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Hollow walls are an effective way of protecting a home from moisture.

The hollow walls: definition

The hollow walls of a house are also called double walls. They consist of several parts:

  • An inner wall (also called bearing wall), made of blocks of clay, concrete blocks, silico-limestone blocks, or a wooden frame.
  • An outer wall which acts as facing, terracotta, concrete or natural stone.
  • The space between these two walls is called coulisse. This can be filled partially or completely with insulation.
  • An anchor hook possibly connects the walls between them.
  • Finally, a coating is applied on the inner wall.

The hollow wall is particularly used in regions of northern Europe prone to heavy rainfall, because it is very tight. Indeed, the outer wall forms a barrier against rainwater. Depending on the material in which the wall is made, it can either absorb rainwater or allow it to flow along the wall. In all cases, the water does not reach the inner layer, and the building is therefore protected from moisture.

The insulation of a hollow wall

The hollow walls can be isolated in different ways. The insulation is put in place at the slide. This can be:

  • Partially filledThe insulating material is placed in the slide against the inner wall. A gap of 3 cm is then left between this insulating material and the outer wall.
  • Fully completed: an insulating material completely fills the slide.
  • Left emptyIn this case, it is possible to modulate the ventilation of the air layer.

Most of the time, the insulation used is a mineral wool. Contrary to popular belief, it does not absorb water, even when the slide of the hollow wall is filled with insulating material. Mineral wools are treated to be water repellent: they prevent the spread of rainwater in the building.


Video Instruction: How to use hollow wall anchors