Why Passive Ventilation May Not Be Enough to Prevent Mould

Reducing the amount of condensation in your home is important in preventing damp and mould from developing.  Good ventilation means improving the air flow in your property which means that humid air is removed from the environment more quickly, so it does not have the opportunity to settle and release moisture onto cold surfaces.

If you do not have some form of active ventilation in your home such as an extractor fan or whole house system such as Positive Input Ventilation (PIV), you will rely on the natural movement of air through the building to prevent condensation.  Passive ventilation uses windows, doors, and air bricks throughout the house to allow air in and out.

Does Passive Ventilation have any Advantages?

The advantage of passive ventilation is that it is effectively free.  You don’t have to pay for anything to be installed or spend any money on energy to power a fan.  You simply open a window to let in fresh air and allow humid or stale air to escape from the building.

In a house that has been carefully designed to promote natural airflow in a very controlled way, passive ventilation can be highly effective in moving air from one part of the building to another, however very few houses are designed around this principle, and while there may be some benefits, it is very unlikely that a passively ventilated house could move the quantities of air needed to prevent condensation from forming.

Why Active Ventilation Reduces Condensation

The main sources of condensation in a home are the bathroom and kitchen.  Bathing and cooking release a lot of water vapour into the room itself.  If the moisture laden air is allowed to escape into the rest of the house, it will deposit water in the form of condensation on any cool surfaces it comes into contact with.

Building Regulations specify certain levels of airflow from intermittent extractor fans depending on where they are placed in a home.  This is measured in litres / second as follows:

• Kitchen (adjacent to the hob) 30 L/S
• Kitchen (elsewhere) 60 L/S
• Bathroom 15 L/S
• Utility Room 30 L/S
• Sanitary Accommodation 6 L/S

In most cases, an extractor fan will provide a higher level of airflow than is specified, but even the minimum levels are far higher than you could achieve by simply opening a window.

Extractor fans are extremely effective in reducing condensation in your home because they remove the moist air from the source rather than allowing it to spread elsewhere.  If you simply open a kitchen window, the inward airflow into a bathroom or kitchen might do more harm than good, because the wind coming in through the window will push the humid air deeper into your home.

Passive ventilation could make condensation worse in other rooms of you home, and in time this will lead to damp and eventually create the perfect environment for mould to grow.  If you do have condensation problems in your home, or damp and mould patches on walls and ceilings, it is a clear signal that your internal ventilation is insufficient, and as such, you should take steps to address it.

We Can Help You Prevent Mould

The sight of patches of mould growing on walls or ceilings can be worrying, but thankfully improving the ventilation in your home to reduce condensation levels will deal with the problem for good.  If you have found patches of mould growing in your home, contact us today to book a free home survey.  Our local ventilation specialists can visit you and identify the causes of condensation, damp, and mould, and provide you with advice about the best way of removing the problem.  Contact us today to find out more.

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