Which materials and techniques for bus interiors?

[Artor]

Experienced residential builder here: For your interior walls, don't use 3/4 plywood, as it's more material than you need. You could go with half inch, or even 3/8" ply, as long as you get some AC or shop wood. Don't use CDX. You could get your walls down to 2 3/4" that way, gaining space and losing nothing.

 

[Artor]

I should read more closely before replying. I didn't catch that you were talking about your exterior walls. But DO put a vapor barrier behind your surface. Moisture can't get out through the metal, but it will condense there, and drip behind your insulation. The vapor barrier will keep moisture in the living space which should usually be warm, and prevent the condensation. Proper ventilation will allow it to escape.

 

[As We Go.]

Look at the aluminum frame work in my album. Very rigid and light weight. I use self tapping screws, aluminum angle and 3/8 plywood.

 

[Artor]

About what I was planning on myself. How sturdy did it come out? Just a single layer of ply, or did you box it in both sides?

 

[dzl_]

I should read more closely before replying. I didn't catch that you were talking about your exterior walls. But DO put a vapor barrier behind your surface. Moisture can't get out through the metal, but it will condense there, and drip behind your insulation. The vapor barrier will keep moisture in the living space which should usually be warm, and prevent the condensation. Proper ventilation will allow it to escape.

Should the proper order of things (when using wooden interior walls) from exterior to interior be:


Metal external skin --> Insulation --> Vapor barrier --> Interior skin


I imagine in some cases the insulation and the vapor barrier would be the same layer, or in others the interior skin would be the vapor barrier.

 

[Artor]

Yes, if your insulation is a completely sealed impermeable sheet. Either sprayed in, or closely fit rigid foam with taped seams will work. Failing that, a sheet of Tyvek or visqueen before your facing surface will do.

 

[kidharris]

I have noticed that a lot of folks like to build with the same materials and methods they would use in the interior of a conventional residence. I suppose that is the path of least resistance, to go with the techniques and materials that we are most familiar with and which are cheap and easy to acquire. I see people building out their interiors with 2x framing lumber and drywall and basically recreating the design of homes built years ago when carpenters did what they knew best, turn a pile of lumber into finished dwelling.

I’m thinking that if weight matters, there may be lesions to be learned from examples of aircraft, and the trailer industry. I am looking for ideas for using metal channel like trailer walls are made with and finishing with pre-painted aluminum sheets or fiberglass reinforced panel (FRP) and accenting with strips of stainless steel or aluminum. Maybe even pop-riveting cheap Luan plywood ($14/sheet) to sheet metal studs. I am already leaning towards furring out my exterior walls with 2 x 2 (nominal) metal studs which would give me 3 1/2 inches total wall thickness. For insulation It looks like foam is the only choice for the climates where temperatures go sub-freezing. For days on end. I just can’t see how anything else can work. Any kind of permeable insulation like mineral wool or fiberglass bats is going to be a problem. You cannot put a vapor barrier between the living space and the insulation because every insulated space has to have some way to dry, to rid it self of the moisture which will inevitably get in either from leaky windows, screw penetrations or whatever. The wall certainly are not going to dry towards the exterior. Moisture is not going to pass through the sheet metal outer panels and if you put a vapor barrier on the inner face of the wall you will be trapping that moisture in the wall where it is going to cause rust or grow mold. So it’s either foam or spend winters in warm climates.

Seems like you are trying to think outside of the box so I am going to point out a few things here for you to consider.



When cars and air planes were first being designed wood was commonly used for several reasons. People were used to working with it, so the tooling and skills sets were already in place. The other big driver was that pound for pound wood is stronger than steel. So is aluminum. Wood has several serious disadvantages - volume (to be the same strength as a given amount of steel requires a larger, but lighter, volume of wood, which is not good where space is at a premium), low to no tensile strength, and water absorption causes weight gain, loss of strength, rot, and dimensional instability. Result - as the price of aluminum came down aluminum edged wood out of most uses in both industries.

Wood is also a much better insulator than steel (would be better for your furring strips).

You didn't say what kind of trailers that you were talking about, but if it was commercial cargo trailers you should realize that those walls with "metal channel" could be metal E-Track Tie-Down Systems that are built to hold thousands of pounds of cargo on moveable load bars.

