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Old 06-14-2021, 12:54 PM   #1
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Building Science for Skoolies?

Hey yíall, happy to be a part of this awesome community ! Just jumping into the skoolie life and seems there isnít much detail out there for designing a proper assembly that is resilient against moisture and mold. Iím also seeing a LOT of folks using materials and methods that would trap moisture and are not accounting for any vapor transfer.
Excuse the length of this post, but I feel this topic is super important due to the apparent wide spread confusion of materials, vapor barriers, and the amount of work and money people are investing into this process. Would love to hear the input of other experienced builders (especially with bus experience) to come up with the best practice for insulating and sealing a skoolie. Iím an architect and builder (for regular homes) and have done a lot of research on building science and the thermodynamics of typical floor and wall assemblies. A bus is obviously a different ball game, having a painted steel shell (continuous vapor barrier) which throws a little more of a challenge as far as managing vapor transfer, mold and condensation than a conventional home. Itís also a massive thermal bridge, allowing heat or cold to transfer to the interior via conduction of the metal. This is a huge concern that seems to be overlooked in most bus builds, and most certainly needs to be addressed to avoid condensation and a comfortable interior.
For any floor or wall assembly, itís important to maintain a clear path for vapor transfer to allow the wall or floor to dry out to both the interior and exterior (depending on the climate and season).
Considering this will be mobile, itís hard to plan for a specific climate due to it always changing, so the more forgiving your assemblies are with vapor permeability, the better. In this type of situation (mixed climate with alternating paths of vapor drive) you would want to avoid any vapor barriers to allow the assembly to dry out in any direction. Obviously this isnít possible for a bus since the painted metal vapor barrier is pre existing, but you most certainly donít want to be adding additional vapor barriers within the assembly because youíre only option is to allow the assembly to dry toward the interior.
The most ideal situation would be to have exterior insulation to eliminate the dew point from occurring inside the assembly (and allowing condensation to form on the interior side of the metal), but this would be pretty hard to achieve while preserving an existing outer shell.
It seems the norm for these builds is to use rigid foam insulation (usually with a foil faced vapor barrier) directly over the metal floor and walls. This seems problematic because there is no venting behind the insulation, and does not allow the moisture to dry out when condensation is formed due to warm air reaching the cold metal surface. Not only is there not an air space for drying, your trapping the moisture between 2 vapor barriers (the foil faced foam and the painted metal). This will result in a build up of moisture causing mold, rot and rust. This problem can be even worse when batt or loose fill insulation is used, which would most certainly saturate the insulation with moisture and in a short time have a minimal resistance to heat transfer. (Batt insulation ALWAYS needs to have an air space to dry out if placed against an exterior vapor barrier, such as a roofing membrane or your painted metal skin)
Just like any regular home, the only way you can properly insulate a closed unvented assembly (with an exterior vapor barrier) and prevent the surface from reaching the dew point temperature and forming condensation is by using spray foam insulation directly over the interior side of the metal, or rigid foam on the exterior side. This will keep the dew point occurring in the middle of the insulation and can allow the vapor to dry out of the assembly.
So clearly some kind of spray foam insulation (I like airkrete because it is a sustainable foam with the same r value as petroleum based foams minus the off gasing) is pretty much the only option for walls and ceiling if you donít want condensation forming inside your assembly. You would also need some kind of thermal break in addition, as leaving the ribs uninsulated without any thermal break would surely cause a large amount of heat transfer and condensation. The only alternative for the ceiling that I can see is to install rigid foam over the exterior roof, then installing a support structure over the foam for solar or a roof deck. This saves time and money for leaving the original ceiling intact and eliminates the massive thermal bridging that occurs in these buses.
For floors, I really like the idea of spray foaming the exterior underside of the metal floor as this will save head clearance, stop your metal from reaching the dew point temperature and forming condensation, and will act as a secondary barrier for allowing moisture to penetrate through the floor. This would require some extra work with prepping your metal so the foam can adhere properly (sand blasting and then using a rust encapsulating paint like por 15) , but would undoubtedly be a superior product in the end. Has anyone have any insight or experience with these methods?
My second choice would be to use a NON FOIL FACED foam like XPS to allow the moisture to dry out to the interior. Itís important to get a continuous uninterrupted layer of insulation over the floor to eliminate the thermal bridging. I donít understand why people are using furring strips over the metal and insulating in between . This is only causing more thermal bridging, less insulation, and allowing areas to form condensation and a nice organic medium for mold growth. Rigid foam is designed to withstand pressure when evenly distributed, so you can just put your plywood directly over the foam. If your putting an oil based coating over your finished floor or using vinyl or some other similar non permeable surface, be sure to leave areas around your floor (such as under cabinets or furniture) that are permeable like just painting with acrylic latex paint.
Any professionals out there or someone with experience in properly insulating vehicles please chime in !! Thanks for reading my long ass rant lol 🙏

