Sub Floor Ventilation – How To Get A Damp-Free Sub Floor Area

The right sub floor ventilation goes a long way in ensuring that the indoor air you breathe is fresh and free from pollutants. At Mouldbuster, we make every effort to ensure that our customers get the most effective sub floor ventilation solutions. The purpose of sub floor ventilation is to get rid of the stale moist air found in the under floor and replace it with fresh drier air from outside.

Many building inspectors, engineers and pest controllers recommend subfloor ventilation. The challenge is to install a system that moves sufficient air, is quiet, economic to run and will provide many years of trouble free operation. Importantly, any electrical work must be done by licensed professionals. Many people think they have a damp subfloor, but on inspection, the dampness problem lies elsewhere.

A Typical Solution

A timer controlled, mechanical ducted subfloor ventilation system will provide air flow and air exchange to remove that damp layer of air and keep your subfloor dry.  We need to consider geography (slope), geology (sandstone, clay) and also existing drainage in developing a solution. The best approach is to install the system during construction.


A quality system for an averaged sized home should be around $2500 supplied, installed, including GST and 5 years warranty.


Sure.  Talk to us about supplying a kit.

Why not call and book your no obligation, FREE home assessment NOW!
Please call us today on 0424 042 180 for the best ventilation solutions.

There are different types of ventilation systems that can be installed in your sub floor:

Balanced Pressure

A ventilation system that uses balanced pressure uses two fans. One is a positive pressure fan that brings in drier air from the outside into the sub floor through vents. The other, a negative pressure fan, expels an equal volume of stale damp air from the sub floor to the outside. Balanced pressure is created because the rate at which air is forced into the sub floor is the same as rate with which stale air is forced out.

The balanced pressure system is beneficial in several ways:

  • It is effective in that moist air is pulled from damp surfaces and dry air blows over these damp surfaces to keep them moisture-free.
  • Stale odors and moisture are effectively managed because you can decide the location from which the damp air will be expelled.
  • The system can effectively cover your entire sub floor area since the fresh dry air flows in from one end while the damp air is sucked out from the far end.

Supply System

Your sub floor can have a ventilation system installed that uses positive pressure. This simply means that the amount of air that flows into the sub floor is greater than the air forced out. For this setup, the positive pressure system makes use of two supply fans and one exhaust fan. When fresh dry air is forced in at a higher rate than damp air is expelled, positive pressure is created in the sub floor. This pressure forces out the damp air to the outside. The benefits of this method include:

  • Any damp areas in your sub floor can be dried much faster when the dry air is blown over them rather than pulling the moist air from them.
  • Stale odors and moisture in the sub floor can be managed effectively. However, you need to make sure that the damp air can freely escape to the outside. If a sufficient escape route is not in place, the moisture could end up rising up into the home.

Types Of Sub Floor Ventilation

Exhaust System

In an exhaust system, the amount of air blown into the sub floor is less than the amount of stale air pulled out. This is achieved by using one supply fan and two exhaust fans.

As the moist air is pulled out of the sub floor constantly, a negative pressure is created in the sub floor, which causes the drier outside air to rush in. Stale odors and moisture can be managed well since the ventilation expert gets to select the best location through which the damp air is extracted.

Sizes Of Fans

The size of fan that will be used in your sub floor will depend on the sub floor size and materials used to build your home. The fans can either have an AC or EC motor. AC motors have one speed and are not noisy when in operation. On the other hand, EC motors have adjustable speed and are more efficient and quieter than AC fans. We usually recommend that the sub floor have at least five air changes per hour.

It is best to run the fans during the day when the air outside is driest in order to get the most effective results. Any noise coming from the ventilation system is also drowned out easily during the day.

When you first begin to use the sub floor ventilation system, you may need to run it for up to twelve hours a day in order to keep the sub floor dry. With time, you can begin to reduce the number of hours the system runs. Running the system for a minimum of four hours per day can be effective in keeping your sub floor fresh and dry. You can use a fan with a timer to pre-set the number of hours you want the system to run.

All the components we use for your sub floor ventilation are of the best quality. They are durable and are designed for constant use. The ventilation experts at Mouldbuster are available to assess your sub floor and recommend the best sub floor ventilation solution.

Please call us today on 0424 042 180 for the best sub floor ventilation solutions.