All of the common temperature insulation have 2 things in common. The materials have low coefficients of conductivity and have dead air spaces. Of the 2 properties, dead air spaces is responsible for most of the insulating ability. To illustrate how this works, think of a thermos jug (Dewar flask). It has the ultimate dead air space (a vacuum) but is usually built out of 2 really terrible, but cheap, insulators - a metal and/or glass.

Dead air spaces greater than .5-.75 inch allow convection currents to start moving and are no longer dead air spaces. When ever possible dead air spaces should be sealed and another gas,such as nitrogen or argon (lower specific heat and no phase change ability at normal living temperatures, in other words - no water/humidity), is substituted for air. A vacuum is better than dead air but requires more structural strength to maintain, which is why it almost always involves spheres or cylinders.

Despite what some people here think, radiant barriers work great in the right circumstances/setup. That's why the aforementioned thermos jugs have mirrored glass. The vacuum stops conduction and convection heat loses/gains and the mirror stops radiant heat loses/gains. The connections/seals between the inner and outer walls can be and usually are, some less conductive material.

You don't have to live in a thermous to be comfortable, after all they say that snow is a pretty good insulator. People have used moveable insulation such as blankets, curtains, and clothes for thousands of years.

If everyone is so worried about the inside of the metal skin getting wet and rusting, why don't they paint it before insulating?

Good luck with you thinking/plan, a good plan is invaluable.

 

[wrenchtech]

I was looking at a high-end residential design magazine called Dwell. They carry it at my local library. I haven’t paid much attention to it because I have not been interested in modern design until now. Now I am thinking the bus might be a good place to break out some modern design touches. I saw a home interior in that magazine finished in “A” grade birch veneer plywood with a clear finish so that the natural wood is what you see. Seems like a great solution to me. The modern design embraces large expenses with minimal trim. Keeping it simple yet refined.

 

[o1marc]

Seems like you are trying to think outside of the box so I am going to point out a few things here for you to consider.



When cars and air planes were first being designed wood was commonly used for several reasons. People were used to working with it, so the tooling and skills sets were already in place. The other big driver was that pound for pound wood is stronger than steel. So is aluminum. Wood has several serious disadvantages - volume (to be the same strength as a given amount of steel requires a larger, but lighter, volume of wood, which is not good where space is at a premium), low to no tensile strength, and water absorption causes weight gain, loss of strength, rot, and dimensional instability. Result - as the price of aluminum came down aluminum edged wood out of most uses in both industries..

Wood is also a much better insulator than steel (would be better for your furring strips).

You didn't say what kind of trailers that you were talking about, but if it was commercial cargo trailers you should realize that those walls with "metal channel" could be metal E-Track Tie-Down Systems that are built to hold thousands of pounds of cargo on moveable load bars.

All of the common temperature insulation have 2 things in common. The materials have low coefficients of conductivity and have dead air spaces. Of the 2 properties, dead air spaces is responsible for most of the insulating ability. To illustrate how this works, think of a thermos jug (Dewar flask). It has the ultimate dead air space (a vacuum) but is usually built out of 2 really terrible, but cheap, insulators - a metal and/or glass.

Dead air spaces greater than .5-.75 inch allow convection currents to start moving and are no longer dead air spaces. When ever possible dead air spaces should be sealed and another gas,such as nitrogen or argon (lower specific heat and no phase change ability at normal living temperatures, in other words - no water/humidity), is substituted for air. A vacuum is better than dead air but requires more structural strength to maintain, which is why it almost always involves spheres or cylinders.

Despite what some people here think, radiant barriers work great in the right circumstances/setup. That's why the aforementioned thermos jugs have mirrored glass. The vacuum stops conduction and convection heat loses/gains and the mirror stops radiant heat loses/gains. The connections/seals between the inner and outer walls can be and usually are, some less conductive material.

You don't have to live in a thermous to be comfortable, after all they say that snow is a pretty good insulator. People have used moveable insulation such as blankets, curtains, and clothes for thousands of years.



Good luck with you thinking/plan, a good plan is invaluable.

"pound for pound wood is stronger than steel."

In what universe?:whistling:

 

[kidharris]

I think the RV industry has the weight factor down well. You can't get much lighter then wood paneling and 2x2s. One problem with light weight is it usually turns out to be rather flimsy.

