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Old 12-06-2015, 04:43 PM   #1
Mini-Skoolie
 
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Smile creating a "green" bus conversion from scratch....

Hello friends, my name is Jamie, I'm new to the board and have recently purchased a 1986 International 72 passenger bus with the inside already stripped down and sealed with rustolem. Now the fun begins!

Since I plan on avoiding traditional construction items like plywood, I'm hoping to get some advice from all of you here to turn this bus into an awesome super custom "green" RV for my family and I. So here's where I'm at:

Planning on screwing 2x4's width-wise through the metal floor using the holes that are already there (from where the seats were bolted in). Will I need to insulate the screws on the outside and/or inside to prevent condensation?

Planning on using either rigid board insulation between the 2x4's or mineral wool as a more "green" option. I'm concerned about having enough R-value; two layers of the board insulation only gives R-10, but that's all that will fit in the 1 1/2" of space provided by the 2x4's. What do you think of this insulation idea or do you think something like spray in foam is better for the floor? What about a vapor barrier?

Planning on framing the walls up to to the bottom of the windows with more 2x4's before installing any flooring material. Then planning on insulating the walls with denim batts.....comments?

Planning on using tongue in groove hardwood flooring directly above the 2x4's without a sub-floor to avoid the plywood. Also plan on using the same flooring material for the walls (I found a great deal on ebay!). Do you think this will work well?

For my framing, I will need to bolt 2x4's through the ceiling at certain locations. What is the best way to do this? Special roofing screws or? Then I plan on sealing with spray foam insulation or maybe denim with a vapor barrier and covering the ceiling with more flooring material. Comments and/or other/better ideas?

Thank you so much everyone. This much of the project should keep me busy for sometime
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Old 12-06-2015, 07:04 PM   #2
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Hey, Jamie.

I'm in the process of going through my bus, and am certainly not experienced like the others that will reply, but a couple of things stood out in your post:

Screwing through the floor:
I seriously do not recommend penetrating the floor if you can avoid it. Seal those holes up and glue those 2x4s in place. If you still would rather screw them down, you must be using some HUGE screws. The holes in my floor are about 1/2" diameter where the seats were. If you mean bolting through the floor, I would crawl up under the bus and look where those holes are. You will have a very hard time finding them all, and a harder time making sure they will seal properly. Absolutely seal anything that penetrates the body on both sides. A problem with the floor is that it will flex, and slowly compromise the seals on the screws or bolts. If you use bolts, put washers on each side of the metal floor with a gob of sealant so when you tighten them down, they smush the sealant. Of course, washers on the inside of the bus will raise the 2x4 off the floor, so you'll want to countersink a space for the washers. How will you make sure the screw or bolt lines up with the hole in the floor? Drilling a pilot hole from the underside will be pretty much impossible in all locations as you will discover crawling under the bus. Be sure to water-seal all of those 2x4s if you still plan on going this route.

Rigid board insulation (I don't know anything about mineral wool):
I would like to know what rigid board insulation is R10 at 1 1/2". Don't expect those numbers to be true. Some of the R ratings are based on having an air gap between the board and the wall, sometimes up to 1 foot of total space. I thought about using rigid board on my floor as well, but I am leaning towards closed cell spray foam now. The price difference is pretty extreme, but the end result is superior to anything else I have read. The closed cell spray foam will be its own vapor barrier. On the negative side, the spray foam will take a lot of time to trim down properly to make a flat surface.

Flooring directly over the rigid foam:

Two layers of rigid board is going to compress faster than the 2x4, making your flooring warp. Using plywood would more evenly distribute the weight of footsteps on the floor, minimizing the flex between the 2x4s.

Screwing through the ceiling:
Sort of the same warning here as the floor, but even moreso. The underside of the bus won't see as much moisture as the roof will due to rain. If you can attach the verticals to the ribs of the bus rather than penetraing the roof, you pretty much eliminate any leaking opportunities. Again, the bus flexes as you drive and with temperature, flexing the 2x4s that then flex the screws. I know I will have to go through the ceiling on my bus in quite few locations to secure solar panels and a roof rack, but I will be bolting through, all drilled holes rust treated, washers with automotive tape, and both sides caulked with butyl. I bet mine still won't be 100% waterproof.

It's a fun and involved project! Take your time to do your best and you'll be rewarded with years of trouble-free usage. Read a lot too.
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Old 12-06-2015, 07:23 PM   #3
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Thanks, that's super helpful. I would love to avoid going through that thick steel if at all possible. I guess it seems like glue wouldn't be strong enough, but if that's the standard.....well, great!
Any other ideas are welcome
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Old 12-06-2015, 07:40 PM   #4
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Well, I really wouldn't say there's a "standard." Others will post here before long.
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Old 12-06-2015, 07:40 PM   #5
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Why the aversion to plywood? 2x4's are even more traditional than plywood.

