Jfet wrote:
sabconsulting wrote:
Just to add to bka0721's comments - this is the write-up I did on adding solar panels to my aluminum roof:
Solar clicky...
The first page also contains links to the complete roof rebuild.
Unfortunately I have lots of screws going through my roof, but I didn't have much alternative if I wanted to keep all the hatches etc. that the camper originally had.
Cheers,
Steve.
Steve, very nice job on your aluminum roof. I am now unsure if I want to go aluminum though. I see you used a vapor barrier under the aluminum (smart) but this would not allow me to sikaflex the aluminum directly to the marine plywood. Perhaps TPO or that other EPDM? stuff would be the better way to go for me, so I can bond it to the plywood that is screwed/glued to the metal roof joists.
Hmmm...
Having not read all this, I'm not sure of the application here, but I would not ordinarily recommend thee sole
"vapor barrier under the aluminum". For one thing, the aluminum is a terrific vapor barrier all on it's own.
The most important other aspect, though, is that the aluminum already forms a vapor barrier on the exterior "cold side" where we don't really want it. Because of the need for "wet" water-proofing, it can't be helped, but this aluminum barrier traps any attic cavity humidity from properly dissipating outdoors through the outer membrane. That is to say that any vapor that penetrates the inner ceiling cannot continue to the outside which, in turn, means that it is likely to be trapped and reach the dew point within the wall cavity and therefore condense to "wet" water. Rot and mold can follow.
As an example, a full size stick home has a large hollow "trussed" attic that is ventilated to allow vapor escape, even though the shingles prevent rain intrusion. Some curved camper roofs also have shallow trusses that allow venting, wiring and even A/C ducts to run the length of the RV roof.
It is possible to vent a
flat camper ceiling in a similar way by running an additional layer of purlins (cross-timbers) under rafters at a 90 degree angle. After the ceiling panels are attached, air may still freely circulate through the
entire matrix by weaving around the perpendicular framing, if that makes sense. A bonus is that wiring may be simply threaded through this same matrix without drilling holes in single layer roof joists. The idea would be to add insulation
only between the purlins and allow open ventable air space above this layer. It is
important to add a "warm side" vapor barrier between the ceiling panels and bottom of the insulation. This is actually more important on a roof assembly than wall assembly. There is a tendency of more accumulated vapor towards the ceiling.
TRIVIA:
The breathable air inside the cabin is made up of mostly nitrogen and oxygen in that order of prominence. Both these gaseous molecules exist in relatively dense pairs, O2 and N2. Because they exist in pairs they (the denser air) are actually heavier than H2O "gaseous" dry vapor which exists as "feathery" single molecules. H2O is only one "half-heavy" oxygen molecule and two very light hydrogen atoms. Dry water vapor therefore "floats" to the top of the interior atmosphere, just like light wood on heavy water. This also true of outdoors evaporating humidity. Outside the
invisible rising vapor eventually reaches a cool upper air that is cold enough to condense the vapor to tiny droplets, combined molecules ("wet" water) we are able to see as clouds (same as fog). If the droplets coagulate too much, they get compact and heavy enough to fall as rain. The point being, water vapor itself, is lighter than air and collects near ceilings.
Wes
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