You could get into carbon fiber, aluminum, titanium(rocket ship) and shave lbs and oz's here and there but it would get very expensive very fast. Reminds me of a school bus I saw that someone built from a airplane junk yard.

Well said....

 

[kidharris]

I framed the bed platform and hanging cabinets with mild-steel angle-iron and square tubing in my bus.

In order of importance to me (most to least):

= less volume - so important to me since my bus is mid-sized

= stronger - just try to crack it...go ahead...just try!

= more durable joints (wooden joints often need additional, expensive !!! angle-brackets or binding strips, or become even more voluminous using wood)

= more flexible - who's the guy that just blew out a windshield by hitting "the mother of all potholes" just this week (as told on this site). Same bus as me. If my body flexes, so do my hanging cabinets.

= recycles better than wood into a usable material when the bus retires.

= lighter weight - better to climb hills with

= cheaper - a 20' stick of 1"×1" angle iron is under $20 here (about $16.80).

Of course I had to learn to use a stick welder. Took a day of practice before I could weld a 1/4"-20 stainless steel nut to a steel bar without destroying the nut or bar. Not too hard.

Now I can install surfaces to the metal frames that have the look I want. Just waiting to find the right lightweight paneling that I like.

Originally I was going to frame it all with wood, but I needed the nuts mentioned above welded to finish my roof-hatch-skylight. Once I realized I could weld, that changed everything.

One 10-foot wooden 2×4 plank: 1.5" × 3.5" × 120" = 630"³
One 10-foot steel angle stick: 0.125" × 0.125" × 120" = 1.874"³
EDIT (whoops, wrong formula):
One 10-foot steel angle stick: (0.125" + 0.125") × 120" = 30"³


One cubic foot is 12" × 12" × 12" = 1720"³

If I framed my bed with wooden 2×4s it would use:

(75" × 4) + (33" × 4) + (18" × 4) = 504" (linear inches: length + width + height for 2×4 planks)


plus additional 2×2 braces:
(11" × 4) = 44"



So:
1.5" × 3.5" × 504" = 2646"³
1.5" × 1.5" × 44" = 24.75"³
2646"³ + 24.75"³ = 2670"³


That's more than 1.5 cubic feet of space I would take up with a wooden frame bed.....more volume than a milk-crate full of stuff. But sometimes all ya need is just that 1/2" of linear space to squeeze your junk into that storage space.


note in the pics, there is also a small sink framed with stainless steel angle iron. It is NOT cheaper at about $80 for 20'. I got a 20' stick for $60 with two slight bends in it. I cut the pieces for the sink avoiding the bends. Also the stainless steel welding sticks are pretty pricey. But all was worth it for a better end-product.

I think sort of like you, only a little crazier (more obsessive) I don't think in terms of cubic feet wasted but more in useable space wasted.


I favor sheet metal cabinets (more useable space internally and externally.


Thin metal pocket doors are also a great space saver


As much stuff as possible should do double duty.


Using the hallway/walk space for other uses. My big, 3'x4' shower is going to be in the hallway (with pocket doors and curtains closing it in) as well as some moveable cabinets, shelving, furniture, etc). Think Rubics Cube.



I have some previous experience with this.



In my previous small home shop I built small, wheeled, metal cabinets to mount many of my bigger table mounted tools (saws, grinders sanders, drill press. welder). These cabinets were pushed back against the walls when not in use and pulled out into the walk way (or taken outside) when I needed to use the tool. I called it my tool garage. It allowed me to have many more tools in my cramped shop, organized, and most importantly, still quickly useable. The heavier tools (mill, lathe, air compressor etc could be permanently placed and the smaller stuff moved if more room was needed to use the tool.


In a 10'x11' bedroom I had a queen size bed, 29 linear foot of book shelves, 15 linear feet of 24" wide desk space with printer, 2 monitors (with 4- file cabinet/office drawers cabs under it with 2 - 28"x24" drawers for the scanner, keyboards, mice, pens, etc, 15' of 24" wide shelf/storage space that held 3 tvs, 1 cabinet on a lazy susan with a 4 pieces component entertainment system, 1 cabinet on a lazy susan with 4 computers with a bunch of AB switches to connect everything to everything (with the lazy susans I could rotate the cabs to get to the wires in back - crazy complicated and insane) There was also 5' of clothes hanging .75" pipe, 1 dorm style fridge, a microwave and a 4 drawer 18"x28" full size file cabinet. under the bed and clothes rack was 16 plastic totes and 3 big suitcases. I still had room in the center for an office chair. There was also plenty of storarge on the 30" shelves and among the things that lived there was a projector and a large office sized paper cutter.



