Monday, September 25, 2023


Ask Dave: Thor says my soft floor is normal, but it can’t be!

Dear Dave,
I have a 2017 Thor Synergy that we LOVE, but a year after the dealership delivered it, the floor in the living area started going soft. The unit was bought new. Repeated calls to Thor warranty assured that this was normal. No evidence of water damage. We live and travel in a very dry climate. We have lived with this for five years. Can the floor structure be replaced? —Bob, 2017 Thor Synergy

Dear Bob,
I do not believe that a soft floor is a “normal” situation. I think the block foam insulation is breaking down in a heavy traffic area. Most manufacturers use a sandwich design for the walls and floors that were actually patented by Winnebago Industries in the late 1960s or early 1970s called Thermo-Panel. It was a one-piece aluminum outer skin, luan paneling, block foam insulation, and another luan panel all laminated together and run through a pinch roller. It was such a strong design it did not need framework inside the panels.

The aluminum was replaced by fiberglass and companies used this design for floors and roofs. From what I can find in researching the design of your floor is that Thor used luan plywood on the bottom, 2” block foam insulation, and a slightly thicker upper deck before the final floor covering, which is probably vinyl. This floor sits on a metal framework that is welded to the Mercedes Class C chassis to give it support. However, the framework is not 16” or even 24” in the center, like most houses. Sometimes the span can be as much as 50” or more, and oftentimes we see the heavy traffic areas start to get soft.

The biggest problem area that I have seen is where the traffic area is sitting above the catalytic converter or muffler. The extreme heat adds to the breakdown of the block foam. The situation gets worse the more you let the unit sit and idle, as there is no airflow like when you are traveling and the heat intensifies.

Couple of fixes for soft flooring

There are a couple of fixes depending on the severity of it and the access underneath. Sometimes you can go underneath in a compartment and weld cross members in the area to help support it or even use a 2×4 vertically with a piece of 3/4” plywood horizontally. But it cuts down on storage and looks a little DIY.

What we have done in the situation where the block foam actually shrinks due to the heat is peel back the flooring material, cut the plywood deck, and cut out the soft block foam. We replace it with 2x4s shaped like a ladder—two going lengthwise and shorter cross members. We then fill the spaces with blue block foam, which seems to hold up better.

It must be “soft floor month,” as I’ve gotten this question about four times now! Another option is to do what our reader Richard did and install a 3/4” marine grade plywood cutout over the entire soft area.

 You might also enjoy this from Dave 

Ask Dave: My RV’s flooring is soft. Can I remove the top boards to replace?

Dear Dave,
I have a soft spot on the floor near the kitchen and entryway. I was told by a reliable repair shop that the floor is a sandwich of thin plywood and Styrofoam and that there is no structure underneath (unlike a porch) where you can remove the top boards and replace what holds those boards up. Is that true? I am of a mind to place 3/8″ plywood over the whole area to cover the soft spot since it seems like there is plenty of solid floor around the edges of the soft spot. I love this trailer—everything works in it and I do not want to go out and buy a new one. Any thoughts on why my RV’s flooring is soft and how I can replace it? —Richard, 2015 248RKS Bullet

Read Dave’s response.

Dave Solberg is a leading expert in the RV industry and the author of the “RV Handbook.”

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Dave Solberg
Dave Solberg
Dave Solberg is a leading expert in the RV industry and author of the “RV Handbook” as well as the Managing Editor of the RV Repair Club. He has been in the RV Industry since 1983 and conducts over 15 seminars at RV shows throughout the country.


  1. I think I’ll keep my 92 Jamboree. It has low mileage, no leaks and solid floors. Plus, it has minimal electronics and is very reliable.

  2. Everytime I read about intentional “cheap” build processes like this I am SO glad I have a Newmar. They still build the underlying structures like a fine home. No soft floors…no delamination risk.

    I have been in brand new rv’s at shows with these under supported floors and they feel like sponges even when new! I guess a lot of buyers are paying too much attention to blue lights and other “glitter” to notice that the build construction is inferior.

  3. Dave, that was a very interesting article about soft flooring. Especially the part where your the catalytic converter or muffler are below the soft areas. especially if you’re not traveling along with air circulating! I bet there are a few, maybe more RVers that are thinking, hey we sometimes run our engines while camping to charge our batteries. I bet if they have read your informative article they may reconsider running their engine. Perhaps having a diesel in the back won’t be the same issue. Actually it did sound like Bob should have pushed harder to get that soft spot taken care of while still under warranty!


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