The inner surface in colder climates and the outer surface in hot humid climates.
Attic ceiling vapor barrier.
To know if you need a vapor retarder ask yourself a few basic questions.
A vapor barrier in an attic assembly in a severely cold climate with the absence of an air barrier will likely be ineffective.
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.
A vapor retarder is a material used to prevent water vapor from diffusing into the wall ceiling or floor during the cold winter.
Even though we apply vapor barriers to exterior insulated walls in cold climates it s no longer recommended for ceilings floor of the attic.
Because it s nearly impossible to seal penetrations in the ceiling the reality is water vapor will get into the attic.
We complicate things when we install plastic in ceilings and assume it provides an air barrier.
Vapor barriers are usually best installed on the side of the wall that experiences the hotter temperature and moister conditions.
Then cover the foam with drywall as required for fire safety.
Basement ceiling vapor barrier.
Almost 6 years by bv006343.
The attic studs and floor of the garage attic are configured in a way to allow the space to be finishe.
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.
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.
With spray foam unlike with loose fill or batts you must cover the soffit vents they aren t needed to keep the roof cool.
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.
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.