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Old 05-18-2009, 02:38 PM   #1
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Insulate the Exterior?

Speaking of insulation... most folks on this forum work their insulation from the inside, losing valuable inches of living space. Has anyone thought of putting insulation on the OUTSIDE and reskinning the bus with the original panels, instead of doing that to the inside?

Sounds radical, but you'd only be adding 2 to 4 inches extra to the exterior width and who measures the outside width of a bus? I would think this would allow at least 3" of insulation. Maybe spray an inch to seal the air leaks and add 2" of board foam to smooth the sides, then reskin with the original siding. Any gaps can be capped with regular sheet metal, making the transition look smooth and natural.

Am I totally crazy to step that far outside the box? Can anyone think of disadvantages to doing it this way (besides working outside in the elements)?
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Old 05-18-2009, 04:48 PM   #2
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Re: Insulate the Exterior?

I would think the costs could be kept down by re-using the original skin of the bus, just as others reuse the interior skin. The only extra metal that would be needed would be transition pieces to make up the difference between the old exterior width and the new width.

Does the 8ft 6in rule include the rear-view mirrors?
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Old 05-18-2009, 07:06 PM   #3
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Re: Insulate the Exterior?

I've thought about it. I've considered using the spray on polyurethane roofing foam that i've seen sprayed on metal storage buildings, hangar workshops and similar. It's supposed to be very efficient per thickness inch of coverage, and nicely waterproofs things as well. I would think spray on polyurethane would be vastly superior to any other form of external insulation for a driving bus, due to it's toughness (at least vs something like styrofoam) and from all accounts the R-value of spray on foam is superior to the same R-value of say fiberglass batt in the actual real world because the urethane foam is totally windproof and moisture proof whereas fiberglass batt rapidly loses insulation value with the slightest air penetration or with moisture or sometimes even at extreme temperature differentials. It even adds structural strength, sound deadening, it wont rot, some minor impact resistance against minor hail (at least vs raw paint), waterproofs your roof, would potentially allow you to change the shape of the bus while keeping it smooth (ie - build a wooden rounded nose extension to try make the air go around the side and just urethane over it without looking like a tacked on wooden box), would probably fix leaks for any holes you cut in your roof regardless of reason, etc etc.

It's also alot healthier as far as I can tell, fiberglass fibers are bad like asbestos is bad, rock wool bunches up, and styrofoam will be harder to fit to the rounded shapes and isnt durable by itself so wouldn't work on the outside without a whole new outer shell built around it. Some info - http://www.sprayfoam.org/index.php?page_id=198 There are some DIY/spray at home setups too I think. I hear anecdotal stories of people insulating with spray foam and cutting energy bills in half, even though they had the same R value in fiberglass previously. 4 inches of foam is basically enough for a walk in commercial freezer.

Spray foam would nicely water/air seal around less than perfect craftmanship for removing schoolbus windows and putting in more RV like windows especially if they were better insulated windows, without having to dink around with an eternity of trying to make fiberglass body putty look right and repainting. The foam seals things.

I may be the first to actually try this, i'll be posting more information as I research it. If you beat me to it please share.

Since there's a 102" width limit, and I get the impression most busses are 96" (is this correct?) you should be able to put on two inches on the outside with no problem. (3 is risky because if you go 3 and 1/4" youre over the legal limit) You could make it thicker on the top since heat tends to get lost going up. You could put two inches outside and two inches inside on the sides if you wanted to drive in the arctic or northern canada. (Since I actually do, I actually might)

Someone wanting serious insulation could even spray both outside and inside the bus. I may do exactly that with how cold it gets in minnesota or start with just the outside. Although spray on foam costs more per inch of insulation than say styrofoam, the simplicity of install, speed of spraying it on, use around curves, exterior durability and the rest probably make it worth the extra cost. I'm consider 'splurging' on this even if I could DIY other insulation cheaper.

