Need some guidance on internal build-out - insulation, walls, and floor

[iamatesla]

Hey I'm new here, and plan to make a whole thread for this specific conversion - but in general I'm working on my first Skoolie - 2001 TC 2000 bus as base platform.

It was a former police response / operations center vehicle so was kitted out as basically office space inside before. Interior was disgusting though - dirty unclean-able carpet walls and rats had gotten in and made a mess. So - i've ripped just about the entire interior out to start fresh.

I'm at a bit of a loss now though for my next step and could use some feedback / advice

1. Biggest issue right now - should I insulate more? The bus has metal outside walls, and metal inside walls with about 1.5 to 2 inches of insulation between. Spray foam on the outside bottom of floor same thickness. So it is fully insulated, but not very well. I can't remove the metal interior walls - but I could make a wood internal frame that allows me to add another inch or 2 of insulation to the walls (lots of work though and takes up more interior space) - something like this

2. Unfortunately the metal support beams have no thermal bridging protection - they will also conduct outside temp straight to the metal inside walls unless I add something more.

1. Any stylistic recommendations for floor, inside walls, and roof if I want an aesthetic inline to the imagery on this youtube channel that I like a lot?

its sort of retro-futuristic / mid-century modern / frank lloyd wright esque.

I am leaning toward a lot of wood inside, but I am worried if I do wood floors, wood siding, and wood ceiling it'll be way too much wood and just look like a cabin in the woods which I don't quite want.

Basically, I'm asking what would ya'll do next haha - Thanks and looking forward to being part of this community!

 

[nikitis]

So I'd do it like this if you are concerned about thermal bridging to that degree:

(I misspelled furring in the picture so ignore that) Screw a wood block into the hat channel. Add a layer of insulation within the width of the wood block, and then attach a furring strip to the wood block for your walls to attach too. This reduce the thermal bridging to small points (wood blocks) instead of the whole line of the hat channel.

In your case it looks like you already have a thin layer of closed cell spray foam, so if you are looking to save money, you could avoid adding an extra layer of insulation but if you wanted to increase the R value even more you could add some foam board where you would put the wood block.

 

[TheHubbardBus]

I'm assuming when you say you can't remove the interior walls, what you really mean is either YOU can't (with your tools/time/budget/abilities), or you choose not to. Not bashing you in any way here, just pointing out that in the world of bus building anything is possible (though may or may not be advisable). That said, you've definitely got more going on in that regard than your average 'skoolie'.

I view that inner skin as effectively the same as the outer skin, considering how much surface area exists between the two for direct conduction. The insulation between the two has some impact, but I can't imagine it being much at all.

If you can give up the space, it would certainly be best to insulate over the top of it. If you're not removing the interior sheet you don't really have any other option (other than not insulating further at all).

Keep in mind that (grossly simplifying), all insulation really does is slow heat transfer. The slower the transfer, the less energy you need to input per unit time to maintain a desired temp. So if you're able/willing to just throw more juice at the problem, you can be totally comfortable with zero insulation. Practically speaking, however, that usually isn't feasible (and certainly not efficient), particularly if you're planning on being in locations where shore power would not be available.

 

[Rucker]

I used to finish full basements by gluing rigid foam to the concrete, then running strapping over the top of that to secure sheetrock. Looks like that might be a viable approach to your rig.

I would definitely add another 1.5" of rigid insulation.

 

[Jon1371usmc]

I also would like to know the reasoning of not removing the inner sheet metal. Me personally, You're already there, why not take it a step further and do it right. I would not build another wall on top of the current wall assembly. You're already in a bus, square footage is at a premium if not just for having a wider walkway between furnishings on either side, or deeper cabinets, etc. But it's your bus so do as you please. And if you're going off-grid, you're going to want the bus to be fully insulated to save on battery storage and/or diesel fuel if planning to run a diesel heater for heat. If you don't do it right now, are you going to regret it once the bus is complete and it feels like an oven in the summer and a fridge in the winter? Not to mention, if you spray foam you can use the spray foam as a vapor barrier as long as it's the right type and thickness, which will stop water condensing inside your wall cavities that could lead to rot, mold. Just something to think about

 

[TheHubbardBus]

I also would like to know the reasoning of not removing the inner sheet metal. Me personally, You're already there, why not take it a step further and do it right.

@Jon1371usmc, I didn't include your entire quote, but allow me to preface my thoughts with the following: I agree with you pretty much 100%. It's what we did, and I'm glad we did it.

That said, I do believe it's not as cut and dried as 'right' and 'wrong'. As with all things, there are trade-offs. Those interior sheets are responsible for a lot of the strength school buses are famous for. That's not to say a school bus with the interior sheet removed isn't still a strong structure, particularly when compared to factory RVs. And it's also not to say you can't potentially gain some of the lost strength back with creative building practices. But at the end of the day, a bus with the interior sheet intact is going to be in a better position to keep occupants safe in a worst-case scenario. How much better I couldn't say, but... better.

That, and it's a whole lot more time/work/$$. For some people, the juice isn't worth the squeeze.

 

[nikitis]

I would just add some xps or polyiso as he has spray foam behind it already, keep the existing metal wall, don't cut it out. That metal wall is going to thermal bridge though pretty badly, but since it's inside I'd want another layer over the inner sheet metal.

 

[iamatesla]

Thanks for the feedback on this - it's helping me a ton!

A few things. @TheHubbardBus you're correct - I "could" remove the internal walls, and am considering it somewhat, but I really really really do not want to for a few reasons. One - they're riveted on with multiple thousands of rivets. Two - they're really installed well from the standpoint that I do not think I could ever get the same structural quality back into place myself; the internal steel wall structure is definitely adding support/rigidity - this thing is crazy solid. Even the ceiling steel panels are super solid, bent to the correct curves, and perfectly aligned; i have no clue if this is normal bus construction or not but its very well done.

Maybe i'll remove one steel panel just to see how difficult it is, and get a better estimate for the work removing all of them will require.

Based on the recommendations here, it seems the path forward regardless is to then add wood furring strips on the hat channels and build out a new internal wood wall structure this way. Also then applying another 1.5-ish inches of insulation on top of the existing spray foam insulation.

If I'm going to add more insulation in any scenario, I'll have to take up more internal space regardless. So removing the steel internal walls in the best case will likely save at most an inch of overall width.

Currently leaning toward keeping the steel walls, framing out inside with wood which will likely consume what - maybe 2 to 3 inches? of width from the internal space - and covering all the steel with probably (glued on?) XPS rigid foam before my final walls.

 

[nikitis]

Naw, you could simply add like a 1.5inch framing, screw into the metal, and fill the square gaps you create with the framing with 1in xps or polyiso, then use an OSB, and screw the OSB wood into the wood frame you made. This can also leave you slight room for wiring and cabling behind the OSB. Additionally wiring will be between the xps and OSB rather than against a metal sheet. Which would be safer IMO. If you got a short in one of the wires it could maybe make the bus shell go hot electrically.