How thick are your inner walls?

[BlackNBlue]

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.

 

[highdesertranger]

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

 

[Almost There]

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.

 

[GotSmart]

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.

https://vanlivingforum.com/Thread-Rebuild-91-Dodge-short-van

 

[rvwandering]

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.

 

[BlackNBlue]

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.

 

[highdesertranger]

ok I see I thought you had a regular van. highdesertranger

 

[akrvbob]

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

 

[Svenn]

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.

 

[MrNoodly]

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.

 

[Every Road Leads Home]

I can't personally see a reason to not attach the walls directly to the vehicle. I don't think the amount of thermal bridging from a few dozen screws would even be a measurable temperature difference. However the potential drawbacks seem very measurable......anything in a vehicle not secured makes noise, the more noise you hear from things rattling the less comfortable the ride is, an hour ride commute in a work van with tools non stop rattling is actually tiresome......it literally causes fatigue. This is an extreme example, but there is no way you'll get those walls tight enough and if there's even a 1/16th of an inch gap somewhere, the wood is going to squeak and drive you nuts everywhere you go. Unsecured things are also much more dangerous in a car accident, you most certainly don't want 1500 lbs of interior van space to come flying at you in a head on collision.

 

[BlackNBlue]

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.

Yup, the cabinets are all either actually on the floor, or supported by pillars (2x2?) that in turn press down into the floor. They'll also be screwed into the ceiling for lateral support.

As I read people's responses, I'm starting to wonder how much of anything heavy will really be screwed into the plywood itself. Its main purpose is to keep the polyiso from getting dinged (and to look nicer than 20+ year old reclaimed insulation), and 1/4" seems plenty for that even on the floor.

I can't personally see a reason to not attach the walls directly to the vehicle. I don't think the amount of thermal bridging from a few dozen screws would even be a measurable temperature difference.

I don't have them in front of me, but I ran some numbers and determined that the thermal bridging effect is actually quite significant, something like a 25% loss of R-value for wood screws that penetrate all the way through at 1' square spacing. Also, they would stick outside because the van has no braces to screw into, except on the roof; the walls are just huge flat sheets of 1/8" aluminum.

As for noise, driving this thing already requires earplugs (zero sound deadening anywhere, and the cab is a huge metal resonance chamber)... I'm not going to worry about a few rattles, and I figure I can always add interior bracing.

 

[Tussah]

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.

https://vanlivingforum.com/Thread-Rebuild-91-Dodge-short-van

That really looks great!   Where did you find the 1/8 trim sheets?  I can't seem to find it on the Home Depot or Lowes websites.

 

[highdesertranger]

lumber supply or make your own. highdesertranger

 

[TrainChaser]

Maybe I'm missing something obvious here, but.... Why would you want to build a freestanding box inside of a box??? If you're building for the long term, I'm thinking that the contant movement is likely to start loosening things.

You don't mention if your box has metal ribs or not. But if it doesn't, you could use 2x4s like in the photo below, where you think you would need support for cupboards or shelves, and fill the rest with polyiso (etc), and cover w/panelling. Just mark the floors where your uprights are, and make a point of drilling into them.

This guy is insulating for a refrigerated farm truck, but the principals should be the same (you're just keeping the cold outside instead of inside):
http://farmhack.org/sites/default/files/f350.Framing1.jpg

 

[maki2]

Your largest heat loss issue is not going to be thermal bridging as wood is not that much of a thermal bridge. But if it concerns you it is very easy to solve and it can be done without adding any significant weight. Just go to Home Depot or Lowes or any hardware store and purchase rolls of thin, adhesive backed, close cell foam weather stripping. Stick it to all the metal ribs before you attach the horizontal wood stringers. 

Place the horizontal stringers at the height where you will be securing your cabinetry. For instance at the upper edge of the cabinets you can install a horizontal 1x3 or 1x4. The upper edge of that stringer should be an inch or so above the level where the countertop is so that you have some extra support behind your wall paneling to help support the backsplash.

It is the stringers that will do the work of supporting what you attach to the walls, that and also securing things with sheet metal screws into the ribs.  It is a big mistake to add thick plywood to the side walls or the roof as it is first of all not needed and second there is the weight issue. You want to conserve on weight where you can both for gas mileage and also so you can have a decent sized battery bank. You will find that the batteries are far more essential for keeping your life comfortable than heavy plywood walls. The floor can be 5/8" plywood. You don't really need 3/4" because the support is coming from the steel underneath.

Plywood is not all that great of an insulator, the foam does that more effectively at a lower cost and lower weight.

I would say that the majority of people who set out to do a van build go crazy and somehow think it has to be done the way a house is with lots of heavy timbers. But they seem to forget that the van is built with steel structure or in the case of some step vans aluminum structure which is much stronger than wood. Let your van be the strength it was designed to be, just finish it off inside for looks and comfort. You really don't need to increase the strength of the van itself by using thick plywood.

 

[highdesertranger]

"I would say that the majority of people who set out to do a van build go crazy and somehow think it has to be done the way a house is with lots of heavy timbers."

so true. there is no need for 2x4's or anything bigger.

keep it light, 1x2's, 2x2's and plywood is all you need.

highdesertranger

 

[nature lover]

Since I am fat I try to keep the rest of the van lighter. 2x4s are too heavy 2X2s are plenty strong enough. Once I screwed furring strips into the vans ribs and stapled foam backed carpet to the strips. The furring strips will bend with the contours of the van ribs. I should have stretched the carpet tighter but it turned out all right by adding new longer staples as needed. I found out that you need to hold the stapler tight against the carpet when firing or they do not go in tight. (anyone smarter than me would have known that)

 

[nature lover]

Just remembered another story - I seem to have too much time on my hands. As a bus tour operator I took a group to Howe Caverns in upstate NY and while we were many feet blow ground one of the ladies in the group asked our guide how think the walls of the cave were.

 

[Thomas]

On my Chevy van I screwed 2" strips of 3/4" plywood to the steel studs - as a place to attach to, and to achieve a uniform contour.  Then I insulated with expanding foam.  For the walls I used tongue and groove cedar, horizontally using liquid nails, and brads to hold stuff in place while the glue set up.  I had to grind off any foam that stood proud, and any areas where the foam fell short and left a portion of wall unsupported, I just stuffed in some carpet padding I had on hand.  It's held up perfectly for 11 years.  On the foam insulation piece, I learned that supplementing a thin area with carpet padding is much more fun than grinding off excess foam.  Try to avoid grinding off foam - the dust gets into your soul.

I'm now studying on building out a box truck as a stealth motor home.  I plan on framing the box with 2 x 3's - the cabinetry version of studs - attached to the aluminum box studs or to the box sheathing itself with construction adhesive, incorporating adequate cross members.  The boxes I'm shopping for are kind of wimpy.  The walls and ceiling were only meant to support themselves.  Interior walls and ceilings that do not support the box are hanging from the box, and the box was not intended for that.  So, a box within a box.  I'd like to insulate with rigid foam panels, glued in to my framing with expanding foam, leaving an airspace between my insulation and the box skin.  Expanding foam as a primary insulation might be great - it's lightweight and becomes rigid, so would probably count as supporting the box as much as hanging from it, but that's a lot of foam.  I dunno. Maybe. Someone please tell me.  For wall board I'm thinking 1/4" sanded plywood or luan.   Light and tight is what I'm going for.