Lance 9000 Project

wannabegone wrote:
From what I understand the Pactiv house wrap I got from Lowes "breaths" it is supposed to keep outside moisture out while the inside moisture is allowed to exit through the material. Are you saying that an RV is too small for the Pactiv to act as designed. I am only using the Pactiv as another guard against outside moisture getting to the wood work. I would hate to add it and find it is doing the opposite of what I was hoping it would do. When we are using the camper I'm sure we will crack one of the roof vents the help excess moisture from ourselves escape like we do on out TT

The "Pactiv house wrap" should be the equivalent of Tyvek or Gore-Tex. These materials are perforated with small holes, too small for blobs of condensed wet water to leak in, but large enough to pass single dry-vapor water molecules out. This should work just fine for outer wrap as long as the inner, warm-side vapor barrier is intact. I would use 6 mil polyethylene inside.

These "outer-wrap" materials do slow evaporation to the outside down, but the trick is to block inner warm dry vapor from migrating into wall cavities much more than the outside vapor escape route, if that makes any sense.

JoeChiOhki is correct that inner paneling cannot be glued to polyethylene sheeting. However, if gluing is important for strength, the paneling can be possibly sealed as a vapor barrier another way.

In my own full size home, I did extensive rebuilding and remodeling. The home was built in the '50's right after WWII. The drywall method was used to sheath the interior. Since I replaced the siding, I added missing insulation from the exterior and saved the old drywall install as undisturbed. Therefore it was not possible to add a polyethylene sheet vapor barrier from the inside. To make up for this, I used a vapor barrier paint on all exterior walls and ceilings to bring the vapor penetration down to a rating of one Perm. This barrier-paint could be done on interior RV paneling, especially if joints were caulked first. Such application would also match color better than multiple types of replacement wood panel and a pleasant light top color would improve lighting.

Another way to apply a slippery plastic vapor barrier seal would be to cover the interior with polyethylene sheet and then cover that with another mechanically fastened lightweight material, even fabric. Screen molding wood battens can help secure fabric even on ceilings.

If the camper were to be used almost exclusively in winter, I would seriously consider covering right over the windows with continuous clear polyethylene. Winter venting can be done with an ordinary roof vent, or better yet, a home-made heat exchanger connected to a roof vent.

Wes
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