Replies

1. GBA Editor
   Martin Holladay | May 22, 2018 11:00am | #1

   Corca,
   First of all, can you tell us your name?

   A rainscreen gap provides many useful functions. Installing Zip sheathing doesn't allow you to skip the rainscreen gap. (I suppose you can eliminate the rainscreen gap if you want, but the wall won't perform as well if you do.)

   For more information on rainscreens, see All About Rainscreens.

   A rainscreen gap is particularly important for double-stud walls, since it's important with this type of wall to have a mechanism to help the damp wall sheathing dry quickly in the springtime. For more information on this issue, see How to Design a Wall.

   You didn't really explain where the two layers of 1/2-inch CDX plywood will be. It sounds like the outer layer of plywood will be on the exterior side of the outer 2x4 wall. But what about the inner layer of plywood? Will it be on the exterior side of the inner 2x4 wall, or will it be on the interior side of the inner 2x4 wall?

2. GBA Editor
   Martin Holladay | May 22, 2018 11:05am | #2

   Corca,
   While the manufacturer of Zip sheathing allows builders to skip the housewrap when using Zip sheathing, some builders still install housewrap or asphalt felt as a WRB -- even when they use Zip sheathing -- because these membrane-style materials allow the WRB to be lapped over flashings, shingle-style (something you can't do with Zip sheathing alone). For more information, see All About Water-Resistive Barriers.

3. Expert Member
   MALCOLM TAYLOR | May 22, 2018 11:12am | #3

   Corca,

   "1/2" vertical furring for rainscreen, 3/8" horizontal furring (to accomodate for Hardie board and batt siding."

   Can you clarify why the second layer of furring is necessary? Hardie-board and batten siding can be installed on vertical furring. if for some other reason it is necessary, the horizontal furring needs to be thicker. 3/8" will bow back between the vertical supports.

4. GBA Editor
   Martin Holladay | May 22, 2018 11:12am | #4

   Corca,
   Q. "If the Zip is used on the exterior double stud would air sealing/taping the interior sheathed wall still be necessary?"

   A. If you care about reducing air leakage, it usually makes sense to have redundant air barriers, so yes -- an interior air barrier would be a good idea. But ultimately, the answer to this question depends on your air leakage targets and your budget. For more information on this issue, see One Air Barrier or Two?

5. GBA Editor
   Martin Holladay | May 22, 2018 11:15am | #5

   Corca,
   Q. "If we did end up having to use a conventional, sheet type WRB could we eliminate the need of a rain screen by using Tyvek DrainWrap or HydroGap?"

   A. Wrinkled housewraps provide some drainage, but almost no ventilation drying. If the purpose of your rainscreen gap is to accelerate drying of damp sheathing, then a wrinkled wrap is inferior to a true rainscreen gap. For more information, see All About Rainscreens.

6. 
   Corcakalaka | May 22, 2018 01:04pm | #6

   Thanks for the replies, guys!
   Mr. Holliday- 1. My name is Corey Eshelman
   2. The CDX on the interior stud wall is installed on the exterior side of said wall.
   3. Thanks for the reference articles, I will get to reading them immediately.
   Mr. Taylor- I honestly cannot clarify why the secondary layer of furring is called for, it is just how the plans show it. I am pushing the designers to allow us to use a single layer of 1/2 in vertical coravent.

   So then, gentlemen. Would it behoove us (the build team) to do away with the Zip and proceed with 1/2" CDX>WRB>Vertical Rainscreen>Hardie? Is Tyvek a suitable material or should I look in to a ProClima product, or equivalent?

   Thanks, Guys!

7. GBA Editor
   Martin Holladay | May 22, 2018 01:24pm | #7

   Corey,
   Q. "Would it behoove us (the build team) to do away with the Zip and proceed with 1/2" CDX>WRB>Vertical Rainscreen>Hardie?"

   A. If I understand correctly, you aren't "doing away with the Zip," since evidently the architect specified 1/2-inch CDX plywood.

   Q. "Is Tyvek a suitable material or should I look in to a ProClima product?"

   A. Tyvek works fine as a WRB.

8. 
   Corcakalaka | May 22, 2018 02:05pm | #8

   Mr. Holladay,

   You are correct. And thanks for your valuable suggestions.

   Corey

9. Expert Member
   MALCOLM TAYLOR | May 22, 2018 10:15pm | #9

   Corey,

   You will be better off with 1/2" or 3/4" plywood strips tha Cor-a-Vent if you are using Hardie Panels and Battens. Shooting trim-nails through that much cement-based materials is a bit of a challenge at the best of times, but with the Cor-a-Vent you don't have anything solid to embed the fastener into until it reaches the sheathing. The nails securing the battens would be too long to use the trim-nailers you typically would.

   Edit: This is a picture of a house I did with Hardie-Board and battens on vertical furring at 16" oc. The furring is located over the studs, the nails attaching the Hardie-Board get covered by the battens. The shingles above are cement-based too, fastened to the same battens.

   
10. 
    Jon_R | May 22, 2018 11:43pm | #10

    You might review below to decide if you prefer Typar over Tyvek for lower perms.

    https://buildingscience.com/documents/building-science-insights/bsi-061-inward-drive-outward-drying

    Might also be of interest (even with your different design):

    "Pressure treated strapping is only required in high rain areas, though it is recommended in all jurisdictions. "

    https://static.rockwool.com/globalassets/rockwool-na/downloads/technical-guides/residential/comfortboard80_installation_techguide_en.pdf