Because it s nearly impossible to seal penetrations in the ceiling the reality is water vapor will get into the attic.
Vapor retarder in attic.
A vapor barrier or vapor diffusion retarder is a material that reduces the rate at which water vapor can move through a material.
Some regions don t require a vapor barrier.
Resolution of the vapor barrier debate.
This wall is a further variation of figure 6 but now it has a class i vapor retarder on the interior a vapor barrier completely eliminating any inward drying potential.
Some debate still occurs over how necessary vapor barriers are but a consensus is growing closer.
Applicability limited to very cold subarctic and arctic regions.
Attic vapor barrier detail for cold climates.
The paper facing contains a layer of impermeable asphalt that prevents water vapor from passing through it.
The older term vapor barrier is still used even though vapor diffusion retarder is more accurate.
If your climate does not meet these conditions a vapor retarder like latex ceiling paint will work well for your house if you are in all other climates except the hot dry and hot humid.
A plastic vapor barrier is best installed in a vented attic within climates with over 8 000 heating degree days.
Most authorities now agree that vapor barriers are important under certain conditions but not necessarily as a whole house solution for every home.
Frame wall with cavity insulation and brick or stone veneer with interior vapor barrier.
Whether or not you need a vapor retarder hinges on three main factors your climate your home and the location of the wall you re insulating.
Do not add a vapor barrier on top of the insulation in your attic since the paper facing on the existing insulation is the vapor barrier.
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.
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.
The ability of a material to retard the diffusion of water vapor is measured in units known as perms or.