The wetter it gets the better it dries.
Where does vapor barrier go in attic.
In any case the vapor barrier must point to the warm side.
Adding a second vapor barrier could cause condensation to become trapped in the insulation between the two vapor barriers.
Vapor barriers are also a cold climate artifact that have diffused into other climates more from ignorance than need.
Attic vapor barrier detail for cold climates.
What role does a vapor barrier play.
Whether or not you need a vapor retarder hinges on three main factors.
If you put it on the right side where the humidity is it s not much of a vapor retarder.
Most authorities now agree that vapor barriers are important under certain conditions but not necessarily as a whole house solution for every home.
Not every wall does.
This essentially means that in the winter vapor inside your home will want to move into your attic where it is colder.
Because it s nearly impossible to seal penetrations in the ceiling the reality is water vapor will get into the attic.
It is frightening indeed that construction practices can be so dramatically.
Vapor barriers are sheets of plastic or other material placed on one side of insulation sheets.
Within your attic there is free movement of air and vapor and water vapor tends to move from warmer to colder spaces.
Also on the graph is the permeance of polyethylene.
Not so asphalt saturated kraft paper.
Even though we apply vapor barriers to exterior insulated walls in cold climates it s no longer recommended for ceilings floor of the attic.
In circumstances where conditions inside a home or office are much different than outdoor conditions water.
Over time this trapped moisture can rot the wood framing in your attic or cause mold and mildew to appear.
Rose 1997 regales readers of this history.
Joe says in the article plastic vapor barriers really are vapor barriers when things get wet.
After the insulation is in place you will want to add a vapor retarder sometimes called a vapor barrier if you need one.
Some debate still occurs over how necessary vapor barriers are but a consensus is growing closer.
On the other hand an air barrier a properly detailed air tight drywall ceiling for example in the absence of a vapor barrier can be effective since it stops the flow of vapor laden air.
In the summer the reverse occurs.
The history of cold climate vapor barriers itself is a story based more on personalities than physics.
Resolution of the vapor barrier debate.
Warm humid air will move towards.