I was trying to figure out how much crap you can put in a small area and still live in it. Problem is a bus is less than 8' wide so to put the same crap into it, I would need to downsize the bed. Definitely doable, since I don't have as much electronics now.



One thing that I determined for sure was that you need at least a 4'x4' open area to be able to operate an office chair and be able to get by and get dressed in the same space. Even that takes practice. Depends on the chair and whether it has arm rests. A small chair might get by with 40"x40"b ut I would still want 4'x4' More space would be needed fora larger chair or 2 people (or else someone is always in the way. Been there and did that and it was annoying but fun).


Other things I learned.
A custom built bed frame that raises the bed up to butt level is easier to get in and out of, better for sex, and gives you more storage room under it.


More electrical outlets than you need is a lot better than stringing cords everywhere. Run your electrical in conduit or plenums. However things change. We seem to be headed towards a cordless future, but stuff still breaks and corded/hardwired stuff provides more security.


Although I didn't try it I think that tubes run in the walls/floor with outlets for a vacuum cleaner and mount the vac out of the way is a good idea. Lower the noise volume, a short hose would be easier to handle, and vacs are much easier to keep small, tightly packed places clean than brooms, a quick touch up is easy.


Use drawers to operate out of and store stuff in whenever possible. For instance if you printer is in a drawer, it not only doesn't get dusty as much but it is easy to get to when you need it. There won't be crap piled on top or around it, plus it is out of sight and the place looks less cluttered which is important in a small place. Another example: Tabletops collect clutter, but if your table top is in a drawer, the clutter goes away when you shut the drawer, plus you can have multiple table tops at different heights.

 

[kidharris]

"pound for pound wood is stronger than steel."

In what universe?:whistling:

The Universe that most of us live in. Look it up smarty:bow:, but keep your mind in gear and perhaps you will realize that the high tensile strength steels that we have to day didn't exist when they started building cars and airplanes. The early cars had wood wheels and cloth covered wood tops. Airplanes were almost entirely cloth covered wood construction because the strength to weight ratio necessary for flight just wasn't there with steel. I am not sure if you could build a steel airplane today even with the modern high tensile strength steels.


As far as I know it has been long understood that a steel beam of the same rectangular cross section dimensions as a wooden beam often couldn't even carry its own weight. Of course dementia could be setting in.


Oh wait... these guys seem to agree


https://skyciv.com/technical/commonely-used-materials-in-structural-engineering/


"Tensile strength. For being a relatively lightweight building material, wood outperforms even steel when it comes to breaking length (or self-support length). Simply put, it can support its own weight better, which allows for larger spaces and fewer necessary supports in some building designs."


Even tho that only took a few minutes, I really don't have the inclination to do your research, so I am going to stop here.


In addition, it is very hard to find a decent piece of wood without a bunch of knots today as compared to a hundred hears ago when they still had access to old growth trees so I can understand your skepticism. While wood is not very strong in tensile strength, tensile strength is not the only measurement of a materials strength.

 

[kidharris]

Look at the aluminum frame work in my album. Very rigid and light weight. I use self tapping screws, aluminum angle and 3/8 plywood.

The contrast of the aluminum and wood door looks good

 

[kidharris]

One of the advantages we have with our school buses over RVs, is that our structures are already very strong. No wooden stick frames with light gauge metal skins and staples. To make a partition wall to close off my bedroom from the rest of the bus I am thinking of using 2 x 3 sheet metal studs, Which are widely available, relatively inexpensive, and easy to work with (no welding required). I could even install them on 1 foot centers instead of the usual 16 inches, to add strength and keep the walls from being wavy.

Thomas has a great point too, I will definitely look at materials available from the marine world, which is very well represented where I am located. They have some sheet products that are waterproof, attractive, and which would be very useful in constructing a bathroom or surfaces in the kitchen.

And more power to you mountain gnome for teaching you. I don’t know what I would do without welding capability. It really opens up opportunities to use a wider selection of materials to build great stuff.

They have a pretty good selection of metal studs and channels at a local big box store near me that I plan to take advantage of.

