expertise on the subject of ventilation has been so successful, in many cases we will adapt the natural forces of nature to provide us with a superior ventilation system.

In recent years I have had trouble understanding one of the most popular sub-floor ventilation systems on the market simply due to the fact that it goes against all physical theory of preferred sub-floor ventilation. The solar fan concept has had me scratching my head over time as to why this system should provide beneficial ventilation. It is powered by solar panels that are charged during daylight hours by the suns rays, therefore it is often working when the conditions are warmer and therefore the ability of the air to absorb moisture is greatest. Sadly, without prejudice to the manufacturers or marketers of these products, I have personally observed on numerous occasions, while inspecting buildings that these systems have in some instances actually contributed to a higher level of humidity under a building rather than the desired affect of reducing the humidity.  Having said this - we still encourage some type of ventilation rather than no ventilation at all.

It is often not enough just to provide ventilation under a building and this is where we have found the concept of Sub-floor Solutions so effective as we also alter the environment under the building together with the installation of additional sub-floor ventilation.

An interesting fact to consider, it is common for me to observe buildings that are built on brick pier foundations with open sides to the sub-floor, therefore having maximum cross flow ventilation at times to the extent that a candle will blow out if lit within the sub-floor but the ground of the sub-floor is moist with significant mould & fungi growth, the interior of the building has a musty smell with higher than normal humidity levels, improved ventilation will not solve the problems within these sub-floors. From this we can readily conclude that increasing ventilation will often only have a limited effect on reducing the humidity within a sub-floor and that additional measures are often needed to improve the sub-floor environment.

Many Building and/or Pest inspection reports recommend increased ventilation regardless to specific site factors - not always is ventilation the desired option and one should be very wary before racing down to the local hardware store to purchase vents to install himself - you may save a few dollars in the short term but cause major structural issues that could cost thousands in the longer term.

The information on this page is generally brief and only explains a very small part of the overall complexities related to correct sub-floor ventilation.

Roof Void Ventilation

Roof void ventilation is very important, the appropriate ventilation of a roof void will release humidity and vapours to the upper atmosphere, it is very important to have a properly ventilated roof void.

Flat or skillion roof designs are particularly difficult to ventilate properly, any roof with sarking to the underside of roof tiles and/or with metal roofing needs to have a rotary extraction fan (whirlybird) at least installed to the upper roof line.

Cavity Wall Ventilation

Wall cavities that are open to the sub-floor and the roof void provide a free flowing connection between the sub-floor void and the roof void assisting in the natural rising of humidity from within the sub-floor into the roof void, however, in a building that has a poorly ventilated roof void this can work in the reverse and causes excessive condensation within the sub-floor.

For further information please contact Stephen Koelewyn


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Last modified: 1 January, 2017

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