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Old 02-22-2021, 05:36 PM   #1
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Join Date: Oct 2015
Location: Cookeville TN
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Metal Studs and Condensation

Hey all, curious what you know about metal studs and condensation?

I had originally planned to just screw through a layer of insulation directly into the metal ribs in my box truck, but members in another group made the point that this would cause condensation and water damage over a few years.

So what's the best alternative: Do I cut a bunch of wooden 1x1 studs, cut away some insulation I've already installed, install those on the ribs and screw to those?
OR, not backtrack and save material by using plastic expanding sleeves in the metal ribs so the screw and rib don't actually touch?

Or do something else? Any advice welcome, seems important and has been a hang up for me
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Old 02-22-2021, 09:51 PM   #2
Skoolie
 
Join Date: Apr 2020
Location: Northern California (Sacramento)
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Year: 1999
Chassis: Ford E450
Can you give us a better description of the wall system? I can't tell from the picture what the screws are holding. Is it the metal studs?

Lots of posting around the topic of condensation, so some searching in this forum will give you a bit of background on basics. Short lesson, you want to have a little metal-to-metal contact between the inside of your bus or truck(warm and humid) and the outside (cold). It's the cooling of the inside of the bus from conductance that causes condensation to form on the interior metal surfaces.

Screws are a pretty small surface; but having said that I used to live in the colder part of the country and remember seeing condensation on the heads of nails driven into lumber in direct contact with the outside air.

And without really understanding your wall construction I'm not sure if cutting away insulation will net you anything. It will certainly reduce overall R value.

The real culprit in condensation is propane heating, which pumps a lot of moisture in the air. Limiting humidity inside is equally a factor in overall vehicle health over time.
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Old 02-23-2021, 01:16 AM   #3
Skoolie
 
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Join Date: Aug 2019
Location: Auburn, WA
Posts: 146
Year: 2000
Coachwork: IC / Amtran
Chassis: 3000 / 33' Flat Nose
Engine: IC T444E / Allison MT643
Rated Cap: 72 Kids / 48 Adults
I'm in Seattle area. While not super cold in general, it is super wet!

I have used screws into the metal ribs, but then I covered them with silicone to break the thermal bridging effect.

My main problem has been the actual interior of the roof skin and the curved roof ribs.

I'm not seeing issues with my vertical ribs/skin or much even on my windows.

I'm using rigid foam, then I screwed wood stringers with thin foam between the stringers and ribs. I didn't see one screw condense, but boy the ribs and skin sure did!

One thing that may be part of the problem is I put the aluminum side of the rigid foam against the skin. I'm going to flip that. The next is that the rigid foam doesn't really conform to the skin and leaves gaps between the skin/ribs an the insulation. So, I'm thinking of putting wool insulation as a backing to the rigid and stuffing it in the gaps around the ribs and rigid.

That fills the cavities made by the rib grid, but it still leaves the bottom of the ribs exposed. I'm not sure how I'm going to cover all of that.

If I wasn't as far along with my interior build and had the money, I'd spray foam. Hindsight.

I think (hope, pray, beg the bus gods) that once I cover all the ribs and put up the ceiling it will create a good thermal bridge.

I plan on using some kind of dehumidifying.

I'm also hoping that when I paint the roof with elastoseal that it provides even more of a thermal break.

Oh, per the Reflectix insulation, the company states that it needs 3/4" air space between it and any metal to avoid thermal bridging.

Hope this helps.
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Old 02-23-2021, 08:47 AM   #4
Skoolie
 
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So firstly it always important to research and understand what condensation is and most important, to fully understand what causes it, and why. Then you will have a grasp of how to reduce or prevent it.


Think about an ice cold beverage in a glass on a hot day. The outside of the glass starts to experience water running down the outside. How can this happen? The glass is not porous. How about a cup of hot coffee on a cold morning? The outside of that cup does not sweat or condensate. But a column of "steam" will rise so long as the coffee remains hot. Why? Now just draw a glass of tap water. Nothing? The glass does not sweat or condensate, and no steam column. Why? Temperature differential? Temperature equilibrium?



Lots of answers and explanations through a google search, and even more on youtube.
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