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Old 06-14-2021, 02:35 PM   #2
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Wow, detailed post! Thanks for that.

Just picking a random section for comment: floor insulation. It's been discussed here a few times. The idea of foam insulation on the underside of the bus seemed...impractical. I have twenty years of road grime on every surface under there, and the actual amount of floor that is accessible and not blocked by drive gear, wires, cables or the bus frame is miniscule. Not to mention the challenges if you actually need to repair a wire or component that got slimed during the insulation process.

The second alternative, rigid insulation on the floor, is more practical especially if there is headroom in the bus. Most shuttle buses have that, except turtletops. Most school buses don't have that, which forces the specter of a roof raise.

I have a shuttle bus, but left the industrial-strength vinyl intact. I live in California, so cold weather operation is not a big factor. Also, I have a diesel heater that can warm a gymnasium. We'll see how I feel about my choices after a trip into the Sierras this winter.
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Old 06-14-2021, 02:38 PM   #3
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And one more: vapor barriers. If the bus will regularly see subfreezing temps or excessively wet climates I can't think of anything more important than preventing interior moisture from touching the metal or fiberglass skin of the bus.

I don't have those concerns where I live but have been really interested in hearing someone who does need to prevent condensation and who has installed a vapor barrier discuss the actual results after a season or two in the cold (or wet).
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Old 06-14-2021, 05:58 PM   #4
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Much of what you have discussed can be addressed by using materials which may better fit the conduction, convection & radiation. Seal the outer shell. Really seal it. There are hidden leaks, crevices, hollows, and wicking. Consider fiberglass extrusions run perpendicular to all exposed interior ribs.

Hat or z-bar ceiling, channel rail under the window. Insulated standoffs, if you wish to add those. Spray foam them all. Floors: fiberglass I-beams with owens 250 foamborad or spray it. Better yet, 400 foamboard the whole floor and hole saw 2"dia fiberglass rod cut to desired "height". Adheasive drop/tap into hole. Bridge them, set floor. GP Densdeck everything, I'm into wood finish. Wait, windows, ugh. Closed cell backer rod, various sizes. Did I mention, 8-10 types of sealant, firestop, and adhesives. Shade, albeit solar panels, trees, decks may perform more than reflective paint. Maybe, idk, I haven't tested any paints.

I bet we have all fantasized better ways than what we actually do. That's the best I have, so far. I am actually doing some of these not-so-ridiculous steps.
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Old 06-16-2021, 04:35 PM   #5
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Quote:
Originally Posted by plantbus View Post
Any professionals out there or someone with experience in properly insulating vehicles please chime in !! Thanks for reading my long ass rant lol 🙏
I don't have any of that, but that's not going to stop me from giving my opinion

I've been thinking for months on how I am going to approach it. Here's the compromise I've settled on:

1. Let everything breathe. Condensation from the floor, walls and windows will be allowed to diffuse INTO the bus where I will deal with it. Condensation from the ceiling will be vented passively. More on that later.