A fair bit of energy can be lost through the bottom however too - houses lose 17% of energy through the foundation. This is likely reduced with a bus being raised off the ground, but if it were possible to stick an inch of something up under it without too much difficulty i'd do that too. Or maybe have wind skirts or something to stop air blowing under it which pulls the heat away from around it.

http://www.sprayfoam.org/index.php?page_id=198


I've also considered using stacked strawbales for the 'home' i'm planning to make though. (basically plan to stack freestanding bales as a form of garage so that I have R50 outside the bus plus the windbreak) You wont be driving with that but bales in farming regions are cheap, around R40-R50, can freestand up to reasonable heights and even support some roofing weight. (which I plan to make out of corrugated steel) They dont really harbor mice (too dense to easily dig into), just bees sometimes, they dont really degrade in the wind or snow blown from the side as long as they have overhead coverage and arent sitting in water and can airdry to the atmosphere (they rot if they sit in water or get rained on top, but blown rain from the side dries out - some Nebraska exposed strawbale walls are still here 100 years later), and since the bus is meant to be a closed container anyways it provides a second layer of protection in case mice got inside the bales.
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Old 05-18-2009, 07:17 PM   #4
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Re: Insulate the Exterior?

Quote:
Originally Posted by TygerCub
Speaking of insulation... most folks on this forum work their insulation from the inside, losing valuable inches of living space. Has anyone thought of putting insulation on the OUTSIDE and reskinning the bus with the original panels, instead of doing that to the inside?
I've actually given this a lot of thought and worked out a lot of the details with my dad and a good friend of mine that usually shoots holes in most of my plans.

Things to consider (or at least, things I keep in mind while planning)...

. The strength of a school bus during a rollover is related to the design of the body. There's the steel tubes that run up and over and down the other side. There's the skin on the inside. There's the skin on the outside. Then there's the rub rails. Yes, even the windows are somewhat important to the structural integrity.

. When insulating, you want a thermal break. Metal to metal contact is a thermal bridge, allowing easy transfer of heat from one side to the other.

. You must choose wisely when you choose your foam, as some variants of foam will act like a sponge when any moisture is nearby. moisture behind your metal will end up being a bad thing.

. School busses are built to protect kids. Many of them are held together by 30 gazillion screws or rivets or a combination of the two. Think about that for a minute.

My first thought for insulation involved removing the outer skin, extending the ribs with wood, insulating, then installing the skin to the wood ribs. Wood would still be a thermal bridge, but not as bad as metal to metal. After looking closely at my bus, I realized that type of project could turn into a suicide mission. Did I mention the 30 gazillion screws and rivets? Perhaps I should mention the 30 gazillion screws and rivets! Seriously, there are 30 gazillion screws and rivets holding that stuff on!

Also, I realized that doing that would reduce the strength of the bus. Let's face it, wood is not as strong as steel.

I basically abandoned the idea for a while. Then one day while sitting in the yard staring at the bus, I had an epiphany. Why not add a second skin?

I figure that using wood ribs *not* directly over the existing metal ribs will deflect the heat bridges. I can screw into the wood ribs from the inside of the original skin. I can mold the wood to fit over the rub rails and other strength adding bends in the sides. Then, on the outside, I could use some kind of thin metal or even fiberglass to be the outer skin. The outer skin would be nice and smooth (mostly), and have no importance to the structural integrity. Also, with the bus being already close to 8' wide on the exterior, you can add 3" per side and still be in the 8'6" clearance.

There are still a LOT of logistical details involved. These include sourcing large sheets of skin and finding sufficient help to manhandle them into place and screw or rivet them in place. With wooden ribs, I believe it would be screws.

The outer skin would not need to be as tough as the original outer skin.

An expanding foam insulation would give a good bang/buck for insulation value as well as adding a lot of sound deadening. Plus, it could help keep the skin smooth with the pressure when installed.

My current hope for my own bus is to be able to do this to the outside, and a 1" to 1.5" interior insulated wall, resulting in 4 layers. That would be new inside, original inside, original outside, and new outside. That's 3 layers of insulation between those 4 layers of "wall". This provides multiple thermal breaks and keeps the original structural integrity. Hopefully it'll help keep the weight down, add lots of noise dampening, and of course, insulate quite well.

