Glass wool insulation of the crawl space

Ventilating the crawl space: our advice

The crawl space is a space between the floor of a house and the ground where it is built. Its main purpose is to protect your house from rising damp. It also contributes to insulation by limiting heat exchange between the house and the ground.

Measuring between 20 cm and 1.80 m in height, this space, whether accessible or not, must be equipped with ventilation in order to avoid an accumulation of humidity in the base of the house. Ventilation of the crawl space is essential, as it prevents moisture from rising and thus weakening the structure of the building.

Why is it necessary to ventilate the crawl space?

In addition to protecting your home's floor from moisture-related problems (standing water, mould, weakened structure, etc.), crawl space ventilation is an excellent way to protect homeowners from radon gas contamination.

Naturally radioactive, this odourless and colourless gas tends to accumulate in confined spaces before rising through cracks and seals in your home. It is recognised as the second most common cause of lung cancer in France, behind tobacco but ahead of asbestos.

How to ventilate the crawl space?

There are several solutions if you wish to limit the health risks inherent in poor ventilation of the crawl space. Depending on the area to be ventilated, you can opt for natural ventilation or a VMC. It is also possible to install a dehumidifier in this space if it is subject to significant humidity problems.

Natural ventilation

Installing natural ventilation is probably the most practical and least expensive solution. By installing screened enclosures (or any other ventilation grille), you will allow air to circulate freely in your crawl space. The resulting airflow will allow moisture and radon gas to escape through the vents.

Daniel Marcellin | Installing ventilation in a crawl space

Controlled mechanical ventilation

Controlled Mechanical Ventilation (CMV) can be useful if there is insufficient ventilation in the crawl space. By connecting a VMC to your cellar and to the basements of your house, you will allow stale air to be expelled to the outside, eliminating the risks associated with the accumulation of humidity (stagnant water, mould) or radon gas.


If your crawl space is so damp that you cannot dry it out, we recommend installing a cellar dehumidifier. Although costly to install, this is by far the most effective solution for removing problems associated with excess moisture. You can also call in a professional if you have a lot of moisture: this is by far the best solution if you want to solve your moisture problems.