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Environmental ventilation


Rising damp, excessive moisture, buckled floor boards, mould, condensation are all symptoms of excessive moisture, often caused by a lack of ventilation.

The presence of moisture in the crawl space does not of itself mean that a permanent mechanical ventilation system is required. If the reason for the moisture is preventable and/or caused by an event which is controllable, then a ventilation system may not be necessary.

If however, the problem is caused by structural issues - a permanent lack of ventilation which can only be overcome by mechanical intervention - then it will be necessary to install a permanent mechanical ventilation system which will stabilise the subfloor atmosphere so that moisture will not enter the living areas and mould will not grow. Subfloors must be ventilated one way or the other to ensure that moisture which is naturally inherent in soil can escape from the subfloor crawlspace. Modern building regulations provide for passive ventilation which provides cross flow ventilation allowing the subfloor moisture to escape. Older houses are the ones which most often have ventilation issues in the subfloor which can lead to rising damp. In this instance, installing mechanical ventilation is often the answer.

Air expelled and air introduced

Our ventilation systems are unique to the industry in so far as we install fans that both input air and expel stale air. This provides a cycle of fresh air in and stale air out, providing the subfloor with the very best ventilation possible. All three (most systems are a minimum of three fans) fans are controlled by the one waterproof timer.

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. 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 area to be ventilated and determine access

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

i) Access - 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 area). 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 6 airchanges 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 airchanges per hour of operation) would be 600m3. For air to be introduced to the subfloor, we allow 3 airchanges 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 fans are sourced locally but manufactured in Europe, have a five year warranty and are the quietest fans on the market (for fan specs, please click here). The decibel output is important, for obvious reasons.

4. Positioning and installing fans and ducting

Our fans are all mounted on a chipboard base with a 20mm rubber barrier installed between the fan base and the floor joists. They are then screwed onto the joists. 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 (preset 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 crawl space 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.