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Old 11-25-2019, 10:46 AM   #1
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Ceiling insulation - stopping the rainstorm

We finished the first trip with our bus, still quite early in the conversion phase. We were in Texas and didn't plan on 22-degree weather, so fired up the Buddy heater. The ceiling was condensing moisture in no time flat. Later that day we put 1" board foam in the ceiling and now only the ribs produce condensation in the cold. We confirmed no condensation behind the board foam. The ribs are just under 1.5", so 2" foam was out since I'm trying to save all possible height, as I'm 6' 2".

As I don't want to lose any more headroom than possible, I'm hoping I can get away with a minimal cover on the ribs to prevent condensation there before installing the ceiling. I've got a pile of sill seal foam, like the following: https://www.amazon.com/Dow-Sill-Seal...dp/B074KK3XGD/ However, I don't know if that's good enough to stop the condensation on the ribs. I'm also considering running 1/4" board foam over everything. Thoughts on whether either of these would be sufficient? We're not living in the bus and don't plan to be in cold climates much, but just need to be able to run the heater on the off chance it gets cold like it did a few weeks ago.

Thanks in advance!
Chris

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Old 11-25-2019, 11:45 AM   #2
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Humidity is a product of the propane combustion, which results in that condensation. If you had a different method of heating your bus (diesel air heater, electric heat, propane with isolated/vented combustion) you wouldn't have that problem.

With the roll material you linked I would be concerned about air still getting to the ribs and condensating behind it.
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Old 11-25-2019, 12:16 PM   #3
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Thanks. That wasn't what I was hoping to hear, but better now than later. I think I'll cover everything with 1/4" board foam, glued to the ribs and existing foam boards. Any gaps can then be filled with canned spray foam, preventing anything from getting behind it.

Seem like a feasible option?

I'd love to get away from propane for heat, but that's probably not in the cards in the short term. I'd love to build a small rocket stove or something similar at some point.

Chris
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Old 11-25-2019, 04:49 PM   #4
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I am assuming the interior sheet metal for the ceiling is not there? so really there was no insulation? Warm air on the cold skin is going to make a lot of condensation. I have two inchs of fiberglass in my ceiling and get very little condensation from my propane heater. Although I do open the roof hatch just a wee bit.

Going to start using an electric heater when I have shore power as well.
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Old 11-26-2019, 07:11 AM   #5
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Originally Posted by farok View Post
Thanks. That wasn't what I was hoping to hear, but better now than later. I think I'll cover everything with 1/4" board foam, glued to the ribs and existing foam boards. Any gaps can then be filled with canned spray foam, preventing anything from getting behind it.

Seem like a feasible option?

I'd love to get away from propane for heat, but that's probably not in the cards in the short term. I'd love to build a small rocket stove or something similar at some point.

Chris
this should work well. The big problem is the cold metal meeting the warm air which is holding moisture (from your breathing and perspiration, cooking, and heating). When that warm air hits the cold metal, condensation ensues.
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Old 11-26-2019, 06:47 PM   #6
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Quote:
Originally Posted by farok View Post
Thanks. That wasn't what I was hoping to hear... I think I'll cover everything with 1/4" foam board, glued to the ribs and existing foam boards. Any gaps can then be filled with canned spray foam, preventing anything from getting behind it.

Seem like a feasible option?

Chris

Brokedown is partially right, catalytic propane heaters (is this the style you have?) are known for promoting humidity and/or condensation. But condensation can/will happen with or without a catalytic heater, the human body is another primary contributor to humidity in a small enclosed space, and the air naturally has some amount of water in it (humidity). This is why even in a ten with no heat source, condensation still forms overnight in cold conditions.



Condensation is the product of the difference in temperature between the inside air temperature and the temperature of a surface (exterior walls in this case), and the humidity of the air. Air's capacity to hold moisture diminishes as it gets colder (this is known as the 'dew point') and the temperature difference inside and outside tents to become more pronounced in colder weather which is why condensation is much more of a problem in cold weather. Humid air will 'condense' on a colder surface pulling water vapor out of the air and turning it to liquid water on the cold surface.



I see two major ways to address this problem, find ways to minimize the humidity of the interior air (crossventilation, choosing a heater that doesn't contribute to humidity or ideally pulls humidity out of the air), or find ways to minimize the difference in temperature between the inside of your exterior walls and the interior air (insulate! with a closed cell insulation). I don't know if 1/4 foam will be enough to do the job but its certainly a step in the right direction and should be a helluva lot better than nothing.


Let us know how it work out for you!
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