Vapour Barrier Attic

In existing spaces oil based paints or vapor barrier latex paints offer an effective moisture barrier.

Vapour barrier attic.

Attic vapor barrier detail for cold climates. The paper facing contains a layer of impermeable asphalt that prevents water vapor from passing through it. A vapor retarder is a material used to prevent water vapor from diffusing into the wall ceiling or floor during the cold winter. The inner surface in colder climates and the outer surface in hot humid climates.

Vapor barriers are sheets of plastic or other material placed on one side of insulation sheets. Even though we apply vapor barriers to exterior insulated walls in cold climates it s no longer recommended for ceilings floor of the attic. A plastic vapor barrier is best installed in a vented attic within climates with over 8 000 heating degree days. Vapor barriers are usually best installed on the side of the wall that experiences the hotter temperature and moister conditions.

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. Rose 1997 regales readers of this history. Because it s nearly impossible to seal penetrations in the ceiling the reality is water vapor will get into the attic. A vapor barrier in an attic assembly in a severely cold climate with the absence of an air barrier will likely be ineffective.

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. In any case the vapor barrier must point to the warm side. It is frightening indeed that construction practices can be so dramatically. 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.

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. Vapor barriers are also a cold climate artifact that have diffused into other climates more from ignorance than need. This barrier is meant to keep moisture from getting to the insulation in the walls and ceilings and it is required by building codes when insulating most houses.