Yes, I know that sounds extreme. I'm planning to build my bus to be able to survive wintering in alaska and summering in florida. If I can make it efficient enough for me to survive those extremes, then I know it will do quite well where ever I find myself. I don't expect anyone else to be as extreme about this as I currently plan to be.

Bear in mind I'm just barely started on my conversion. Time, money, and energy constraints might prompt a change of plans. Or the harsh onset of reality... nah, can't let that affect anything!

Also, for the roof, I'm considering making it closer to 4" to 6" thick between the original skin and the second skin.

On the side, there are several compartments that would not mate well with a second skin. It took a bit of thinking to come up with a good solution for that. We're thinking we can bring the second skin in a taper to the first skin at the bottom of the rub rail that is along the original floor. Extra insulation like that just isn't needed for my storage compartments, as my plan involves having plenty of storage inside thanks to a roof raise.

I realize my final bus is going to look a bit funky. Hopefully it won't be distasteful. But even if it is, I hope a nice paint job will help disguise any blemishes.

TygerCub, if you want to deal with the 30 gazillion screws and rivets, then by all means, don't let me stop you.

Keep thinking outside the box. Even bad ideas can prompt good ones, and I've seen you posting a lot of good ideas.

jim
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Old 05-18-2009, 07:43 PM   #5
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Re: Insulate the Exterior?

Jim G., it sounds like you've thought of this carefully, did you catch my comments about spray on polyurethane roofing foam? Can you think of any reason that wouldn't work? No reskinning, no new ribs, no abnormal and distastefully excessive thickness, just a soft squishy surface that adheres well to metal and is basically done the same day.

Only downside I see is you cant paint it to look the color you want, the color options for spray foam are probably going to be limited. But then again if you have an already yellow schoolbus the cost of the spray foam saves you the cost of having to paint it too, so...
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Old 05-18-2009, 09:28 PM   #6
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Re: Insulate the Exterior?

baadpuppy,
Yeah, the rivets thing did terrify me a bit. But I was thinking a cut off blade on an angle grinder might make it a little easier. (maybe just a tiny bit?... 30 gazillion, did ya say?)

Anyway... point taken about the rivet. (30 gazillion... wow). Also, great point about the structural integrity. I really do like the idea of your three layer approach. BUT... what about finding any potential bad spots between the new and old skins? That's one of the reasons I thought of removing one layer in the first place (either the exterior or interior). Find all the bad stuff and clear it out, then replace the insulation with something more substantial = spray foam = and complete the project as normal. Are there as many rivets inside as out?

nearhomeless,
Roofing foam is good stuff, but... I've seen a lot of the roofing insulating foam where I work. It's not very smooth - looks a lot like fluffy pillows in the "rough". That can be overcome with some creative shaping, a lot of patience, and a willingness to make a grand mess (imagine foam snow storm). One of the biggest drawbacks of using foam anywhere is it must be protected from UV radiation. Sunlight will turn any foam brittle, and spray on roofing foam is no different. Even the stuff used in monolithic domes is protected by a vinyl cover, or a specialty acrylic paint.

But... the more I read on the high density foams, the more I'm liking the idea. Many of these foams are formulated to withstand the pressure of walking, which means - with the right protective coating - they would withstand the everyday "casual" contact of RV life.

And with the sculpting possibilities.... oooo, my creative mind wanders!

Check out http://www.dura-foam.com for just one company's information.
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Old 05-18-2009, 11:29 PM   #7
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Re: Insulate the Exterior?

Quote:
Originally Posted by TygerCub
I really do like the idea of your three layer approach. BUT... what about finding any potential bad spots between the new and old skins? That's one of the reasons I thought of removing one layer in the first place (either the exterior or interior). Find all the bad stuff and clear it out, then replace the insulation with something more substantial = spray foam = and complete the project as normal. Are there as many rivets inside as out?
There are only about 19 gazillion rivets and screws inside.

