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Old 09-07-2022, 07:07 PM   #1
Mini-Skoolie
 
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Avoiding condensation on backside of interior walls/framing

Is there any recommendations or learned lessons with interior walls/framing touching the metal ribs of busses?
Seems like condensation would occur there overnight, and then get sucked up by the wood creating rot and mold.

Do people lay out plastic wrap as a vapor barrier or seal the wood to prevent this?

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Old 09-08-2022, 12:05 AM   #2
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my approach

keeping the steel walls and roof for now... using heat that does not put off any condensation and being able to run ac system to de humidify the air.

I am letting is sweat and I will deal with it as we go.

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Old 09-08-2022, 07:40 AM   #3
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Quote:
Originally Posted by Woodams View Post
Is there any recommendations or learned lessons with interior walls/framing touching the metal ribs of busses?
Seems like condensation would occur there overnight, and then get sucked up by the wood creating rot and mold.

Do people lay out plastic wrap as a vapor barrier or seal the wood to prevent this?

in my opinion if you are framing the inside of the bus you take down the interior steels (down to the chair rail). and spray foam the bus then build out over the spray foamed shell...



otherwise I think not framing and building false walls inside is the way to go..
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Old 09-08-2022, 08:37 AM   #4
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Originally Posted by cadillackid View Post
in my opinion if you are framing the inside of the bus you take down the interior steels (down to the chair rail). and spray foam the bus then build out over the spray foamed shell...



otherwise I think not framing and building false walls inside is the way to go..
Right, that’s my plan, but my suspicion is that laying plywood over the sprayfoamed walls (screwed to the metal ribs) would allow condensation to collect on the ribs and then soak into the walls.
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Old 09-08-2022, 09:03 AM   #5
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Coat it before install? My opinion also does a no structural wood or sub floor / wall should be anything less than marine grade. Your bus will probably leak.. no not after you build it but in a monsoon 3 years from now ? Very possibly.. true marine grade lasts a long time in pretty wet conditions
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Old 09-08-2022, 12:24 PM   #6
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Relevant thread: https://www.skoolie.net/forums/f13/i...ure-35983.html

Search condensation, vapor barrier in the forum for more.
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Old 09-15-2022, 02:02 PM   #7
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Ventilation.
.
Could you install a series of 'eave vents' designed for a stand-still house?
These allow air to move through the enclosed space of the attic, reducing the innate moisture accumulation inherent to temperature differences.
.
Real-World:
For our ExpeditionVehicle, the square box was a dry-van, no interior beyond the wall and ceiling structure.
2003, we insulated obsessively excessive, so we understood the potential for condensation.
Accordingly, our first layer of insulation is an adhesive-back acoustic, engineered to shed water without growing molds.
.
Additionally, 24/7/360°, we have two windows open on opposite walls.
We think the reason for condensation is a difference in temperature.
Accordingly, we minimize the temperature difference between our inside and the outside.
We are outside most of our day, we are comfortable with a cooler rig.
.
Hx:
During a half-century of make-do camping in lesser rigs, we experimented with all kinds of combinations to reduce condensation.
This is our latest attempt.
Nearly two decades full-time live-aboard in our ExpeditionVehicle.
We will let you know how it goes...
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Old 09-16-2022, 07:28 AM   #8
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Right, that’s my plan, but my suspicion is that laying plywood over the sprayfoamed walls (screwed to the metal ribs) would allow condensation to collect on the ribs and then soak into the walls.

You can insulate the ribs and the walls anywhere wood will directly touch with 3m 77 spray adhesive and sill plate insulation.
Apply the spray to the steel and the insulation. Give it a bit to tack up and you can form the thin sill plate insulation to the bus.
You can attach ribs to it and any wall studs.
Frame it out and then spray foam.
I never let any wood ever touch any steel directly.
You need that barrier to stop exactly what you have mentioned with condensation forming between the wood and the ribs or the sides of the bus.
Sill plate insulation is cheap and a easy way to add a extra barrier of protection.
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Old 09-16-2022, 12:25 PM   #9
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Quote:
Originally Posted by Jay Brand View Post
You can insulate the ribs and the walls anywhere wood will directly touch with 3m 77 spray adhesive and sill plate insulation.
Apply the spray to the steel and the insulation. Give it a bit to tack up and you can form the thin sill plate insulation to the bus.
You can attach ribs to it and any wall studs.
Frame it out and then spray foam.
I never let any wood ever touch any steel directly.
You need that barrier to stop exactly what you have mentioned with condensation forming between the wood and the ribs or the sides of the bus.
Sill plate insulation is cheap and a easy way to add a extra barrier of protection.
Sill plate insulation is a great suggestion to prevent direct contact.
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Old 09-17-2022, 06:46 PM   #10
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We sprayed foam against the shell and are avoiding lumber as much as possible. LP Legacy T&G sub-floor is moisture and mold resistant . I’m using 1/4” foam as a thermal break anywhere it touches the exterior framing to reduce the possible condensation. We will use FRP or some other non-porous material to skin the walls. A dehumidifier will help the mini-split with humidity.
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Old 09-17-2022, 07:06 PM   #11
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spray foam!

