Tvyek versus bubble wrap as vapor barrier?

[loess]

I was reading Bob's blog post about Richard's van insulation and saw that he had put Tyvek against the metal skin of the van, followed by bubble wrap > Reflectix > 1" styrofoam > NRP board. I'm wondering why one would feel the need to apply a layer of Tyvek beneath the bubble wrap? Wouldn't the bubble wrap itself serve as a vapor barrier? For my insulation I was planning to go with bubble wrap (to serve as vapor barrier and air gap) > Reflectix > 1/2" Polyiso > Coroplast, but if it is worth it to hunt down some Tyvek for the additional layer I will do that. Just trying to plan my layers as carefully as possible to avoid rust/mold issues later on down the road...

I have read up on the subject of insulation extensively and have done my best to search the forums on this so I hope I am not rehashing a question that has already been answered!

 

[Optimistic Paranoid]

Tyvek is NOT a vapor barrier. It says so right on the FAQ page on the Dupont Tyvek site.

Regards
John

 

[Patrick46]

Tyvek will do little to nothing against the walls of a van.

You wrap a house in it on the outside of the plywood sheeting, but underneath the siding. It's a breathable material (thus not a vapor barrier) that helps keep water out. A van doesn't need this under it's skin, as it shouldn't have any water under there in the first place.

If it does, then you've got bigger issues to deal with.

 

[loess]

That clears it up. Will skip the Tyvek. Thanks y'all

 

[offroad]

Bigger issues being lack of insulation. Humidity in air condense on wall. Only condensation should be on the window. Do wooden structural walls rot-rust because of water condensation or because of water leaks?

 

[akrvbob]

Unless you are leaving an air space, the Reflectix is useless as insulation and you are just wasting your money. According to their website it is R 1 without an air space. For comparison, polyiso is R6. Without an air space it does not work to reflect heat.

Bob

 

[loess]

I will be putting bubble wrap on either side of the Reflectix to serve as air space, but its always good to have that bit of info in a thread like this in case somebody comes across it in the future! thanks Bob

 

[akrvbob]

Right, I see. That makes prefect sense, it holds the space and even adds a little insulation. Good idea!
Bob