2. The floor of my bus is treated plywood. It's rubber coated on the bottom and has survived 12 years of Ohio winters without any issues. I therefore consider it to be a watertight barrier on the outside. I'm not going to claim it is an insulator, but it is slightly less bad than a steel floor, and the dew point is not going to be a firm spot on the surface and will move in and out. Third, the floor is covered with ribbed vinyl. I will keep that as an actual breathing channel under my interior insulator (bare XPS foam). While the plywood rubber coating on the outside is tight, the vinyl side is porous. I will not seal the floor seams and perforate them every 12" or so.

3. I have only limited acreage of problematic walls. Those ARE metal (aluminum or stainless). Since walls are by definition vertical, I expect less thermal loss there anyway and use only 2 stacked sheets of 3/4" XPS. The outer sheet is glued to the metal, the inner sheet is free for breathing. I will seal the edges of the walls to prevent any generated moisture between the floor and floor foam to be channeled between the walls and the outer layer of the wall foam.

3. I will heat cold surfaces - the windows specifically. I have a transit bus with tons of square feet of single pane glass. That is never going to be a good energy equation. I am ducting the heating so that I can literally heat the windows enough so they don't fog up, and the moisture gets absorbed into the air. We are going to have to see how much energy that takes, but it will be in the kilowatts when all the factors are against us.

4. The ceiling: My bus already has 1.5" of styrofoam in the ceiling, but the stainless frame every two feet renders it essentially pointless. So I'm going to have a half-inch "attic space" between my interior insulation and the current bus ceiling, and passively vent it to the outside. My bus ceiling becomes the new "sheltered outside". Easy!

5. I'll avoid producing vapor inside the bus. Breathing and cooking are essential, showers are not. Just kidding, but I'll keep the shower at negative pressure so the humid air gets exhausted almost entirely. No propane or any other combustion products inside the bus.

6. I'm rather environmentally conscious, but I'm going to massively over-dimension the heating system, and move air. During cold winters, the outside air is dry, so I am just going to replace the inside air several times per hour. All the hot moist air is replaced with cold dry air, that then needs to be heated, but so be it.

7. I'm leaving room for energy recovery. I'll make sure that, if it turns out that the energy cost due to forced air replacement is too high, I can recover most of the heat. I've built a house in Scandinavia, and there it is the norm that you channel the incoming and outgoing air through a heat exchanger. Over 90% of recovery is easily doable.

8. I'm leaving room for actively drying the air. If it turns out that I can't get the RH low enough on an ongoing basis, I'll put in a dehumidification system. Due to the fact that I need to budget electricity for that, which is much more expensive than diesel generated heat, comparatively speaking, I leave that for last.

Bert
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Old 06-27-2021, 02:49 PM   #6
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Join Date: Aug 2020
Location: Washington State
Posts: 19
Year: 2006
Coachwork: El Dorado Aerotech
Chassis: Ford E-450
Engine: 6.0 L Powerstroke
I'm not an expert, but this guy is.

https://www.stitcher.com/show/vansfo...irgoe-55563968

Edit: this is the more detailed technical description: https://youtu.be/hDZBJw7cV2U

Curious what else you guys come up with. I am working on my insulation now, and have changed my mind several times already on how to do it.
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Old 06-27-2021, 09:29 PM   #7
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Thatís a good link, thanks for posting!
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Old 07-08-2021, 11:47 AM   #8
Mini-Skoolie
 
