So first I want to correct something I said yesterday. Tyvek tape is NOT a vapor barrier tape - it is an air infiltration product, as is Tyvek house wrap. I think.
The aluminum tape is likely a vapor barrier (it's metal after all - right?), as is the foil-faced feature of both the poly-cyan board and Reflectix. What makes it vapor barrier also makes it good to seal out drafts, I THINK that's why AnEv says he might have used it himself - you know, a more effective sealing of all undesirables. Please correct me if I'm wrong.
Like I said, I considered the aluminum tape and that's one of the reasons I primed the outer surface of the wood framing, to have a cleaner, better surface for the tape to stick to.
But what I didn't want to do is make it so tight, with so few paths, that any water vapor that gets into the wall condenses on the colder surfaces of say, the Reflectix or the silvery aluminum side of the poly-cyan board and become trapped against bare wood in liquid form. I felt that could be mitigated by even priming the back of the exposed paneling, but then condensed water just runs under the framing to the un-primed paneling and creates the water problem there. And I felt the tedious priming of little squares of "paneling backside" all over the camper might LOOK pretty in photos, but wouldn't help in such other issues.
So I thought what about house wrap tape - Tyvek style. Tyvek is an air-infiltration product - reduce drafts, and is fairly effective for water resistance in liquid form, but is breathable for water vapor transmission, think Goretex. There again, might its use reduce condensed (liquid) water coming OUT, if and when it gets inside?
And do I need to additionally control drafts? Or is the tape an unnecessary, perhaps undesirable step? My drafts are controlled quite well I think by excellent fit construction, new and re-use of rubber/vinyl gimp, and interior joint caulking. Drafts should also be reduced through the effective exterior sealing of openings and siding edges through the use of butyl tape, which of course has the main purpose of keeping exterior liquid water at bay.
And then there's the aluminum siding which acts as a pretty large surface for resisting both drafts and passage of water vapor from inside to out (in addition to its excellent property of keeping exterior liquid water out). But the cold inward surface of the metal is a great place for interior water vapor to condense against! Wherever that rests against wood is a "mold and rot" just waiting to happen, not to mention an aluminum corrosion issue (Internet research - aluminum against bare wood). :/ <-Consternation face.
That's one of the main reasons I chose to place Reflectix over the roof prior to siding (in spite of it slightly increasing circumference and potentially affecting the fit of the siding) and in choosing to prime the exterior surface of the exposed framing members.
But then I found this article
Vapor Barrier Primer versus the Poly-Ethylene Cult.In essence these points.
-Poly Ethylene vapor barrier is 60 times more effective than the Canadian building requirements. A simple Vapor Barrier Primer is TWICE as effective as the requirements.
-Poly barrier can TRAP moisture on the WRONG side, at best - reducing effectiveness of insulation, at worst - creating "water in your walls" problems (mold, rot, etc.)
-Best building practices (and regulations) should take into account differing environments and climates - one size does NOT fit all.
-Water vapor coming into the wall though air-infiltration is HUGELY greater than diffusion (moving THROUGH building materials such as sheetrock, wood, etc.). So controlling drafts is king, but perhaps not at the expense of placing a condensing trap layer?
So I was more uncertain than ever on what to do. But the article also points out the simple fact that water vapor becoming liquid in your wall (condensation) is associated with warm, moist air moving toward cold, dry air. We all know that, we just need a reminder on occasion.
In Lil' Queeny, I'm controlling drafts through: tight construction, ample use of caulking and gimp and exterior sealants, and controlling diffusion through three layers of polyurethane finish on probably every interior wood surface.
Secondly, without an air-conditioner, it is terribly unlikely we'll ever see warm, moist air moving from outside in, (drafts or diffusion) condensing on a COLD interior surface.
We are MOST likely to see warm, moist interior air (winter camping - which will likely be reduced every year exponentially) moving outward, BUT with use of a catalytic heater we MUST have slight ventilation ANYWAY, thereby reducing any chance of water in the walls, especially because of our paint-on vapor barrier (three coats of polyurethane).
And over-reaching ALL of THAT! We live and camp in a desert. :)
Wyoming is pretty dry (speaking of humidity). During storage, there is little chance of significant humidity and temperature differentials inside to out. During use, ventilation will be in play one way or another.
I "done" what I think is right for our circumstances, your mileage may vary. So no tape - now get outta my head. :)
P.S. Photobucket is down this morning. And you know what they say, 1000 words beats a picture.
