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TOPIC: Insulation Concerns

Pole Barn Ceiling Insultion

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I'm at the insulation/drywall stage of converting half of my 1700sq ft pole barn shop into an apartment for cancer-fighting mother. I want to finish the vaulted ceiling with drywall. Between the trusses are 2x6 purlins 24"OC, above those is vinyl-backed fiberglass batting and over that is the metal roofing. Can I remove the vinyl backing (as I did for the walls) and add fiberglass insulation between the purlins and then drywall over (under) that? My concern is about venting and condensation. Another idea I had was to nail 2x4's 16"OC across the purlins and then the drywall. This would serve 2 purposes - one to better attach the drywall to prevent sagging, and two, to create a channel for air to circulate from the top of the wall to the peak of the ceiling. Anyone out there have some suggestions. You can view a few pics here: http://www.michaellobby.com/pbapt.html Thank you for your help!
Michael Lobby

12/2/2010
The air circulation should be right underneath the roof deck and not between the ceiling and the roof deck. The insulation is already there so I would leave what is in place because I think you will have problems removing it and setting the roof back. Your proper insulation layer should be the other side of the finished ceiling. I would fill those 2x6 cavities with the proper insulation depth and then make sure you have a complete and proper vapor barrier that will not allow any humidity to leave the space and collect against the roof line.
Eric Novotny
An informed customer is the Best Customer!

12/3/2010
I can remove the vinyl backing pretty easily, revealing the thin layer of fiberglass (that's right against the metal roof). That fiberglass stays in place and I would add to it with 6-1/4 in. x 23 in. R19 Batt Fiberglass Insulation with paper backing toward the room. The drywall would go directly over that. When you say "proper vapor barrier" should I cover the insulation (paper side) with plastic before the drywall. Thank you for your reply.
Michael Lobby

12/3/2010
The kraft facing on the fiberglass is not a proper vapor barrier because it is not complete and unbroken (i.e. the gaps will allow air/humidity to pass through). Don't bother with removing the plastic on the existing insulation and you really don't need the kraft faced batts. Install unfaced batts and put up a 6 mill poly barrier prior to drywalling. Seal the seams and seal up at the edges.
Eric Novotny
An informed customer is the Best Customer!

12/6/2010