Underfloor Fans

If its an older house if often has a fireplace and chimney. If so these are a great way to vent the sub floor in older homes. Cut down in fireplace to sub floor. Install fan. Then cover it up again so its aesthetically pleasing from the inside.

PS: Make sure the the chimney cap is waterproof.

 

I actually ended up installing some sub floor insulation (Green Stuf).
Miscalculated on my order and got a bit too much.

But spending the entire day under the subfloor, I've realised its not as wet as i initially thought it was, it is rather dry on the surface level.

The insulation itself has helped a fair bit. LIttle painful to do though with about 30-40 cm clearance.

 

neK, if your sub floor gets wet - the insulation will get damp and in turn wherever there is an air gap - you will get humidity and in turn this will travel back into the flooring and internals. It is essential you deal with the problem - which is air and high humidity. Resolve the existing fans, by fixing the system design if they were incorrectly installed. Never use positive pressure on its own in the sub floor as you could push the toxic air into the cavity and back into the breathing air internally. Causing sickness. If pushing air in, always balance it with negative pressure of equal or greater flow.. Also never put an inlet vent near where your duct extracts -pointless exercise. Always allow the intake air to travel across your floor before extraction...