If I was going to use c studs I would not use the flimsy ones sold at thr big box stores. I would go to a steel wholesaler or drywall wholesaler and see what else was available. Probably need a big city for that though.

 

[BigPaul367]

The beautiful thing about building a Skoolie, is there are no rules. Those who speak of any rules are passing on their knowledge to those who have not yet built for themselves. I have seen the use of SIPs to make three inch walls and 1" square tube to make 1.5 inch walls and that owner sighting the thinner wall leaves more floor space in an already tight format. I have seen Toy Haulers, fifth wheels and skoolies with garages that actually house a small vehicle like a Smart Car, Trike of Motorcycle. 3/4" plywood walls, tongue and groove works well because it can move and shift without pulling apart. One person is using Insulation Foam Sheets to build everything EVERYTHING in his rig, talk about Ultra Light Interiors! There are those who raise the rook and eliminate all the windows to stay warm. One dude replaced the windows he wanted to keep with Vinyl, Dual Pane, Triple Glazed, Windows on the outside and installed another single pane window on the inside because he planned to stay for a year in Alaska and did not want to be cold at all. I tend to say the oldest saying when it comes to such choices, "It is just like building a HotRod, Speed costs, son! How fast do you want to go?" The only thing I have NOT seen yet, is someone who converted to a Hybrid Drive for their Skoolie!

 

[Truthseeker4449]

I'm considering using cardboard coated in expoy with a vinyl covering for my ceiling. Except I probably need more strength to mount speakers in it.

The only thing I have NOT seen yet, is someone who converted to a Hybrid Drive for their Skoolie!

The kits are out there, that's for sure. One of the bus companies that uses my shop has F-550 diesel hybrids. Theirs are from Variable Torque Motors. The motor is a big, green, retarder looking thing spliced into the driveshaft.

 

[kidharris]

I'm considering using cardboard coated in expoy with a vinyl covering for my ceiling. Except I probably need more strength to mount speakers in it.



The kits are out there, that's for sure. One of the bus companies that uses my shop has F-550 diesel hybrids. Theirs are from Variable Torque Motors. The motor is a big, green, retarder looking thing spliced into the driveshaft.

Epoxy as in FRP?

 

[Truthseeker4449]

Epoxy as in FRP?

No, epoxy resin brushed onto single layer cardboard. Though this FRP stuff looks interesting, the next time I swing by Lowes I need to look for it.

 

[musigenesis]

"pound for pound wood is stronger than steel."

In what universe?:whistling:

"Wood is pound-for-pound stronger than steel" is a common claim in my universe, and unlike a lot of common claims here, this one is actually true, the key being the "pound-for-pound" part. Here are the relevant physical properties of the materials:

Eastern White Pine
Tensile strength (parallel to the grain): 11,300 psi
Compressive strength (parallel): 4800 psi
Density: 21.77 pcf

Mild Steel
Tensile strength: 63,800 psi
Compressive strength: (roughly the same as tensile)
Density: 490.75 pcf

A piece of pine with a one-square-inch cross section could hang an 11,300 pound weight without breaking, while a piece of steel with the same one-square-inch cross section could support a 63,800 pound weight, so in an absolute sense steel is obviously stronger than wood (about 5X stronger).

But steel is also much denser than wood, so that piece of 1"x1" cross-section steel will weigh 22.5 times as much (per unit length) as the piece of wood (490.75 pcf / 21.77 pcf = 22.5). If you increased the cross-section of the wood until it weighed the same per unit length as the steel (this is what the "pound-for-pound" bit means), the wood would be 22.5 square inches, or about 4.75"x4.75". A wooden beam with a cross-section this large would be able to support 254,730 pounds (in tension), quite a bit more than the steel of the same weight.

(Wood is less than half as strong in compression as in tension, so steel fares better by comparison there, but is still not as strong as wood pound-for-pound.)

Hope this clears up any confusion on your part!

 

[Phychotron]

Look at the aluminum frame work in my album. Very rigid and light weight. I use self tapping screws, aluminum angle and 3/8 plywood.

Do you insulate the aluminum from the rest of the shell? If the metal is connected to the outside it will act as a heat sink. I've heard of van builders that had well insulated vans with ice cold or blazing hot aluminum framing because they didn't think to isolate the metal framing.