What causes soft floors

I am sure some manufactures use CDX or OSB3,4 plywood but the floor I had to fix in our 2016 Sand Sport was neither of those. I suspect it was OSB 1or 2 both of which are not water resistant. There is nothing wrong with OSB category 3 or 4 in wet locations.


If you feel a soft spot in the floor the plywood has rotten from repeated water intrusion.

Our camper has a sandwich floor and there is a tunnel in it for wiring to go to the other side from the load center. It definitely deflects when stepped on but hasn’t gotten worse over the years.
You may be seeing the same thing in some of the units you have looked at.

There is what feels like a "soft spot" in the floor of my trailer. It is the only spot in the floor that flexes slightly as I step on it. It is an unsupported seam where 2 pieces of 3/4" plywood flooring come together.

The seam crosses over the heat duct which runs down the center of the trailer. The duct is stapled directly to the underside of plywood flooring. It does make the center isle warm for the feet when getting up in the morning or getting up to go to the bathroom at the back of the trailer when winter camping.

Bad design and use of interior low cost material.

Some RV floors have a sandwich type of construction where foam is in the center. That type can weaken with use till there is a total failure.

Others use a plywood or OSB material that will fail if it gets wet.

The repair for each type is complete replacement of the affected area. Search for videos that will help you with the project.

Could be the construction method too. I've seen the floor have a sheet of Styrofoam between 2 sheets of plywood. Hallway was spongy

Yep. Dryrot. Usually found under sinks, in front of shower/toilets, and sometimes a window or vent left open. Very seldom does it happen from below.