Skylight Airleak?

[Joel Ashley]

Last fall I noticed vapor between the inside and outside clear panels of our shower skylight.  This winter, the cooler weather meant the accumulated vapor condensed out and settled in a downhill corner of the skylight, visible as a pool of about a quarter cup of water.  

As far as I could tell last fall, there was no obvious leak in the skylight's roof sealant, but obviously humid air got in between the panels, even if water did not.  It may have entered from a breach inside, but I haven't tried taking the inside moulding off yet to examine things.  At Bend in 2008, I asked the tech to check the skylight because I'd noticed (seen from the inside) a black defect along one edge, an apparent slight abberation of installation sealant.  He found no problem, but couldn't have actually examined the black stuff because of the white outer sealant.  I doubt he checked from inside.

My question to those who might know is, how is the skylight constructed?  I'm concerned that driving the coach might instigate movement of that water into the roof laminations, where it could do some damage eventually.  Or would the water, due to the assembly character of the skylight's inner and outer panels, be unlikely to get out from in between them?

My first inclination is to drill a 1/8" drain hole in the low corner of the inner panel and let the water out.  Then on a 30% Relative Humidity day, seal the small hole with silicone.  But that doesn't resolve the initial breach, wherever it is.  Any experienced opinions are welcome, as I can only guess how these skylights are built, and how air is getting between the panels, which I'd think were heat and/or chemically sealed/fused at the factory in a dry low RH environment.  But I dunno.

Thanks,
Joel

Note in the photo below, that today's sunny day has caused the pool to partially evaporate and put condensate on the inside of both panels.

[LEAH DRAPER]

HI Joel
Nothing to offer regarding the skylight construction, But is that "black spotty stuff mold in addition to your sater problem.  If so, that might not be a healthy situation either.  Just saying.......

Leah

[Edward Buker]

Joel,

 With a heat gun you should be able to carefully heat the sealant, remove the bulk of it with a putty knife, and work the skylight up. My first choice would be to unfasten the skylight and pull it and then examine why it is leaking. After doing all that work, if a new one was available, I would opt to install a new one knowing these Plexiglass skylights deteriorate with age and sun exposure. I do not know how they are constructed but it would make sense that the two layers of Plexiglass are either heated and sealed together or adhesive sealed and bonded to each other. Obviously water between the Plexiglass layers is a fail of that seal and the roof sealant lapped over it.

I would consider drilling a small hole in the underlying panel as you describe as a second choice but I would reseal the the roof Plexiglass joint by overlapping it from the top with an appropriate sealant first. Acrilar or 3M 5200 sealant. Beaver Coach Sales could provide you with the best choice that they use. I have a skylight in my home that is rated for hurricanes. It is constructed with a high strength thermal pane panel on top and then spaced approximately 1/2 inch below is a Plexiglass panel and in the lower corner they have drilled a small hole as part of their normal construction technique. They vent between the panels and I have not observed any condensation issues. I'm not sure if that would eliminate all your condensation between the panels but there is at least an example of a vent hole in Plexiglass as a normal construction technique. Hope this helps.

Later Ed

[Gerald Farris]

Joel,
The skylight is installed on top of the roof. The hole is cut in the roof, and the skylight is secured to the roof with screws. Since the skylight is about 3 or 4 inches larger than the hole that was cut into the roof there is no chance that water will get into the fiberglass roof unless it is leaking down one of the attaching screws. If water gets to the edge of the opening in the roof, it will leak into the interior of the coach.

The interior layer of the skylight is clear and the exterior layer is is tinted to prevent heat build-up between the two layers. A few coaches have a small hole in the inner layer to allow for air movement in and out of the space between the two layers, but most skylights just depend on the flexibility of the plastic material to compensate for the difference in pressure from heat and altitude changes.

The bottom line is that if you have a quarter of a cup of water between the layers of your skylight, it is either cracked or the sealer around the edges is leaking. When the skylight was installed, it had an automotive grade putty laid on the roof and the skylight was screwed down on top of it. Then a flow grade automotive sealant was used to seal all of the screws and the edge where the upper and lower layers  meet all of the way around the skylight, and that is where your leak is if it is not cracked.

This description only pertains to later model coaches were the skylight is mounted flat to the roof. On the early model coaches like the 1993 Patriot that I use to own, the skylight is curb mounted on a raised structure about 4 or 5 inches above the roof and has a metal retainer all of the way the edge holding it down.      

Gerald

[Jeremy Parrett]

the skylight is constructed of two thin payers of plexiglass. They are about 1/2 apart at the dome and sealed together around the lip/flange where the unit is screwed to the roof. The outer layer on my 2000 Marquis cracked with age. I had water in the corners same as you have.  Replacement uints are available. If you call Lazydays in Flroida they can head you in the right direction.

[Tom and Pam Brown]

Joel,

just replaced mine on the 99 Marquis.  Not too much trouble except getting the old sealant off of the outside.

