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Old 11-14-2011, 09:40 AM
 
Location: Atlanta, GA
1,123 posts, read 6,537,574 times
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This is a follow up to a post from months ago I did around insulating for a room above the garage. What I ultimately decided to do was dense pack the garage walls and ceiling with cellulose. However, this will still leave two major culprits of making that room uncomfortable (esp. during the brutal Georgia summers)...the knee walls and cathedral ceiling of the room. I have been researching using blown in dense pack in these applications and creating an "unvented" roof (currently there are soffit vents, but only a gable vent at the end of the garage roof). I have read that some people warn against this application but it seems most of the horror stories of rotting roof decking are in very cold climates where sometimes the indoor humidity is higher than the outdoor humidity. In Atlanta, this is rarely the case. I was hoping to get some opinions on this topic from other board members to see if it's a worthwhile endeavor prior to next summer. Once I have the room properly insulated I would install a mini-split ductless A/C and heating device.

Thanks!
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Old 11-14-2011, 01:19 PM
 
Location: Johns Creek, GA
17,474 posts, read 66,045,317 times
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I have several pdf's on the subject but, there all too big for C-D. Here's one I tracked down:
Article #134 - Rigid Board Insulation Installed as Draft Stop in Attic Kneewall - Code Notes

And from a previous post of mine (w/illustrations):
https://www.city-data.com/forum/16816615-post9.html
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Old 11-14-2011, 05:53 PM
 
28,455 posts, read 85,370,617 times
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Rot rarely happens "outside in" on a roof -- you would need to a veritable jungle of trees / vines /rain water to destroy the shingles and such.

That said even a little bad weather (ice / freezing rain) in a poorly vented roof design COULD trigger some massive condensation issues if the moisture level inside the house is unchecked...

Before I would dense pack a cath ceiling I would give serious thought about foam. As long the area is not HUGE the price offset would be well worth the piece of mind.
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Old 11-15-2011, 06:41 AM
 
Location: Atlanta, GA
1,123 posts, read 6,537,574 times
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Well, I was thinking dense pack cellulose because I was leaning towards that method for insulating the garage walls/ceiling beneath this room. Spray foam would probably be ideal, except the room is already finished (although appears to be a DIY special, so not perfectly done), so I would prefer to not tear it all down to insulate. This led me to researching dense pack in the ceiling and filling the soffit/knee wall areas as well to minimize air flow. I track humidity in my house year round and the highest it ever gets is 50% if I leave windows open in Spring/Fall. Summer is 45% (due to AC) and Winter gets really low (sometimes below 20%). I had the roof done 3 years ago with standard roof felt and 30 year timberline shingles, so water or vapor transfer from outside shouldn't happen, and with the humidity inthe house being below outside most of the time, I would think there would be minimal transference from inside out.
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Old 11-15-2011, 08:31 AM
 
Location: Johns Creek, GA
17,474 posts, read 66,045,317 times
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The "problem" with doing a post-construction dense pack install is- you'll never know for sure if it's ALL dense packed.
You say the finish of the room looks DIY- that says, who the Hell knows what's behind the walls.

In the grand scheme of things- drywall is cheap.
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Old 11-15-2011, 10:00 AM
 
Location: Atlanta, GA
1,123 posts, read 6,537,574 times
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Quote:
Originally Posted by K'ledgeBldr View Post
The "problem" with doing a post-construction dense pack install is- you'll never know for sure if it's ALL dense packed.
You say the finish of the room looks DIY- that says, who the Hell knows what's behind the walls.

In the grand scheme of things- drywall is cheap.
Good point...I guess I could do the dense pack for the garage below, including the ceilings, and then see how things go. If the room is still unbearable, then I can tear it down and have spray foam at a later date.
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