Replies

1. 
   brian_wiley | Sep 29, 2020 06:37pm | #1

   Hi, Reno, welcome to the forums.

   Martin Holladay has a couple of articles that would be of interest in regards to your tape question. They’re great in that they explore a lot of options, some of which may be more effective and cheaper in your case. https://www.greenbuildingadvisor.com/article/return-to-the-backyard-tape-test

   When you say “ Interior walls in the garage will also be OSB (except wall leading to home)“, do you mean that you’ll be hanging OSB as a replacement for the drywall? That is, OSB will be on the interior walls of the garage?

1. 
   Renovations102 | Sep 29, 2020 07:08pm | #3

   Hi Brian.

   Yes, 3 of the 4 interior walls in the garage will be OSB. Drywall on the ceiling & on the wall joining the house.

2. 
   Jon_R | Sep 29, 2020 06:46pm | #2

   Here is the info you need for wall design:

   https://www.appliedbuildingtech.com/system/files/200311_abtg_rr_1701-01_moisture_control_guidelines_figure_update_final.pdf

1. 
   Renovations102 | Sep 30, 2020 09:20am | #5

   Thank you. I read it, but it does not specifically answer my question...

3. 
   Deleted | Sep 29, 2020 07:09pm | #4

   Deleted

4. 
   Renovations102 | Sep 30, 2020 09:28am | #6

   Additional reading has not clarified the issue. Some are saying in zone 5, you need a vapor barrier like membrain over the rockwool, on another site I saw this statement "Because of its greater density and water resistant properties, mineral wool acts as a vapor barrier and, unlike fiberglass, does not need an additional vapor barrier to be effective."

   To be clear, the garage will be heated & cooled via mini-split as needed, OSB exterior walls, no idea what is between that and the vinyl siding. The interior side walls will be OSB as well, the ceiling will be drywall, with R-38 dense-packed cellulose above it (air-sealed & insulated bonus room above garage), and the wall abutting the house is drywalled as well.

   So I still dont' know if a vapor barrier is needed in this situation, or what the benefit would be...

5. GBA Editor
   Kiley Jacques | Sep 30, 2020 09:35am | #7

   I realize your question is hyper-specific but I do think you should read this article, Five Walls that Work. It will shed light on some of your control-layer-related inquires.

1. 
   Renovations102 | Sep 30, 2020 10:22am | #8

   Thank you, looks like I need a membership or something to read it though...

6. 
   brian_wiley | Sep 30, 2020 10:28am | #9

   I’d say go with a smart vapor retarder such as MemBrain if you’re use Rockwool (and, I would go with Rockwool as well for the higher R-value).

   That said, I think your wall would still likely work if you omitted the vapor retarder as you’re air sealing the sheathing and you have vinyl siding, which inherently allows the sheathing to dry as though it had a rainscreen. The other component that helps
   is that this is a garage, so it likely won’t see the moisture loads that a usually occupied space would see.

   These are all assumptions of course, and any one or all could change in the future, which is why I’d probably include the smart membrane if it were me.

1. 
   Renovations102 | Sep 30, 2020 10:29am | #10

   Thanks again, Brian!

7. 
   Jon_R | Sep 30, 2020 11:14am | #11

   Re response #5

   Table 2A. Say that your exterior layer (just OSB?) wet perms = 4. This leads to a Class I interior side vapor retarder in Z6 and a Class II in Z5. Say that interior layer OSB dry perms is 1.5. In this example, you are OK in Z5 but not in Z6.

   Air sealing the interior side is a good idea.

1. 
   Renovations102 | Sep 30, 2020 11:29am | #12

   Hi Jon,

   I saw that, I just don't know how figure the wet & dry perms, never done it before.

   And for info, this is rockwool techs response to vapor barrier:

   "ROCKWOOL is a vapor open product… air and vapor can slowly diffuse through it so will not act as an air or vapor seal."

   And I'm air-sealed with tape, some contolled bead foam from pro gun, and NP1 caulking, depending on what was being sealed...

1. 
   Renovations102 | Oct 05, 2020 09:03am | #13

   Thanks for all the help. I went with Rockwool & Membrain...