Vapor Barrier for Filling in Missing Insulation

[aghahary]

Hello Everyone,

I have an old house built in the 1960's, and have noticed the celing has some spots where there is no insulation between the house and the attic. One of the easiest things I can do is to throw in cellulose insulation in those "cavities". My question is that do I need to place some kind of vapor barrier/retarder down first, or can I just throw the insulation in?

Thanks for any feedback.

[t527ed]

i would put some plastic doown first, moisture under the insulation would be a bad thing.

[teddy bear]

Vapor barriers are not as critical as once thought. The critical issues are air tight and maintaining low humidity on the inside of the house. +40%RH during extreme cold weather puts vapor pressure on the insulation in the walls and attic insulation. The greatest vapor barrier in the exterior insulation system should be on the predominately warm side of the insulation. Areas like bath rooms with showers are critical for the vapor barrier location. Season Greetings Regards TB

[teddy bear]

i would put some plastic doown first, moisture under the insulation would be a bad thing.

Moisture condenses on the cold surface not the warm surface. The moisture condenses on the top of the insulation (cold side) not on the warm side during cold weather. In the summer when the attic goes hot, the moisture may condense on the drywall under the insultation. Seasons Greetings Regards TB

[windtunnel]

if you have a properly ventilated attic then no vapor barrier is usually required.