Jfet wrote:
ticki2 wrote:
There would be no need for a vapor barrier between the aluminum and plywood , the aluminum , especially if one sheet , is in effect a vapor barrier . Add to this that is the wrong placement of a vapor barrier which should be on the inside wall ( warm side of insulation ) it becomes a negative . On a TC which usually has an impervious material as an outside skin I question if a vapor barrier should be used at all , even on the inside . Some how the wall has to breath or condensation will be trapped and eventually cause problems . Unless of course you can vacuum seal it or fill it with gas as in thermal windows , but I doubt that is practical .
ticki2, but then why did he put the vapor barrier right under the aluminum and nobody on the 11 page roof rebuild thread said anything negative about it?
In that thread he mentions putting the plastic under the aluminum as a precaution against condensation under the aluminum , not exactly a vapor barrier . I humbly submit that Tyvek would have been a better product for that purpose . The same problem of condensation in that situation will exist whether the material is aluminum , steel , glass ,plastic , or rubber . It's a non-porous material trapping moisture . In a S&B building moisture can escape through the exterior of the wall and roof , in an RV it cannot , that is why I question the benefit of an interior vapor barrier in an RV . I don't pretend to be an expert in RV building , or anything else for that matter , just food for thought .
I have used Tyvek under metal roofs for that very reason , the difference in that use is the condensation is not trapped , it rolls down the roof on top of the Tyvek and out the eves . The corrugations also provide ventilation .
