Moisture problems in the crawl space

Many homes only have a crawl space. Here too, of course, moisture problems can occur due to the flooding of the crawl space (due to the infiltration of groundwater) or due to rising damp from the groundwater.

The high humidity that often prevails in crawl spaces creates a large difference in vapour pressure between the crawl space and the living area. In this way, moisture can enter the house via an open connection. Open connections can be, among other things:

  1. Shutters in the crawl space
  2. Meter boxes with pipe penetrations
  3. Connections between floors and walls

From the crawl space to the living area

Many cellars and crawl spaces are sometimes flooded or have high humidity. This humid air can find its way to the dry living area in three different ways:

  1. Vapour diffusion: water vapour goes from zones with a high concentration of vapour (where there is a high vapour pressure) to zones with a lower concentration of water vapour.
  2. Capillary moisture transport: capillary pores are continuous, interconnected pores in, for example, cement stone with a size between approximately 10 and 1000 nm. In construction, capillary action occurs when water is sucked up by bricks (rising damp, rising damp).
  3. Air transport: an air flow from the crawl space to the house can occur if the crawl space has an open connection with the outside air, if there are air leaks between the crawl space and the house or if there is a large pressure difference between the crawl space and the house.

Solutions for a dry crawl cellar

1. A damp crawler cellar should first and foremost be fitted with good ventilation grids so that condensation in the room does not get a chance.

2. Air leaks between the crawl space and the house must also be closed if moisture problems occur. These air leaks exist for various reasons:

  • Piping from the basement to the house
  • Crawl space shutters or cellar shutters
  • The capillary action of the house floor itself

3. Pressure differences between the basement area and the house need to be addressed. Differences in vapour pressure can be caused by three factors: the 'chimney effect' in winter (due to the temperature difference between inside and outside), a mechanical extraction that is not properly adjusted or the wind pressure that creates suppression and overpressure.

The basis is always: air flowing in through the underpressure must somehow be able to flow back out again. If the differential pressure cannot recover naturally, it must be balanced manually with the installation of, for example, a ventilation system.

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