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Old 06-29-2014, 05:49 PM   #1
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Miami Vaulted Ceiling Insulation (need to seal?)


I live in Miami, and our house (1941) has a typical Miami "converted garage" (probably illegally done without permits - i.e. typical Miami). For those who don't know, it's an attached garage that is converted into a living space - usually an efficiency for relatives/a subletter to live in.

It was in pretty gross condition, and we're in the process of renovating it for use as a TV room area. It has a beautiful vaulted ceiling with exposed rafters and everything (i.e. it's the roof, obviously), but, since we're in Miami, it gets absurdly hot in the summer so we need to insulate and drywall it. The previous owner just had drop acoustic tiles in to create as much of a thermal barrier as he cheaply could, but not only were they old and disgusting, we want the increased volume and beauty of the vaulting.

My question is, then, on whether or not I'll be needing to seal the inside of the roof decking (and then what my options are for that) to prevent moisture/mold growth issues. I'll give you the details of the situation:

-Wood vaulted roof (clay tile roof on top)
-Unvented (no soffits or anything)
-Previously had drop tile ceiling to create a thermal buffer
-Had mold growth on walls (concrete) in between acoustic tiles and the roof (this may have been also because of the air being off in the house for weeks before we bought it)
-Want to keep vaulted ceiling, and not have to create an attic-like situation (i.e. creating a lowered, flat ceiling and then insulating on top of that)

I've done a decent amount of research on this, and found that unvented vaulted ceilings are very doable, happen frequently, and the recommendation is always to seal (usually with closed cell foam) which obviously acts as insulation as well. The problem is, everything I've read is about places that aren't South Florida - i.e. places that experience cold/freezing weather.

Obviously in those places during the winter, warm, moist air inside penetrates into the area in the ceiling, cools as it hits cold roof, condensates, then you get mold and/or water damage. The situation is reversed in Miami, at least during the summer, where hot, moist air is outside, and cool, drier air is inside. I'm wondering if there is still the potential for mold growth, mostly from the hot, moist outside air penetrating through the roofing into the ceiling space where the insulation is. Obviously, this concern is furthered by the fact that there was mold on the concrete walls above the old drop ceiling that was in place (as mentioned above).

So, what do I do? Do I bite the bullet and just seal anyway? The only reason I'm considering not is budget issues, especially if I have to have it done professionally (which I probably should). Also, do I have to have the whole depth of the rafter foam-insulated, or can I just do the first inch with foam to create the seal then put fiberglass batts below it which are cheaper and I can easily do myself?

Or, will I be fine, and can just run fiberglass batts then drywall over?

Also, there is clearly a gap between the roof/rafters, etc. and the concrete walls (i.e. where the roof and walls meet), though it is generally small (no more than 1/8" at any point). I don't know if the roof is properly sealed on top of the decking and such (like it should be, underneath the roof tiles), but I can only hope and assume it is. Therefore, it is possible the air/gas/moisture exchange is coming from the gap here and not through the roof itself, and that would then (hopefully) be why the mold growth occurred. If that were the case, would I then be able to seal just this gap all along, and then proceed with just fiberglass batts and then the drywall?

And if I do need to seal everything, what are my options with that? What is the best, what is the cheapest, what is the easiest, etc. etc.? If I confirm that I do need to seal, I'll have to weigh my options between our budget, my abilities, and time in order to determine how we'll have to proceed.

Anyway, I think that's about it. I hope I've explained things well, but by all means please ask me anything you need to know to give a better answer. And thank you very much for taking the time to read this post and especially if you respond.


Last edited by ShenAmateur; 06-29-2014 at 05:59 PM.
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Old 06-30-2014, 06:40 AM   #2
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Location: VA, MD, DC
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Miami Vaulted Ceiling Insulation (need to seal?)

Post up some pictures and post back a cliff notes version. You will get more feedback.

I read the whole thing but you are not going to like my answer.

Doing is right is rarely the cheapest route from the outset but will cost you less in the long run.

I would use a combination of rigid foam, spray foam, and batt insulation.

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insulation vaulted

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