Originally Posted by teknomad
I was thinking of installing 'house wrap' vapor barrier around the entire interior, before putting insulation in. The goal is to help make the interior air-tight, prevent drafts, etc.
I was thinking the layers should be:
body metal > Plastic Wrap > insulation > wood > floors/wallls?
Im concerned with moisture buildup between the metal and plastic. Or really, anywhere in the bus. What is the best order to put these materials in?
This will be in Canada, so there is moisture and lots of temperature variations.
To be clear, house wrap like Tyvek is infiltration barrier, not vapor barrier. It slows leaks, which is a good thing in itself. It's installed on the exterior of houses to reduce air infiltration through cracks.
Vapor barrier = plastic sheeting. In residential construction this goes behind the sheet rock and prevents the warm humid air on the inside from coming into contact with the exterior of the building envelope where it could reach dew point and condense.
The vapor barrier needs to prevent the inside air from reaching dew point, so it needs to be on the inside of whatever insulation or thermal bridging you have. On a bus, there will always be some wood or metal almost in direct contact with the air inside of the bus, sadly.
So it is somewhat a balancing act. The idea is to minimize the number of places on the inside of the bus that go below dew point, by a) minimizing those cold points of conduction on the interior and b) keeping the inside temp high enough and air circulation great enough that stagnant air has a harder time cooling. Air circulation is important because it helps evaporate any condensate.
Tools in the tool box: vapor barriers; insulation; heaters; fans; other thermal bridging products to reduce heat/cold transfer. I'd add dehumidifier to the list if it wasn't so energy-intensive.