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Full Version: How thick are your inner walls?
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I need to figure out what thickness plywood to use in my build. I don't have a whole lot of experience with plywood construction, especially long-term, and would like to conduct a brief survey of those who have a similar design in their vans/trucks/campers:

1. What type of vehicle?
2. How thick are the floor, walls, and ceiling, and how are they attached?
3. Are you happy with them, or if you could change them to be thicker or thinner, would you?

I calculated that using 1/2" plywood all the way around in my step van would cost about $320 and weigh about 280kg (about 620lb). I'd like to use thinner sheets, but am afraid of sagging, as well as being too weak to support hooks, shelves, and the like. My design calls for the interior plywood to basically float inside a layer of insulation, braced only against itself and not attached to the outer walls at all.
when I used to do van conversions(age of dinosaurs). we used 3/4 inch for the floor and 1/8 for the walls and ceiling. but we attached it to the ribs. you have to, to fit the contours. it's very important to use real plywood if you want to contour it and not that fake stuff. if you don't attach it how are you planning to contour it? highdesertranger
All of the various wall panels themselves are 1/4" plywood or Luann panelling covered with CCF and vinyl.

But they are attached to the van itself by screwing them in to 1x3's running horizontally across the ribs. I also used 1/3's and my kreg screws to flush mount vertical boards between the horizontal ones where I needed to connect two panels.

The ribs in the GMC are contoured with multiple cut outs in them which made them impossible to fasten panels where I needed to, hence the use of the 1x3's.

IMO, "My design calls for the interior plywood to basically float inside a layer of insulation, braced only against itself and not attached to the outer walls at all." is likely to result in an unstable wall that will rattle like crazy going down the highway. You need to have everything securely fastened in multiple spots to have it all stay together in a mobile application.
I have a conversion van, and after filling in the windows with polyiso and bringing things even, I used simple i/8 trim sheets.  Nice and flexible.

My insulation varies from 1 1/2 inch to 3 inch.
We have a class C , custom built so similar to the way a step van interior could be built out. The walls and ceiling are 1/8" lauan plywood and the floor is 3/4" plywood. The wall and ceiling panels are glued or screwed into the metal framing of the house box or the wood framing of interior dividing walls. We put wood bracing up between the framing before attaching the 1/8" lauan in places where we thought we might want to put grab bars or hooks. We're happy with both the thickness of the plywood on all of the surfaces and the way it's attached.
I've got a step van with flat walls and roof; no contouring required.

It sounds like people are using way thinner materials than I've got in mind (1/4 seems minimal to me; 3/8 about right for walls), but they're much more densely attached to rigid framing than my plan.

The interior plywood panels will be attached to each other using thin angle metal along all edges, and flat strips of metal at flat seams. There will also be several floor-to-ceiling cabinets a foot or two deep. I reckon by the time it's done that this interior box will be reasonably sturdy on its own, in addition to being pushed out against the insulation (in turn wedged quite tight against the van body) during construction. I don't think it'll rattle, and if it does, I can always add wood or metal bracing?

The reason for having it float is to minimize thermal bridging. Once it's finished (according to current plans), the only metal that contacts both inside and outside air will be the rear and possibly front door handles, and a couple of electrical cords.
ok I see I thought you had a regular van. highdesertranger
Where are you going to be that insulation is that critical? I I think I'd use more polyiso and leave off the plywood altogether. Bob
I used 1/4'' in most places, 3/4'' on the wall that has hooks and a hatch so it wouldn't feel flimsy.

The 1/4'' doesn't sag except for the ceiling, which I reduced by wedging temporary dutchmen posts while I was fiberglassing everything.
In something that moves and flexes, like a vehicle, it's better to build your cabinets so they anchor to the floor. That way they can't fall down. Then anchor the backs of the cabinets to the metal ribs of the vehicle to keep them from tipping front to back, side to side.

My ceiling is 1/8 inch plywood screwed to 1x2s running the length of the roof. The 1x2s are screwed to the roof ribs. That gave me space for two inches of insulation.

My walls are similar, with 1x2s running the length of the van and 2 inches of insulation, only I used 1/8 inch fiber reinforced polyester -- FRP -- with the lumpy side turned inward. I used it because it's very flexible and resists punctures, rips and dings better than 1/8 inch plywood (and which bare polyiso won't). I also painted it a color I like.

Since you're doing a step van, which I assume has flat walls and ceiling, then bendability isn't really an issue. Also, your average home improvement centr probably won't carry 1/8 plywood. You'd need to go to a dedicated lumber yard. But if you just want to skin the interior and not depend on mounting anything to just the plywood, then luan paneling will serve just fine.
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