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Old 01-25-2010, 12:21 PM   #1
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In-Shell Condensation?

I am in the process of installing a solar system on my 2008 25 FB.

I drilled a hole through the roof in order to run an 8 AWG wire through to my Solar controller located in the upper pantry cupboard. (I'll post pictures when I'm finished)

When I put my finger into the fresh hole in the roof, I can feel damp insulation there.

I store the unit outside and it has been a very wet winter but I do not have any visible leaks inside the unit (since repairing the latest leak around the bedroom window that is ...) The interior has no condensation visible on windows etc. Feeling around inside the walls reveals no moisture that I can feel.

The day when I drilled into the roof was relatively quite a bit warmer than it has been and I have been running a small electric space heater in the unit while I work so there may have been more temperature shifts than than the typical storage day would have, but I am dismayed to think that there is moisture inside the shell.

Is this likely from an occult leak or is it possible that this is due to condensation inside the outer skin but inside the shell? A modern domestic home will have vents in the roof to prevent the build up of condensation inside the attic, wouldn't it make sense that the A/S should have some equivalent means to ventilate the interior of the shell?

Any thoughts? I am still on warranty but I have the impression that A/S doesn't consider leaks to be their responsibility and design flaws don't get remedied either.


Should I be ventilating the shell somehow or just look harder for an occult leak?


Any thoughts would be appreciated.

-evan
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Old 01-25-2010, 01:06 PM   #2
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DW found wet dripping cans, all the mirrors fogged, and it wasn't raining, when we get a shift in temp anything colder than air temp gets wet, including cement in carport and patio. My solution was to put a boat dehumidifier(equivalent to a light bulb) on a timer for 4 hrs each morning, no more condensation. Your weather might be similar to ours in that you probably have 80-90 percent humidity days.
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Old 01-25-2010, 02:01 PM   #3
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Thanks DaveFL but I do have dehumidifiers in the interior (2 passive dessicant types). I have no evidence of moisture in the living areas, it is inside the shell at the roof level that I feel the damp insulation. Thus my question. If I hadn't drilled the hole, I'd have had no idea that that moisture was there.

-evan
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Old 01-25-2010, 02:19 PM   #4
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Lots of discussions in various places about this topic... condensation happens.... when hubby did a shell off on our Bambi he tried to think about this... not sure we came up with any definite answers. We used to have a sailboat and they have open airways between in the inner and outer walls along with a bilge... the air vents could be opened so when under power (wind or sail) the air would flow through and dry out the moisture... often wondered if some sort of cowl vents would be good for an airstream. Sure this has been answered. Best thing, keep it as dry as possible... and check all seams on a yearly basis. Go camping, wear the trailer out!
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Old 01-25-2010, 06:38 PM   #5
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Quote:
Originally Posted by CaddyGrn View Post
Lots of discussions in various places about this topic... condensation happens.... when hubby did a shell off on our Bambi he tried to think about this... not sure we came up with any definite answers. We used to have a sailboat and they have open airways between in the inner and outer walls along with a bilge... the air vents could be opened so when under power (wind or sail) the air would flow through and dry out the moisture... often wondered if some sort of cowl vents would be good for an airstream. Sure this has been answered. Best thing, keep it as dry as possible... and check all seams on a yearly basis. Go camping, wear the trailer out!
Thanks Caddy. I do hope to wear out our A/S from frequent use rather than storage rot. I am a little leery of the idea of cowls etc if they allow too much water in instead of out.

I've been searching various keywords to see if any other folks have tackled this issue & I haven't found anything definitive.

I'm wondering whether a powered ventilator at the top of the roof ventilating the space between skins with small grommeted holes at floor level from the interior to the between skin interspace might allow for some effective ventilation of this area?

I was thinking that one could use a modified plumbing vent or something like this Lil' Stanker vent to do the job.
Lil' Stanker™ MK-IV Deodorizer Fans

Alternatively. One could open up the interior skin in a few places near the ceiling to allow egress of any saturated air but it might also allow too much of the humidified living space air into the skin space.

Any other ideas are welcome

-evan
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Old 01-26-2010, 02:07 PM   #6
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When you see this on the outside, do you ever wonder what's going on inside the skin?


Maybe I'm unnecessarily concerned but I'm thinking it would be good to ventilate the space between those surfaces.

-evan
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Old 01-26-2010, 03:01 PM   #7
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The light bulb idea works great. I use the same thing in my Safari.
The dessicant will get saturated and then give off moisture, so it needs replacement often. I wouldn't try to ventilate the walls. The interior skin allows air travel, as it's not sealed at the seams like the exterior skin, so venting the interior of the trailer(fantastic fan) will have the same result as venting the exterior skin, without the possibility of water infiltration.
I reinsulated with Prodex and now I no longer have a sponge inside of my walls, but the condensation still happens.

Rich the Viking
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Old 01-26-2010, 05:45 PM   #8
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Moisture control in the cold

Hello Evan. Consider the human exhalation condensation you see on the windows & Vista Views in the morning if all are closed overnight. Even when I'm camping in -10 °C conditions (mid-teens °F), I leave a window ajar at the other end of the Safari to let respiratory moisture escape. If I'm not parked at a bit of an angle I'll open one window and turn the latch 90° to force it ajar. I tend not to use ceiling vents due to rain risk -- and the Fantastic Fan opens way more than necessary.

In cool conditions we do travel with sleeping bags so that I can sleep with the furnace not running full-time; I usually set it to hold temperature at maybe 12-13°C (mid-50s °F) ... or a tad lower.

