mould on furniture at bottom

Have you had new double glazing? If so then this could be a build up of condensation as damp normally creeps along walls where as condensation can appear on furniture etc Hope this is helpful Jason

I would suggest the problem is due to no insulation beneath the floor! you have created a cold bridge for cold air beneath the sub-floor void, when warm air within the room comes into contact with cold air it will condense to water droplets. When you have had previously carpet on the floor, this would have acted similar to an insulation covering and not being a solid surface would have allowed air to travel between joints in the floorboards. You have now created an impervious floor covering where air is not able to transfer through; creating a condensation issue. recommendations: Improve insulation beneath the floor and provide air changes and heating within the room. Note: cold air will be created from the windows also, I would suggest curtains if you have blinds.