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Discussion Starter #1 (Edited)
I'm still trying to discern what would be best for my situation. I had my sights set on and posted here regarding wet spray cellulose, but mold issues are worrisome. After reading many articles on moisture issues, air pressure principals, vapor barriers, thermal bridges, etc., I may be leaning more toward foam for the outside walls of my garage-to-office reno.

I live in a hot, humid climate (southeastern U.S.)

The outside walls are facing west and south. The west wall is newly built 2x6 treated wood (removed garage door), 10' long with a 72" w x 44' h DI LowE argon gas window.

The south wall is existing 2x4 studs with blackboard and a brick exterior, 20' long. I converted it to a staggered wall to compensate for its "crookedness', i.e., not following the header atop the wall (it was originally a carport converted to garage by previous owner and was an inch off from one end to the other, making sheetrock problematic). This wall is not entirely decoupled, but mostly.

I will also need to insulate behind a 4"w x 3'd x 8'h shower, mostly outside wall (south and east). The shower will be lined and durocked (or perhaps kerdi, but I already have quality shower liner for behind the durock)

So the question is, would foam be the best bet here? And, if so, should I have the existing studs foamed over as well, providing a complete thermal break? Any issues behind the shower with foam with a completely sealed liner?

My goal is to have a wall that holds up under hot wet summer conditions. A/C is not a problem. Sized with fresh air in mind to pressurize the space.

If I go with foam, the inside walls and ceilings will be fiberglass batts.

I'm looking for the best possible solution. I want to do this one time only. No point in doing it all again in my old age, which is fast approaching :).

Thanks!
 

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Foam to the outside wall is a well accepted practice and does quite a bit to affect the overall wall R-Value by interrupting the thermal bridge of the stud.

If you can go that route, that is the best way and will allow you to use more traditional insulations (i.e. FG, cellulose) with better success.

Wet spray cellulose is fine as long as you follow the manufacturers drying recommendations.

Make sure your details on the foam are spot on and staggered seams.
 

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Discussion Starter #3
Foam to the outside wall is a well accepted practice and does quite a bit to affect the overall wall R-Value by interrupting the thermal bridge of the stud.

If you can go that route, that is the best way and will allow you to use more traditional insulations (i.e. FG, cellulose) with better success.

Wet spray cellulose is fine as long as you follow the manufacturers drying recommendations.
So are you saying that foam should be used in addition to other insulations? Is it inadvisable to use only foam on the outside walls? Doing the job right is the priority, but budget is an issue here also. FG might be a bit difficult with the staggered wall, cripples, etc.

Make sure your details on the foam are spot on and staggered seams.
I'm not quite clear on what you mean here either. Are you referring to coverage? Thank you.
 

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Discussion Starter #5
Thanks for the clarification. I suppose I could remove some of the cripples of the original stud wall (20' south wall) to make FG over foam installation more feasible (support is not an issue since there are 2 steel posts and a 12" double header supporting the wall).

If I were to go with the cheaper foam/FG route (as opposed to Foam/Cellulose), would a kraft faced VB facing the living space be neccessary (or even advisable)?
 

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If I were to go with the cheaper foam/FG route (as opposed to Foam/Cellulose), would a kraft faced VB facing the living space be neccessary (or even advisable)?
No. Don't use any kraft backed insulation regardless.
 

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Discussion Starter #7
Thanks for your remarks. I trust the opinions of the regulars here and it has helped in my decision making process many times.
 

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Discussion Starter #8 (Edited)
One more detail...behind the shower. Given that the liner/kerdi/whatever would be akin to a vapor barrier, are there any compensatory steps or different methods required? Normal (not staggered) 2x4 stud wall, blackboard, brick exterior. Foam and non-kraftFG, just foam, just FG?
 

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Discussion Starter #9
Anyone have any thoughts about what method to use when insulating behind the shower and whether the liner presents a vapor barrier issue?


Also, what is the general consensus regarding the home depot foam kits? I'm having trouble generating interest in such a small job.
 

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Discussion Starter #11
If you are concerned about the area behind the show, use something like a rockwood in lieu of the fg.

Make sure you kerdi details are spot on and you should be fine.

I guess I'm not sure what would be best for behind the shower. Is there any reason to be concerned? I had planned on using the heavy liner, sealed, durock because my tile guy prefers durock. But my concern was (durock or kerdi) that the sealed material would create a vapor barrier that might retain moisture. Can I use foam and FG or Rockwool?

And again, given that this is a small job and insulation companies (thus far) interest seems low, any opinions on the DIY foam kits available (i.e., quality, usability)? I found these two, which don't seem all that cheap. The green foam is $609 to handle my Sq footage (around 300 sq ft):

http://www.sprayfoamdirect.com/

http://tigerfoam.com/
 
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