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Old 11-10-2018, 09:02 PM   #1
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Condensation Confusion

Hi, I am working on my skoolie, Celestina. She is a 40’ Thomas 1998, flat nose, front engine.
I have stripped out floors, side panels and ceiling panels. I put down 2”x3” battens on the floor with construction adhesive and then put down 2” rigid pink foam board and then 1/2” plywood. I added 1-1/2” rigid pink foam in the side walls. I started adding 1-1/2” pink foam to the ceiling and then today I noticed moisture on the underside of the metal ceiling. I am worried about condensation. I have been searching through past threads and am more confused.

I am in Oregon and plan to be working on the bus this winter and hope to take off this summer. While I am working on the bus this winter, do I need to worry about condensation? If I finish the rigid foam insulation and then add furring boards to the ribs for a ceiling, will I have a mess of condensation and rust forming behind the foam boards? How can I prevent a rain fall in my bus? Any advice for a first time skoolie.
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Old 11-10-2018, 11:20 PM   #2
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Just my $0.02. Condensation can be an indicator of leakage, however, more often than not, condensation comes from a major difference between inside and outside temperatures. If your bus has emergency roof hatches, make certain they are tightly closed and sealed. Ditto on the rear emergency door. Check weatherstripping on all hatches and doors. If your bus has auxiliary air-conditioners, there could be drafts getting through them. Still another thought, if the hatches and doors are all closed, perhaps cracking one might help. Hope that helps.
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Old 11-11-2018, 09:36 AM   #3
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Run a dehumidifier so you don't trap all that moisture in... and leave a roof hatch cracked slightly so moisture can escape. I leave my maxfan cap slightly ajar. Read some good boating articles about it...
I have been running mine 24-7 and probably pull a gallon of water a day....
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Old 11-11-2018, 09:51 AM   #4
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Originally Posted by Cdimples67 View Post
Run a dehumidifier so you don't trap all that moisture in... and leave a roof hatch cracked slightly so moisture can escape. I leave my maxfan cap slightly ajar. Read some good boating articles about it...
I have been running mine 24-7 and probably pull a gallon of water a day....
Good advice!

Even after the bus is finished, if you are going to live in it in cold weather, having a dehumidifier on board is a good idea.

I have spent 8+ Winters full time in a bus or RV and found condensation to be enough of an issue that I had to do something.

A small ($99) dehumidifier turned out to be the bomb.

Good luck!
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Old 11-11-2018, 09:54 AM   #5
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Quote:
Originally Posted by CHEESE_WAGON View Post
Just my $0.02. Condensation can be an indicator of leakage, however, more often than not, condensation comes from a major difference between inside and outside temperatures. If your bus has emergency roof hatches, make certain they are tightly closed and sealed. Ditto on the rear emergency door. Check weatherstripping on all hatches and doors. If your bus has auxiliary air-conditioners, there could be drafts getting through them. Still another thought, if the hatches and doors are all closed, perhaps cracking one might help. Hope that helps.
That does help. Thanks. Most of the condensation is around the rear handicap wheelchair lift door. In fact most of my rust was around that area. There are reinforcing bars about 7 inches above the windows that were rusty. I think I will add better seals around the doors in the back.
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Old 11-11-2018, 10:23 AM   #6
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Originally Posted by PNW_Steve View Post
Good advice!

Even after the bus is finished, if you are going to live in it in cold weather, having a dehumidifier on board is a good idea.

I have spent 8+ Winters full time in a bus or RV and found condensation to be enough of an issue that I had to do something.

A small ($99) dehumidifier turned out to be the bomb.

Good luck!
Thanks, I started looking at humidifiers on Amazon. Most of them say they don't work with temperatures less than 50F. How does yours work in the winter if you don’t have heat?
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Old 11-11-2018, 11:02 AM   #7
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Thanks, I started looking at humidifiers on Amazon. Most of them say they don't work with temperatures less than 50F. How does yours work in the winter if you don’t have heat?
I don't work very well below 50F either.......