In my case, I plan to completely remove all the existing interior sheeting during the addition of the new exterior sheeting. This will let me pull out the old fiberglass batting (which is either a: kinda wet and bedraggled or b: not where it was originally installed) and put in some good high-R insulation. After all that, I would put the interior sheeting back, and build up from there.

Another reason for ripping it that far apart is exactly what you said: finding the trouble before it is big trouble. I figure once it is insulated and sealed, I should have many years (2-3 decades? I can hope!) before I have to worry about any problems in the interior of the wall.

Of course, I'm also striving for 0 holes through the roof and upper walls aside from windows. I hate windows because they're poor insulators and also because they let in too much light. But, I refuse to live in a death chamber, so I will have windows that will all also function as emergency egress.

Yes, I know 0 holes is virtually unattainable, but I can strive for it.

jim
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Old 05-18-2009, 11:30 PM   #8
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Re: Insulate the Exterior?

Quote:
Originally Posted by nearhomeless
Jim G., it sounds like you've thought of this carefully, did you catch my comments about spray on polyurethane roofing foam? Can you think of any reason that wouldn't work? No reskinning, no new ribs, no abnormal and distastefully excessive thickness, just a soft squishy surface that adheres well to metal and is basically done the same day.

Only downside I see is you cant paint it to look the color you want, the color options for spray foam are probably going to be limited. But then again if you have an already yellow schoolbus the cost of the spray foam saves you the cost of having to paint it too, so...
I don't know anything about those products, but I'd rather have more on the outside than *just* foam. After all, some of these roads have some vicious trees just waiting to gouge a chunk of your foam right off your bus!

I wouldn't mind seeing someone give it a shot though. If it looked like a success, I'd consider it.

jim
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Old 05-19-2009, 12:43 AM   #9
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Re: Insulate the Exterior?

Well if the insulation foam isn't very flat i'll just call my bus the Rolling Cloud and be at that.

I figure if you walk on the stuff it's got to be fairly tough.

Trees might chip it, but you just spray on some more foam to patch it up.

I see foam with 10 year warranties, typical expected lives of 15 years, and the older roofing foams still holding up 30 years later. Surely that would outlast most people's busses. If UV killed it that fast you wouldn't see it on roofs ever.

Think of it this way - look at how good your typical coffee cup insulates. Thats about 1/8" an inch of foam and youre holding near boiling coffee in your hand without injury. Your typical camping cooler is maybe 1/2" inch of foam. If you open it even slightly everything melts, if it stays closed it stays cold. (air infiltration is more often the cause of lost heat instead of poor insulation) Foam is awesome. The biggest problem I see is conduction, since metal conducts heat spraying foam on half of it doesnt insulate all of it. But isn't that already occuring no matter what you insulate your bus with? It's quite possible that 1 inch of foam sprayed everywhere (including under) would be worth more than 3 inches on the sides/5 inches on the roof/nothing under just to stop the conduction.

The only downsides I see to spray foam is that it was tried on RV's in the past and in some cases didnt work - the moving metal turned the stuff to dust, on some RV's (not all) over many years. Search the Airstream boards, they complain about it. However those are flimsy RV's, were talking solid sturdy school busses. The other complaint is formaldehyde - but I think that was used in the past and there are non FH foams you can use now, i'll have to recheck. So i'm not saying i'm perfectly sold on my own idea, I just want the discussion to continue.

It just seems that the effort of building a whole new external shell just to contain insulation is almost overkill.
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Old 05-23-2009, 03:11 AM   #10
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Re: Insulate the Exterior?

I might have missed it, but you are forgetting that you HAVE to have something on the outside of the foam to protect it...

Skin it while its still wet so it holds on to the skin, then ryno-line the b*sturd. The stuff is known for being a very durable surface. I remember reading on their site that they are even using it as an external form of insulation... Supposedly it can reflect a bit of the thermal heat.

If it works to reflect even the tiniest amount of heat, its worth it. Not only that, think of the saving on paint and carwash soap over the life of the vehicle. Ryno-lining is rinse and forget.
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