Join Date: Jun 2021
Posts: 61
I built my live-aboard vehicles since the late 1960s, over a half-century.
.
My goal (aka RequirementsStatement):
* travel rather than build,
* doing interesting activities with interesting people...
* ...instead of parked in a stand-still house driveway measuring thrice while fussing with one inconsequential detail, forever filing-to-fit and perpetually painting-to-match.
Accordingly, I often initiate a build on-the-road -- with a camp-cot, a camp-stove, food and clothes in crates -- allowing the build to organically evolve as an intimate part of the journey.
.
My process:
* can I build with suggestions from chums using 'found' objects?
* can I modify my careful-laid plans (cue -- laughing gods...) as I adapt to situations and events?
* am I 'one' with my environment instead of 'brute forcing' it?
Picture 'rustic hand-made doings instead of Shiny! perfect Shiny! thinking-about-doing ordered on-line from a Shiny! catalog'.
.
My gentle suggestion to new builders quaged in the Shiny! place:
* might you be over-thinking this?
.
Sometimes, occasionally but not always, excess planning is an attempt to camouflage a lack of confidence in abilities.
How to gain confidence?
One suggestion:
* join a caravan of experienced travelers, then
* observe, volunteer, ask, listen, then
* learn about tools, equipment, techniques
Cook some, potlatch often, be the first to worsh some dishes.
This can be a form of 'earning trust'.
.
Inevitably, you become the mentor, showing the ropes to new folks.
Happens every time.
Doing instead of thinking-about-doing.
.
And then, almost before you know it, you are closing-in on your seventh decade, and you get to post windy know-it-all answers to forums on TheWorldWideWeb!
.
My final suggestion:
* take up harmonica and quit them tuba lessons
Is this an analogy to pare belongings so a smaller rig fits your 'new' you?
Could be.
Is this an analogy to 'quiet the monkey-mind' and enjoy the moment?
Nah.
.
PS:
Inner-city, Boston, Miami, Seattle, Toronto, Tiananmen?
What!
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Old 07-08-2021, 01:11 PM   #9
Mini-Skoolie
 
Join Date: Aug 2020
Location: Washington State
Posts: 19
Year: 2006
Coachwork: El Dorado Aerotech
Chassis: Ford E-450
Engine: 6.0 L Powerstroke
Quote:
Originally Posted by LargeMargeInBaja View Post
I built my live-aboard vehicles since the late 1960s, over a half-century.
.
My goal (aka RequirementsStatement):
* travel rather than build,
* doing interesting activities with interesting people...
* ...instead of parked in a stand-still house driveway measuring thrice while fussing with one inconsequential detail, forever filing-to-fit and perpetually painting-to-match.
Accordingly, I often initiate a build on-the-road -- with a camp-cot, a camp-stove, food and clothes in crates -- allowing the build to organically evolve as an intimate part of the journey.
.
My process:
* can I build with suggestions from chums using 'found' objects?
* can I modify my careful-laid plans (cue -- laughing gods...) as I adapt to situations and events?
* am I 'one' with my environment instead of 'brute forcing' it?
Picture 'rustic hand-made doings instead of Shiny! perfect Shiny! thinking-about-doing ordered on-line from a Shiny! catalog'.
.
My gentle suggestion to new builders quaged in the Shiny! place:
* might you be over-thinking this?
.
Sometimes, occasionally but not always, excess planning is an attempt to camouflage a lack of confidence in abilities.
How to gain confidence?
One suggestion:
* join a caravan of experienced travelers, then
* observe, volunteer, ask, listen, then
* learn about tools, equipment, techniques
Cook some, potlatch often, be the first to worsh some dishes.
This can be a form of 'earning trust'.
.
Inevitably, you become the mentor, showing the ropes to new folks.
Happens every time.
Doing instead of thinking-about-doing.
.
And then, almost before you know it, you are closing-in on your seventh decade, and you get to post windy know-it-all answers to forums on TheWorldWideWeb!
.
My final suggestion:
* take up harmonica and quit them tuba lessons
Is this an analogy to pare belongings so a smaller rig fits your 'new' you?
Could be.
Is this an analogy to 'quiet the monkey-mind' and enjoy the moment?
Nah.
.
PS:
Inner-city, Boston, Miami, Seattle, Toronto, Tiananmen?
What!
Nice! Perhaps not the answer we all wanted, but the answer we all needed.
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Old 07-08-2021, 06:31 PM   #10
Bus Nut
 
Join Date: Apr 2020
Location: Northern California (Sacramento)
Posts: 380
Year: 1999
Chassis: Ford E450
Quote:
Originally Posted by LargeMargeInBaja View Post
I built my live-aboard vehicles since the late 1960s, over a half-century.
.
.
My gentle suggestion to new builders quaged in the Shiny! place:
* might you be over-thinking this?
.
Absolutely! And I love your thoughts-most best words I've seen regarding build versus enjoy.
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