I have a propane heater that mounts to the top of the 5gallon tank. It DOES contribute to the moisture problem.

Personally, if I get uncomfortably cold the quality and quantity of work falls off.

50F is about as cold as I can manage and still work with my fingers.

Once you are living in the bus I would think that you would have some form of heat?
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Old 11-11-2018, 11:44 AM   #8
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The type of heater you use will make a big difference in the humidity levels. A propane catalytic heater will put out a lot of humidity while a vented RV furnace puts out almost none. Cooking and bathing adds to the humidity level too.



When installing your insulation it's best to seal all the edges with caulk, spray foam or aluminum duct sealing tape (not duct tape) to keep warm humid air from reaching the cold metal skin. You want the humidity to stop at the warmer inside wall where it won't condense.



Bus ribs will act as thermal bridges if you don't insulate over them to make a thermal break between the steel rib and the interior wall covering.



Do a nice careful job and you won't get any mold between the insulation and the outer skin.
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Old 11-11-2018, 12:39 PM   #9
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Any propane appliances that are not vented will add humidity to the interior of the bus.

As will most cooking, showering and breathing.......

Good advice regarding the insulation. Another option, budget allowing, is spray foam insulation. It does a great job of keeping the moist air from reaching the cold metal.
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Old 11-11-2018, 01:01 PM   #10
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Quote:
Originally Posted by PNW_Steve View Post
I don't work very well below 50F either.......

I have a propane heater that mounts to the top of the 5gallon tank. It DOES contribute to the moisture problem.

Personally, if I get uncomfortably cold the quality and quantity of work falls off.

50F is about as cold as I can manage and still work with my fingers.

Once you are living in the bus I would think that you would have some form of heat?
Thanks, yes cold affects me too. I plan to work on the bus this winter when it will be cold. Will look into the propane heater. Saw some at HD today.
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Old 11-11-2018, 01:05 PM   #11
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Quote:
Originally Posted by roach711 View Post
The type of heater you use will make a big difference in the humidity levels. A propane catalytic heater will put out a lot of humidity while a vented RV furnace puts out almost none. Cooking and bathing adds to the humidity level too.



When installing your insulation it's best to seal all the edges with caulk, spray foam or aluminum duct sealing tape (not duct tape) to keep warm humid air from reaching the cold metal skin. You want the humidity to stop at the warmer inside wall where it won't condense.



Bus ribs will act as thermal bridges if you don't insulate over them to make a thermal break between the steel rib and the interior wall covering.



Do a nice careful job and you won't get any mold between the insulation and the outer skin.
Ouch, just returned some of the aluminum tape and traded for duct tape. Guess I need another trip to HD. I was thinking it would conduct the cold.

Has anyone used Tyvek to seal their insulation? I probably could have done this cheaper with spray in foam, but at this point, I have the ceiling three quarters done in the rigid foam. Next bus I guess.
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Old 11-11-2018, 06:36 PM   #12
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I use the Wave 8 heater in my bus with no condensation issues. Besides, I have two windows that refuse to close completely, giving great ventilation.
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Old 11-11-2018, 10:20 PM   #13
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Water vapor will pass through Tyvek but not liquid water. It's used on the outside of buildings as a wind and water barrier but it needs to let vapor through or it would be trapped on the cold side of the wall. On the inside walls it would be best to use plastic film or something non porous as a vapor barrier. If your insulation is closed cell foam the vapor will be blocked from getting to the outside wall.



Spray foam is the high priced option for insulating but is does a really good job.
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Old 11-11-2018, 10:46 PM   #14
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Sprayfoam is the best way to insulate but certainly also the most expensive way.I insulated mine with 1.5" Foamular on the floor with 3/4" DriMax over that 1.5" foamular in the window cavities left after roof raise then 1/2" over all the side walls floor to ceiling 1.5" Foamular on the ceiling.All this over the factory insulation after pulling panels and checking quality and cleanliness of existing materials.In the past week of so we have had below normal temps in the 20's and I have been keeping the bus at 65 with a single 1500 watt electric heater.I am well pleased with the insulation performance. Gene
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