How Do Subfloor Systems Work?

Correctly installed sub floor systems help slow the unwanted progress of rising damp or mould. Installing an adequate ventilation system in your underfloor space will reduce the moisture in the air under the home.

Important! Sub floor ventilation will help with the symptoms but you should always fix the root cause, for example improve drainage, fix leaks, fix rising damp etc. Some problems may need a degree of expertise, so contact the relevant qualified trades-person.

The principle behind our sub floor equipment is to create a good cross flow of ventilation through the sub floor. Our sub floor ventilation kits are carefully designed to achieve this for a range of different sized areas. Our systems will effectively remove the excess moisture in the sub floor area using a fan. The fan is designed to pull the moist air from under the floor and extract it to the outside. Our kits come complete with all the ducting and vents to ensure the system efficiency and effectiveness.

But a fan by itself won’t achieve good cross ventilation. You also need enough passive vents strategically positioned along the perimeter of the sub floor area. These ensure fresh air can enter the space. Passive vents are availableĀ here along with all other accessories (duct, timers, etc).

Many houses have the old style terracotta brick vents. The holes in these vents are usually quite small. Over time debris and dirt blocks these vents which prevents the free passage of air. So it’s important to keep vents open and in good working order. Otherwise, no fresh air will be able to enter the sub floor area.

Using the sub floor area for storage may also block air flow. Mounds of earth and walls also cause problems. In spaces like this you need more than passive vents.Use one of our fan assisted systems to move the air.

Using a ducted system, fans can create air movement in places where vents can’t reach e.g. an internal room or a retaining wall.

Example of a Subfloor System

The following diagram is an example of use with our DIY Subfloor Kit 4. You can see where fresh air enters through existing passive vents with the ducting, vents and BTO connecting the inline fan to the external vent.
sub floor kit 4 diagram

A DIY Subfloor Systems For You

Here at Subfloor Fans Warehouse, we stock DIY kits that include the everything you need for a sub floor ventilation system. Most kits include an inline fan, ducting, external and internal vents and in some cases a BTO, timer and flex & plug. For a complete list of any kit’s components, check the product listing. If you need extra parts, see our Subfloor Accessories here.


The information provided is general in nature and is therefore not always in line with your unique situation and requirements. We advise you to seek professional advice as we cannot be responsible for the items you purchase for your project as each situation is different.