Some insulated ceiling assemblies include a vapor barrier to prevent moisture in the air from migrating from the warm heated side of the ceiling to the cold outer area of the assembly where it.
Attic ceiling vapor barrier.
In existing spaces oil based paints or vapor barrier latex paints offer an effective moisture barrier.
We complicate things when we install plastic in ceilings and assume it provides an air 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.
Almost 6 years by bv006343.
A vapor retarder is a material used to prevent water vapor from diffusing into the wall ceiling or floor during the cold winter.
With spray foam unlike with loose fill or batts you must cover the soffit vents they aren t needed to keep the roof cool.
Basement ceiling vapor barrier.
Conversely an air barrier in absence of a vapor barrier can be effective.
A plastic vapor barrier is best installed in a vented attic within climates with over 8 000 heating degree days.
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.
Even though we apply vapor barriers to exterior insulated walls in cold climates it s no longer recommended for ceilings floor of the attic.
Then cover the foam with drywall as required for fire safety.
A vapor barrier in an attic assembly in a severe cold climate in absence of an air barrier will likely be ineffective.
Attic vapor barrier detail for cold climates.
Because it s nearly impossible to seal penetrations in the ceiling the reality is water vapor will get into the attic.
Foam blocks airflow needs no vapor barrier and has a higher r value per inch than loose fill or batts so you ll get more protection with less depth.
The inner surface in colder climates and the outer surface in hot humid climates.
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 vapor barrier in an attic assembly in a severely cold climate with the absence of an air barrier will likely be ineffective.