Moisture From Condensation?

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Moisture From Condensation?

Postby Tomterrific » Fri Apr 17, 2020 7:07 am

Here's a tough one. I used Revolution ply on both the inside and outside, ceiling and roof, with 3/4 inch Styrofoam insulation between. I did not completely fill the edges around the foam but PL was used to seal each cross rib and edge of the ply. Somehow the outside ply got enough moisture to get soft. The inside shows no damage. Where did the moisture come from? I have a weird idea.

Tt
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Re: Moisture From Condensation?

Postby tony.latham » Sun Apr 19, 2020 9:45 am

Somehow the outside ply got enough moisture to get soft.


Photos?

What is the exterior sealed and covered with?

:thinking:

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Re: Moisture From Condensation?

Postby Tomterrific » Sun Apr 19, 2020 11:36 am

The photo will not show damage. The front is covered with aluminum foil faced butyl flashing. The damage was first noticed years ago when I saw small paint bubbles. The paint and primer is oil based. The paint was scraped and another coat of Rustoleum white was added to the front. Eventually I added the flashing. I noticed soft spots under the flashing this spring.

I'll give my thoughts as Tony seems interested. I have a hobby with old motorcycles. Gas tank rust is a problem. The tank breathes through the vent with a change in temperature. Ohio is a wet state with daily temperature fluctuations. These motorcycle tanks can capture surprising moisture over one winter let alone several years of sitting. My camper sits outside and I believe the air space, although small, has captured enough moisture to wet the lower cheap Styrofoam leading to the soft spots.

My suggestion to future builders is:
Use extruded insulation board, not the expanded Styrofoam like I did. I found boat building sites saying the expanded foam will hold water.
Do not leave any air space between the roof and ceiling to trap moisture from breathing due to temperature change.
Place vents inside at each of the lower spaces so moisture can escape. Something I should have done when I first noticed this.

I still don't know why I have this problem. The flashing has the face of the ply absolutely water tight.

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Re: Moisture From Condensation?

Postby tony.latham » Sun Apr 19, 2020 11:57 am

The photo will not show damage.


Does the roof sit on top of the walls or is it joined between the walls?

:thinking:

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Re: Moisture From Condensation?

Postby RJ Howell » Sun Apr 19, 2020 1:47 pm

My only thoughts here come from my Home building years and the phase we went through of plastic sheeting on the inside of the wall and Tyvek on the outer. What a mess of moisture trapping!

Sounds something the same to me... trapped with no outlet. Did you seal both sides? I am a huge fan of sealing the exterior tight and letting the interior breathe.
Also the air space you mention bothers me.. I think you have hit on an issue.

Do hope you can work through this and something good (dry) comes of it.
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Re: Moisture From Condensation?

Postby Tomterrific » Mon Apr 20, 2020 8:31 am

The roof is on top of the walls with ribs going across attached to the walls. The ceiling is inside the walls. The crappy insulation is sandwiched between the roof and ceiling. I believe this is conventional teardrop construction. The walls have no insulation. The edges are sealed around both the ceiling and roof. I believe RJ Howell has the correct idea. Too much seal with no escape.

My camper has sat outside both winter and summer since I built it some years ago. I'm sad to see it deteriorate so but I guess I it is not unexpected. It's fixable but I would like a 5 foot bed. Hmmm....?
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Re: Moisture From Condensation?

Postby Pmullen503 » Mon Apr 20, 2020 9:33 am

Just a note: Revolution ply is crap.

I had that around the door frames on my foamy and it delaminated after a few years. I had to rout it out and replace it with marine plywood then recanvas.

I know it supposedly rated for tile underlayment but throw a piece in a bucket of water for a few days and see what happens. Better to use a true exterior rated plywood or marine ply if you never want to worry about it again.
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