Plywood Over Existing Floor. If you don't respect this thickness of ply, then you're highly likely to see rises and falls in your new flooring. Install a layer of at least ½ or preferably 5/8 ply over the existing planks. Don't mop the floor, as it can absorb the water and damage the particleboard.
Plywood decking is a great choice as an alternative to regular boards as long as the right plywood is used. If the first is sagging then your problem is the supporting structure. There are two basic ways to go:
Gallery of Plywood Over Existing Floor
First guess the existing plywood is flat but too thin to hold the load you have then probably the supports ore good so yes add another sheet but much heavier than the first. How to add plywood it's best to vacuum the particleboard first to help the glue adhere. Don't mop the floor, as it can absorb the water and damage the particleboard. When laying it over an existing floor, a thinner plywood panel is acceptable;