I do agree with VIKING's post that the interior skin allows moisture travel outward to condense as it approaches the outer skin. In my experience, DampRid just will not keep up with active habitation generation of humidity. Breathing is a bigger factor IMO than cooking -- but both will aggravate the problem.

Modifying factors: I do store under a roof. I use DampRid in storage but that's about all I can expect of it. IMO no single leak could produce as generalized a problem as intra-shell humidity.

Many other threads on the topic; but a couple....
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Old 01-26-2010, 10:37 PM   #9
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Thanks CanoeStream & Viking,

I have used many of these same methods to cut down on humidity when we are using the A/S. I do not have access to 120V power where I store the unit so have had to use the dessicant stuff as a precaution. (The light bulb trick would be fine if I had power.) In actual fact though, despite the outside location & even a small leak that I caught early near the front curbside BR window last month, I have not seen any condensation inside the unit when I check it or when I had brought it home. The glass is clear & it smells fine inside without any hint of mildew etc. So far, we have had no problem keeping the unit from steaming up inside when we're in it. (vents open, proper heat adjustments etc.)

This is why I was quite perturbed to feel how damp the insulation was in that area of the roof that I could feel. ( I suppose it is still a possiblilty that there is some water penetrating the shell through a leaking plumbing vent or something; I will have to do the pressure/bubble test in the next month or so. )

What seems to be the common theme with all your responses so far (if I am reading this right) is that there really is no true vapor barrier between the interior living space and the inside surface of the outer shell; therefore, keeping the interior properly ventilated should keep the airspace between the shells free of excess moisture.

The puzzle for me in this is that the interior seems dry, I leave some vents open to keep the unit aerated but the insulation in the ceiling / roof space is damp. I will have solar panels & some power to run low draw ventilation fans in the next month but don't think I can provide any heat like a light bulb etc.

No-one else seems to think that a separate ventilation strategy for the exterior shell airspace should be necessary... I'm still scratching my head over all this.

If anyone else has access to their ceiling, can you tell me whether your ceiling insulation is damp?

Thanks for all the feedback. I appreciate it.

I think I'm going to look harder for another leak.

-evan
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Old 01-27-2010, 04:45 AM   #10
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Hi Evan;
Perhaps being the one to try and change Nature's way is not a easy thing. What occurs inside your walls is a part of natural process associated with temperature differentials. At any given circumstance when temperatures differ considerably on each side of a higly temperature transmittable barrier such as aluminum sheeting, the condensation will form. It is a natural occurence and venting your space inside the walls is as impossible as stopping this condensation by any other means than reccomended by others on this thread. The rib structure inside your walls forms a multitude of barriers for any air movement. Even if you installed a fan driven vent you cannot move enough air inside your walls to make any real difference.

I have restored a 1973 26" Argosy by insulating it with Reflectix [bubble foil]. Each pannel had a 1/2" thick Clegicell foam strips glued to outer skin with 3M 5200 adhesive to attach and support the foil. This offered 1/2" airspace between outer skin and foil. Foil was precut oversize and formed along the cross section of the ribs and it was glued in. After adhesive has dried, foil was trimmed to 1/8" past the rib so that inner skin could compress the cross section of the foil. This method minimized the temp transfer area. Some condensation still occurs in the 1/2" airspace on the outside of the foil but it is minimal.
The foil acts also as moisture barrier unlike fiberglass insulation which permitts cold or hot outside temps to colide by means of air transfer. Since you are not going to undertake such serious modifications you can only resort to venting the interior and keep temps inside and outside close as possible to eaqual. During storage period do not heat the interior and keep vents slightly open and store it under roof to keep the sun off the trailer. While there are many contradicting opinions on forums in reference to insulating, bubble foil offers better temp and air transfer barrier. Thanks "Boatdoc"
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Old 01-29-2010, 04:23 PM   #11
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Quote:
Originally Posted by boatdoc View Post
Hi Evan;
Perhaps being the one to try and change Nature's way is not a easy thing. What occurs inside your walls is a part of natural process associated with temperature differentials. At any given circumstance when temperatures differ considerably on each side of a higly temperature transmittable barrier such as aluminum sheeting, the condensation will form. It is a natural occurence and venting your space inside the walls is as impossible as stopping this condensation by any other means than reccomended by others on this thread. The rib structure inside your walls forms a multitude of barriers for any air movement. Even if you installed a fan driven vent you cannot move enough air inside your walls to make any real difference.
Thanks Boatdoc. I think I have a fair appreciation for the physics here but the lack of vapor barrier & yet the ability of the insulation to trap moisture in the walls & ceiling is a problem. I wondered whether there were any holes in the ribs to allow movement of air but perhaps not....hmmm . My fan idea may not be viable.


Quote:
I have restored a 1973 26" Argosy by insulating it with Reflectix [bubble foil]. Each pannel had a 1/2" thick Clegicell foam strips glued to outer skin with 3M 5200 adhesive to attach and support the foil. This offered 1/2" airspace between outer skin and foil. Foil was precut oversize and formed along the cross section of the ribs and it was glued in. After adhesive has dried, foil was trimmed to 1/8" past the rib so that inner skin could compress the cross section of the foil. This method minimized the temp transfer area. Some condensation still occurs in the 1/2" airspace on the outside of the foil but it is minimal.
I have a feeling that since the unit was not really in use & still had damp insulation, that the most likely explanation is not really condensation but a leak. The caulk around the plumbing vents is already looking pretty rough & cracked in places.


Quote:
During storage period do not heat the interior and keep vents slightly open and store it under roof to keep the sun off the trailer.
I am investigating the possibility of storing the unit under a cover. This might help reduce the UV damage & also keep the moisture out. Covered storage is pretty hard to come by around here though - it it ain't cheap.

-evan
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