Vapor Barrier needed with blown-in?
68104.1 |
I just put up an addition for a client and fellow FH reader; used the new John’s-Manville “Spider” brand blown fiberglas (sticky; blown into open stud cavities before drywall). The ceiling rock was put in first, then 8″ of dry ‘glas blown in there. My rep says no vapor barrier is needed or used in walls or ceiling, but what do you guys think? Is paint gonna’ do it? The house is near Atlanta, addition is 16’X24′, 1-story on slab, 2×6 @ 24″ OC, framing techniques from the recent FH article, with the header hangers and drywall clips, 1″ of blue foam on the outside, taped and foamed TIGHT, dbl-insulated vinyl windows and doors. Part of the addition is a master bathroom with shower, but with a good (quiet)exhaust fan and a FS series skylight over the shower. VB or no VB? I want to hang the wall rock tomorrow . . . Forrest |
Replies
There needs to be one VB in the walls and ceiling and NO MORE than one. Paint is NOT a VB. Exampes of VB are plastic films, foil and any other sheet materials labeled as being VB. If the "blue foam" is foil or mylar-backed, you're OK. Still need something in the ceiling.
DG/Builder
What is really needed control of vapor tranmission, not nessecarly a vapor barrier.
And a impervious barrier on the inside would not be appropriate in your climate.
See http://www.buildingscience.com/housesthatwork/hygro-thermal.htm
Most water vapor moves with movement of air through the walls. With dense types of insulation (dense pack celsulose and foam) that controls the air movement enough that other means are not needed except in the very coldest climates.
I don't know if your system falls into that classification or not.
You might want to check JM's website.
There are VB primers out there. I had to use some to rectify a problem I got myself into.
Garett
I guess this is a little late, but an interior vapor barrier is not appropriate in Atlanta unless you're looking to farm mold in the walls.
Andy
"Never try to teach a pig to sing. It wastes your time and annoys the pig." Robert A. Heinlein
"Get off your dead #### and on your dying feet." Mom
No VB used - thanks for all the info.
Forrest