Consider your headroom after all that insulation. Most school buses aren't very generous to start with.

Cut your 2x4's in half width-wise. That will give you more insulation, less thermal bridge and cut your cost in half. Glue them down to the floor. All the weight you'll be placing on the floor will keep it in place even if the adhesive fails.

Many here have laid down the pink foam insulation with plywood "floating" directly above with no wood supports at all.

The instructions included with my polyiso insulation (with a foil side) recommended a 1/8" air gap to the warm side. The foil is supposed to reflect heat back. Two layers of 3/4" polyiso boards will give you R10.

For the ceiling, definitely don't screw through the roof. Screw into the inner roof ribs instead.

Most people remove the factory installed fiberglass batts because of their willingness to grow mold. If you don't go with spray-in insulation be sure to seal the edges of your insulation boards to keep humidity from condensing between the outer steel body and the insul. boards.

I'm interested in your green approach. What else do you have in mind?
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Old 12-06-2015, 08:50 PM   #6
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To clarify, I'm trying to avoid anything that contains formaldehyde or other chemicals that offgas. 2x4's are just wood (although some are treated but not with anything that offgasses) but plywood of course contains lots of formaldehyde containing glue. The foam insulation is suspect enough although seem to be less of a risk than the plywood. That is actually the biggest reason I bought a bus to convert into an RV; old RV's are cheap but contain tons of off-gassing products.
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Old 12-06-2015, 11:31 PM   #7
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You definitely can float the subfloor over the foam, directly on top with no need to use the 'sleepers' under your floor. Poly-Iso foam board has an r value of 7 per inch and is the best for this application. I see it in up to 2" thick at Home Depot near me for about $32 for a 4x8' sheet. You gain and loose heat in the vertical plane, so (with headroom in mind) put as much insulation in the floor and ceiling as possible, with an emphasis on the ceiling. I have 3" of poly iso in my floor and 3" of spray foam in my walls and ceiling and its amazing but I still have cold floors (45* floors when its 18* outside).

As for your framing, you should look into a technique thats more accurately called strapping. You should not need to bolt through your roof to have a secure framing system. Look for screws that are specifically designed to attach wood to metal. They are self-tapping and will establish a very secure connection.

Most osb and plywood sold at big box stores doesn't have formaldehyde anymore. You can find the safety info from manufacturers. Id prefer using 1" thick plywood ripped down to about 2" wide strips for my strapping--it will take screws and holes without splitting and doesn't have any issues with warping and is plenty rigid when the spray foam sets up around it. Spray foam is like concrete made of air. I love it.

You will need some kind of subfloor over your foam, if only to make a strong gluing surface. You could do sheet steel and glue your flooring on top of it or you can use plywood (best) or osb (not best) and glue/nail your flooring on top.

Im building 2 buses for people right now and this is the approach we are going with. Using a steel subfloor saves precious inches for insulation, but it will arguably feel colder underfoot as it is a great conductor of heat--in this case, away from you. Unless you have in floor heating, this isn't really a good thing.

There's no reason to bump your walls out a full 1.5" by using 2x4s for wall construction unless you really want that extra insulation. I highly recommend the aforementioned strapping technique. I should make a video....

Dont use denim or other absorbant material for insulation--it will grow mold, rust, and trouble. Stick with spray foam all around. It is superior in almost every way.

Also, I would build your subfloor before doing your walls.

Did you strip out the inner metal skins and pull the old insulation?

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Old 12-07-2015, 11:33 AM   #8
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I'm planning on looking into formaldahyde free plywood as well as the offgassing of liquid nails for the glue later today. I'll keep you all posted
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Old 12-07-2015, 11:41 AM   #9
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And no, I was not planning on ripping out the metal skins and insulation....everything seems pretty well contained in there and it seems like it would be alot of extra work to do. I guess the benefit would be 3 total extra inches times 28ft, or a total of 7 extra square feet of floor space. I suppose in my final designing if I need it, we'll do it......
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Old 12-07-2015, 12:56 PM   #10
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Quote:
Originally Posted by jwilcox View Post
And no, I was not planning on ripping out the metal skins and insulation....everything seems pretty well contained in there and it seems like it would be alot of extra work to do. I guess the benefit would be 3 total extra inches times 28ft, or a total of 7 extra square feet of floor space. I suppose in my final designing if I need it, we'll do it......
The benefit is also to remove the potential for mold growth while increasing your insulation's R value. The fiberglass batting does absolutely nothing to insulate the bus as it is now.

The missus and I pulled the ceiling panels back to front and were damned glad we did. There was mold (and dirt and other assorted crud) in the batting-
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