the coverage of spray foam removes any surface that will condensate. i don't know why, but the sprayfoam stays dry.

i have spray foam in my bus,
i have spray foam in a outdoor building.

moisture isnt an issue inside.

last year, i re-did a van that had used havelock wool for insulation. the gaps in the wall where the wool slipped or wasnt tight against a metal surface condensated a lot. the floor of the van was flooded and holding a half inch of water and soggy havelock wool when we pulled it up.

i cleaned all that up and spray foamed the van.
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Old 09-17-2022, 10:38 PM   #12
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foam tape

Quote:
Originally Posted by Jay Brand View Post
You can insulate the ribs and the walls anywhere wood will directly touch with 3m 77 spray adhesive and sill plate insulation.
Apply the spray to the steel and the insulation. Give it a bit to tack up and you can form the thin sill plate insulation to the bus.
You can attach ribs to it and any wall studs.
Frame it out and then spray foam.
I never let any wood ever touch any steel directly.
You need that barrier to stop exactly what you have mentioned with condensation forming between the wood and the ribs or the sides of the bus.
Sill plate insulation is cheap and a easy way to add a extra barrier of protection.
I spray foamed and then used a double sided foam tape about an eighth inch thick and spread a bubble wrap type insulation over the whole thing before starting anything. There is no wood touching metal. The only place there is metal to metal are the few Tex screws that hold a few 2x3 framing material to the ribs. I really don't think that's going to cause a problem with condensation.
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Old 09-17-2022, 11:17 PM   #13
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We have been using our bus for 4 years now and we usually have 3 adults and 3 kids sleeping in there. We have spray foam throughout the walls and ceiling and the metal ribs on the walls are still exposed. We usually have our fantastic fan on speed 1 through the night, I keep it probably around 70 but I’ve never had any condensation anywhere. And we’re in a cold climate. I wonder what set ups people have that do get condensation.

Only time water gets in is when the rain leaks in through my sunroof or the emergency exit hatch. Oh and the time a whole gallon of milk flew out of the fridge and burst open when I took a corner too fast.
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Old 09-18-2022, 06:28 AM   #14
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To prevent condensation, I highly recommend against spray in foam insulation. I worked in the rv capital of the world in Elkhart, IN, for over 20 years and we did testing with it and had different reps come in and it was never able to meet industry standards. The under belly was the only pace it's used and it's only in a set few places but if the underbelly was protected, then it didnt get it. The R-value of spray in isn't as good as fiberglass, caused warping, caused moisture between walls and foam which turns to rust, and the big one was fire, the melting and dripping causing more damage. What I've done for customs because starting in 97 until 2016 before moving to Asheville, on the side I did custom schoolie rv conversions for customers, and to solve condensation I always eliminated the factory school bus windows and installed rv windows, did walls ceiling and floor in a liquid vapor barrier, eliminated the factory walls and ceiling, used fiberglass or wool insulation, and depending on the size of the bus I used one or two maxxair fans. One of my biggest issues is factory windows. I all so often would see people come to me with a schoolie they had done or done themselves and they'd want to know how to keep the windows from being full of condensation that runs and drips on their wood walls and floors because it's doing what water does turning to mold and the wall/floor starts to get soft and you know the rest.
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Old 09-18-2022, 09:33 AM   #15
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To prevent condensation, I highly recommend against spray in foam insulation.....
---------------

Hi, Jason. Welcome to Skoolie.net. Always great to have new members.

What type of bus do you have?
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Old 09-30-2022, 11:46 AM   #16
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---------------

Hi, Jason. Welcome to Skoolie.net. Always great to have new members.

What type of bus do you have?
I just sold my 2012 6 window short bus, it was a Chevy dually with a duramax. Then a couple wks ago I purchased a 2006 Chevy C5500 7 window mid-bus with duramax. I haven't done much yet other than removed all of the windows, removed back and 2 right side doors, seats, floor, ceiling, and walls are all stripped down. Once this season of drag racing is over, I won't be traveling all over the country so I'll be able to get it done. I use them to pull my car/enclosed trailer around the country and then when that's done I like to travel and chill for a couple months. What kind of schoolie do you have?
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