Subfloor Ventilation in Melbourne

Subfloor Ventilation is the key to a healthy subfloor and therefore a healthy house.

In brick houses and especially older brick houses, there is typically too little natural subfloor ventilation in the crawlspace. When coupled with the older brick or bluestone footings - which decree that each room in the dwelling is mirrored with the same chamber in the void beneath the house - there is both no natural ventilation of this crawlspace area and no cross flow ventilation. In these instances the only way of improving crawlspace ventilation is to install mechanical subfloor ventilation.

Symptoms of a poorly ventilated subfloor

Generally speaking, people will notice when they have a poorly ventilated subfloor (and therefore a damp crawlspace) by the presence of a damp, mildew or musty odour. Further investigation may reveal the presence of fungal growth on both the soil and any brick footings. In more extreme cases evidence of rising damp, brick and mortar deterioration is very common.

Once the symptoms are apparent, then mechanical subfloor ventilation of the crawlspace is generally required.

Subfloor Ventilation Procedure

Once it has been determined that the subfloor requires ventilation (by the presence of long term moisture, fungal growth, rising damp deterioration to brick foundations, etc.) the process for installing a subfloor ventilation system is as follows.

1. Moisture tests

We initially conduct a moisture test of the subfloor atmosphere and the subfloor soil directly from the crawlspace. If we are drying the subfloor before installing fans we do before and after soil and atmosphere tests so we have something to measure the success of the ventilation from.

2. Measure subfloor area to be ventilated and determine access

Obviously access to the crawlspace and the structure of the crawlspace is important.

• i) Access to the subfloor or crawlspace - The best types of ventilation systems are those that are ducted to all corners of the crawlspace or into every cavity (if the property is solid brick where each internal room is mirrored by a subfloor 'room' or chamber). If the access is sufficient to enable a ducted system to be installed, then the next step is to measure the area to be ventilated.
  (If no access - If there is no access to the subfloor then the only option is to install fans mounted in the external wall of the dwelling. These, although better than nothing, are not nearly as efficient as the ducted system because they lack the power to draw air from other room cavities in the subfloor. The reason they are not powerful enough is that the restriction of the physical size of the fan and housing (typically one or two brick sizes) also restricts their output).
• ii) Area - The science of installing a subfloor ventilation system is a mathematical equation which is simply the cubic meterage of the crawlspace (width x length x height of crawlspace) divided by the output of the ventilation fans to be used. Our aim is to achieve 8 air-changes per hour of operation of the ventilation system, as per the relevant Standards that govern home ventilation. Therefore, assuming an area of 100m3, the required output of the fans to achieve 600m3 (100m3 x 6 air-changes per hour of operation) would be 600m3. For air to be introduced to the subfloor, we allow 3 air-changes per hour. There is more to it than that as the ducting added to the fans reduces the fan performance but that is the general idea.

3. Select the best and quietest fans

There are a lot of different fans on the market. One of our competitors calls them air pumps but they are in fact fans. Our ventilation fans are sourced locally but manufactured in Europe, have a five year warranty and are the quietest fans on the market  (Technical specifications for our Quiet Subfloor fans). The decibel output is important, for obvious reasons.

4. Positioning and installing fans and ducting in the crawlspace

Our fans are all mounted on a chipboard base with a 20mm rubber barrier installed between the fan and the particle board base. They are then either screwed onto the joists or mounted on the floor of the void. The ducting is run to every cavity in the subfloor and the fans are balanced in the subfloor (subject to access) so that they are evenly distributed to allow an even spread of air throughout the subfloor.

5. Switching

The fans are installed with either a 24 hour waterproof timer (pre set to run during daylight hours for a set period of time and adjustable) or via an hygrometer which turns itself on and off depending on humidity levels. The fans are generally set to run when occupants are not there and the times they run can be adjusted to suit.

6. Inspect and re-adjust

As part of our service, we will return to the property on a set date and check the moisture content of the crawlspace and internal flooring and walls. Once we have established all moisture readings we will reset the timer up or down depending on the results we have achieved in the first month.