Sub-floor ventilation fans are very effective for removing mould, damp smells and drying excessively damp earth below your building, but there are a few things you should know before installing them.

Installing Sub floor fans sounds like a “great idea” to cure rising damp. After all, the walls are wet so why not just dry them out with fresh air?

If you have rising damp, installing fans will likely accelerate the damage that rising damp causes. Speeding up the evaporation of water from the masonry will deteriorate the bricks and mortar below your floors FASTER, turning them to dust.

WHY?

Because rising damp is just as much about salt as it is about water. 

Let’s define “Rising Damp” by saying what rising damp is NOT. 

• Rising damp is not damp smells. (you can have rising damp with or without damp smells)
• Rising damp is not mould. (You can have mould with or without mould)
• Rising damp is not rotting bearers and joists in your floor.

Rising damp SPECIFICALLY is the capillary action of water containing minerals, through masonry to an evaporation point. 

It is called Rising Damp because as the water rises up the walls to the evaporation point, the water evaporates at the lowest point (path of lease resistance). As the pores of the masonry block with salts the water will go a little bit higher to evaporate more easily. As the pores of the masonry become filled with salt, the water creeps up the wall until gravity prevents it rising any further, then the salts will start to accumulate below the maximum rising damp height which is limited by gravity.