Mine was old and spider webbed as yours appears.  Took about 2 hours and i ordered one from Beaver/Monaco and was shipped to me for about $200.  The new one makes a big difference.  As Gerald and others have stated there is no way for the skylight to leak under normal conditions there is approx 33 screws holding it down.  If you would like i can tell you how i replaced mine.

Good luck

[Gerald Farris]

Joel,
I replaced the skylight on my 2000 Marquis last summer when I was in Bend because of hail damage. Beaver Coach Sales had it in stock, and it was about $100.

Gerald

[Joel Ashley]

Thanks Guys.

Leah, the spotty-looking stuff is just water droplets that have condensed out and perhaps look dark against the sky;  there is no mold.

The coach has been parked on our pad for over 2 years, and this problem didn't appear until last summer and fall.  I checked the roof seals and can find no problems, nor does the outer dark panel appear deteriorated or cracked in any way.  I'm pretty sure the moisture didn't get between the panels via liquid water, but rather by humid air.  Like the telltale fog on our entry door window, I began noticing a slight fog on the skylight last year, but did not assume at first that it was between the panels.  Then in time I noticed the fogging had increased and was coalescing into droplets in places, and closer examination proved it was between panels.  It got worse by late fall, and during the cold winter, it all condensed into a pool at the low end.  With Spring sunshine, the pool is beginning to re-evaporate as in the photo.

Having dealt with dry rot in the roof of a previous coach, I am paranoid about moisture breaking the roof barrier anywhere, thus my concern about the skylight's ability to hold that water inside itself.  I'll probably go over the outside with a fine-toothed comb to be sure, and remove the inside skylight ceiling moulding to check for a hidden breach or crack there that could be siliconed over.  But any humid air left inside will fog in the summer, and getting existing moisture totally out before resealing ... well, I'll need genius or good luck for that, and I'm not even 50/50 on that!  

Last summer in the Northwest was one of the wettest on record, but I still didn't think I needed to run an air dryer and dessicants inside Monty Rae like I do in the winter.  I suspect unusually humid air infiltrated the skylight from the inside then, and slowly built up over time.  Barring a found breach, I may try a drain hole or two, but if fogging continues, I'll replace it;  sounds like the work removing/replacing it and two kinds of sealants is more costly than a new unit itself.

-Joel

[Gerald Farris]

It has been brought to my attention that a post earlier on this thread that stated to use 3M 5200 as a sealer to overlay existing seam sealer was being confused with a sealer to install a new skylight.

3M 5200 is a polyurethane structural adhesive and sealer that was primarily developed for the marine industry. It is a great product, however since it is a structural adhesive it should never be used to install a part like a skylight that will very possibility need to be removed in the future. Removal of a part that was installed with a structural adhesive will probably damage the part and the fiberglass wall or roof that it was installed on.

Gerald

[Gerald Farris]

Joel,
If your skylight does not have a vent hole drilled in the inner layer, and most units do not, there is no way for air to inner the void in-between the two layers unless it is entering through the the seam on the roof or a crack and it is a water leak also. So you need to concentrate on a water leak not a benign air leak from the interior of the coach.

Gerald

[Joel Ashley]

Thanks Gerald.  Today and tomorrow are the first really solidly sunny days this winter, so I'll take advantage of it to get out and carefully go over the entire skylight once again.  

-Joel

[Edward Buker]

Very good point on the 3M 5200. I have used it on boats to bed fittings and I have removed the fittings later with no damage to the fitting or the fiberglass. However, I would not want to attempt to remove a plexiglass skylight that had been bedded in 3M 5200. Thanks for catching this oversight.

Later Ed

[Joel Ashley]

Tom and Jeremy-

Mine isn't spider-webbed or obviously damaged, nor is the surrounding sealant apparently compromised anywhere.  That is part of my frustration;  the unit looks nearly new.  Any apparent fault you see in the photo is only condensation on the inside of the outer layer, due to warmer temperatures lately causing the pool of water to evaporate.

-Joel :-/

[Edward Buker]

Joel,

Having owned boats and motorhomes over the years, one thing is clear, when it comes to leak sources they can be very difficult to source as you can see. A visual inspection can detect only what is obvious. The interface between the sealant and the fiberglass or the sealant and the Plexiglas may be imperfect due to age, expansion and contraction, or improper surface prep at the factory leaving something like mold release agent on the surface. Water can weep into the interface and you would never know. The amount of water that you have between the panels looks like it exceeds what one would expect from condensation. If the skylight was constructed and sealed properly there would be no path for condensation to ever get in.

 If you choose to drill and drain I would clean the old sealer, Plexiglas perimeter with Windex first. Then I would clean the edges of the fiberglass out and inch or so from the old sealant edge with an automotive wax and grease remover (PPG DX330 is very good). Then I would use whatever sealer Beaver Coach Sales recommends to cover and lap over the old sealant to extend the sealed edges out onto the freshly cleaned surfaces. This seals the old sealant edges and interfaces. If the skylight looks new and has no cracks this may get you where you need to go with limited expense and work. If not then you know you need to change it out. Hope this helps.

later Ed