Seeking Advice, Knowledge, Past Experience:
Garage Ceiling with Living Space Above. SE Wisconsin climate. The ceiling/floor is insulated. A simple grid style drop ceiling would be nice to allow the insulation to breathe on that side, but can it be done safely? Seems that a painted DW ceiling, even w/o VB will not breathe enough and could result in damp insulation.
Replies
Jim, There are firerated suspended systems, essentially dressed up panels with gypsum cores. However, letting insulation breath from the bottom sounds like something defeating the purpose of insulating from the unheated garage.
Remodeling Contractor just outside the Glass City.
Quittin' Time
I don't know any other way to put it. Breathe might connotate a little more free-flowing air than I have in mind; however, it is my understanding that I don't want to poly those joists before putting up sheetrock. When I think about that insulation getting damp from cold moist air below (e.g., wet cars) and warmth penetrating from above (living space). . .I think that even drywall and no poly will be too restrictive.
Any thoughts?
You might to post this at JLC http://www.jlconline.com on Mike O'Handley forum. My understanding is that you don't have to worry very much about cold moist air since cold air cannot hold a lot of moisture and that the dew point in the insulated floor assembly will not allow the moisture to condense in the insulation. I think that you should install a vapor barrier on top of the joists and insulate below.
Thanks for the referral. I found this thread and it looks like the best course of action is to not use a VB on the cold side, and that the OSB sub floor has a low enough perm rating for the warm side. I will be adding another layer of 1/2 ply to the subfloor prior to adding finished flooring, too (for other reasons)
http://www.jlconline.com/cgi-bin/jlconline.storefront/402e1cca003a2b52271a401e1d2905b1/Catalog/1135?read=10894
Jim, Check the local codes for any fire barrier. Last time I checked the massachusetts state building code, it required a 1 hour rating. Even if there is no local code stating a fire wall I would install anyways.
No good deed goes unpunished
Around here (MA), it is standard practice (and, as stated above a code requirement) that living spaces be separated from garages. This is usually done with 5/8" drwyall, either Firecode Sheetrock or 5/8 blueboard and plaster. I really don't think your concerns about breathing are anything to worry about. The biggest mositure problem I see in garages is stuff leaking from above and damaging the ceiling, but that's another problem.
Even this requirement is no guarantee. A couple of years ago, a new Beamer combusted spontaneously in the garage of a new home in town. The family survived, perhaps because the drywall gave them some time, but the entire house was destroyed by the ensuing blaze. These things do happen, so it's good you're planning to do something. I'm kinda glad my old house has a detatched garage.
Al Mollitor, Sharon MA