Eighteen months ago we filled in a sunken den on a slab floor with a wooden decking, then covered with laminate flooring. a couple months ago, we noticed soft spots. When we pulled the floor up, all the wood was rotten! No evidence of standing water, don't think there was an kind of leak. Could the fact that the floor had no kind of air flow cause condensation to build up and rot the wood? Help! We live in south Louisiana.