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Old 01-06-2012, 08:22 PM   #1
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WSACI questions


I have closed in a garage in order to make office space. I’ve reached the stage where, after my pending framing inspection, I can insulate. I’d like to use wet spray applied cellulose on the walls and R-19 bats for the ceiling (2x8 joists with attic space above, attic floor is decked).
Pertinent information:

1. Climate is hot/humid deep southeast U.S.
2. There are 2 outside walls with brick exteriors.
Wall 1:
20’x8’ wall facing south (with staggered stud construction, top 1’ of wall is a double 2x12 joist header). Blackboard sheeting.
Wall 2:
10’x8’ wall facing west, 2x6 stud construction, top 1’ is 2x12 double joist header. This wall will accommodate a 72”x44” twin window (S.H., D.I., low e, argon gas). This is new wall, still deciding whether to use blackboard or plyboard.

Wall 3 (adjacent to living space) is also a staggered stud wall for purposes of sound proofing. This wall will have double 5/8 drywall on both sides with greenglue in between the layers. I propose to use cellulose here as well, although a lighter layer.

Wall 4

May also receive a light coating of cellulose. 2 doors (from living space and bathroom) are on this wall.

The 8’x4’ bathroom has an east facing wall (4’) and a south facing wall (8’), both brick outside. A 4’ wide x 3’ deep shower will cover all of the east wall and half of the south wall, half of living space wall. All walls in the bathroom will receive cellulose as well, again for both temp and sound control.

3. This space will have a 1 & ½ ton A/C with fresh air added as needed. Bath exhaust will help equalize the pressure.

Questions:

1. After reading up a bit on cellulose, some opinions are that mold can be a real issue. If true, what steps can I take to prevent it?
2. How much time should I allow for the WSACI to dry before drywalling? I can run the heater if necessary.
3.* Is a vapor barrier required? There seem to be varying opinions on this. Some say that it is unnecessary and increases chances for mold.
4. * For the shower, I will be using a heavy shower liner (seams sealed with shower pan adhesive) and durock. Will this present any problems for cellulose?
5. And finally, for wall 2, I’d like to use plyboard rather than blackboard. Is this a great loss in R-value?

Sorry for the length of the post, but I always think better to have more info than less. Thanks for any opinions.

Edit: I also should say that the existing blacboard on wal l 1 has various holes in it (ranging from quite smalll to 2"). What is the best method to cover those in conjunction with the cellulose?

Thanks,
Mark

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Last edited by rightit; 01-06-2012 at 08:50 PM.
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Old 01-08-2012, 12:00 PM   #2
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WSACI questions


Quote:
Originally Posted by rightit View Post
I have closed in a garage in order to make office space. I’ve reached the stage where, after my pending framing inspection, I can insulate. I’d like to use wet spray applied cellulose on the walls and R-19 bats for the ceiling (2x8 joists with attic space above, attic floor is decked).
Pertinent information:

1. Climate is hot/humid deep southeast U.S.
2. There are 2 outside walls with brick exteriors.
Wall 1:
20’x8’ wall facing south (with staggered stud construction, top 1’ of wall is a double 2x12 joist header). Blackboard sheeting.
Wall 2:
10’x8’ wall facing west, 2x6 stud construction, top 1’ is 2x12 double joist header. This wall will accommodate a 72”x44” twin window (S.H., D.I., low e, argon gas). This is new wall, still deciding whether to use blackboard or plyboard.

Wall 3 (adjacent to living space) is also a staggered stud wall for purposes of sound proofing. This wall will have double 5/8 drywall on both sides with greenglue in between the layers. I propose to use cellulose here as well, although a lighter layer.

Wall 4

May also receive a light coating of cellulose. 2 doors (from living space and bathroom) are on this wall.

The 8’x4’ bathroom has an east facing wall (4’) and a south facing wall (8’), both brick outside. A 4’ wide x 3’ deep shower will cover all of the east wall and half of the south wall, half of living space wall. All walls in the bathroom will receive cellulose as well, again for both temp and sound control.

3. This space will have a 1 & ½ ton A/C with fresh air added as needed. Bath exhaust will help equalize the pressure.

Questions:

1. After reading up a bit on cellulose, some opinions are that mold can be a real issue. If true, what steps can I take to prevent it?

Make sure that the exterior wall is air tight. The issue is a warm, muggy climate will the the migration of humidity into the wall cavity and resultant dewpoint conditions with cooler interior framing/wall assemblies. Bulk air movement will carry much more moisture than diffusion.

2. How much time should I allow for the WSACI to dry before drywalling? I can run the heater if necessary.

Check with the material manufacturer and defer to their recommendations.

3.* Is a vapor barrier required? There seem to be varying opinions on this. Some say that it is unnecessary and increases chances for mold.

The consensus is no and certainly not towards the interior of the home. Stop the air movement and you should be fine and especially with a staggered wall. It would be nice to have a thermal break across the studs to interrupt heat transfer and condensation locations, however, the wall should be able to dry to both sides in most cases. I am not sure of the perm ratings on blackboard are but is is probably class 2 or higher.

4. * For the shower, I will be using a heavy shower liner (seams sealed with shower pan adhesive) and durock. Will this present any problems for cellulose?

Not if done properly. Durock is somewhat moisture permeable. You might want to look into the Schluter product as it makes the shower completely water tight and despite the fact it is a bit more expensive, makes shower pans and other installations easier in the long run.

5. And finally, for wall 2, I’d like to use plyboard rather than blackboard. Is this a great loss in R-value?

No.

Sorry for the length of the post, but I always think better to have more info than less. Thanks for any opinions.

Edit: I also should say that the existing blacboard on wal l 1 has various holes in it (ranging from quite smalll to 2"). What is the best method to cover those in conjunction with the cellulose?

Thanks,
Mark
See responses in bold print.

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Old 01-12-2012, 04:53 PM   #3
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WSACI questions


Hello again, WoW, and thank you for your comments.

Quote:
1.
Quote:
After reading up a bit on cellulose, some opinions are that mold can be a real issue. If true, what steps can I take to prevent it?
Quote:

Make sure that the exterior wall is air tight. The issue is a warm, muggy climate will the the migration of humidity into the wall cavity and resultant dewpoint conditions with cooler interior framing/wall assemblies. Bulk air movement will carry much more moisture than diffusion.
I'm not sure what you mean by exterior wall...the black board or the brick? And, of course, both are impossible to get 'airtight'. That said, the black board does have some holes in it that I wonder what is the most effective way to seal up.

Again, thanks for your comments.


Mark

Edit: I just talked to a company that proposed to dry blow it with some kind of netting to hold it in the open stud wall? Would that eliminate the mold issues?

Last edited by rightit; 01-15-2012 at 01:01 PM.
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