Replies

1. 
   user-2310254 | Sep 04, 2017 01:59pm | #1

   There are some other things about your assemblies that are questionable. Have you read this article: https://www.greenbuildingadvisor.com/articles/dept/musings/how-design-wall

   You can certainly use 2X4 and create an energy-efficient wall, but I don't think either of your stackups are the way to go.

2. 
   LeoPaul | Sep 04, 2017 08:08pm | #2

   Yes I read that article and then came across Greg La Vardera Better and Best Swedish Wall (sorry the link won't pass the spam filter). However since my contractor provided a valid payback argument, I thought I could modify Greg La Vardera Better and Best Swedish 2x6 wall with a 2x4 recommended by my contractor.

3. 
   user-2310254 | Sep 04, 2017 11:46pm | #3

   I found the post on La Vardera's site. Scott Gibson also has a post here about hanging vinyl siding on furring strips. Apparently you can,make it work but some manufacturers are more open to the idea than other. That said, I would have concerns about keeping the strips and siding coplanner. For that reason, I would be more inclined to use Option B. The Zip R without furring would be simpler since vinyl siding seems to dry fine even without a gap.

4. GBA Editor
   Martin Holladay | Sep 05, 2017 05:38am | #4

   L. Philip,
   The three most glaring issues concerning your stack-up proposals are the following:

   1. Most vinyl siding manufacturers do not allow their siding to be installed over furring strips. For more information on this issue, see Can Vinyl Siding be Applied Over Furring Strips?

   2. You seem to want to include a vapor barrier, even though a vapor barrier is neither required by code nor recommended by building scientists. You don't tell us what type of material you want to use for the vapor barrier, but I am guessing that you are thinking of using polyethylene, which is probably not a good idea.

   The building code requires an interior vapor retarder, not a vapor barrier. (A vapor retarder is a less stringent layer than a vapor barrier.) Vapor retarder paint on your drywall is all you need to fulfill this requirement.

   For more on this issue, see Do I Need a Vapor Retarder?

   While your wall does not need a vapor barrier, it certainly needs one or more air barriers. You need to develop an air barrier plan.

   3. The third issue is a warning, not a problem: Installing furring strips on top of exterior mineral wool can be tricky. For that reason, it's a building method that is rarely used. It's not impossible, but you should go down that road with open eyes.

5. 
   LeoPaul | Sep 05, 2017 08:54am | #5

   Steve thanks for the input. I like Option B but I hate OSB. I have a 100 year old house and I/m hoping to closely align quality but trying to stay cost competitive. The zip system Insulated board does look appealing though.

   Martin: Thank you for the extremely detailed fact based answer.

   1. I got the idea from reading way too much. You know everything they say on the we "is true". Also, since don't have single builder's bone in my body, I could have mis construed the information.

   2. Yes, I meant a vapor retarder. I want the walls to breathe. And yes I want to it to be as airtight as possible.

   3. I think the exterior mineral wool is much more expensive than reclaimed rigid board. I think I may have come across a comment by you somewhere that recycled rigid foam is a good option. It's about $20 a board @ 4". That seems to be a good price.

   So maybe this is how it should go: Dry wall, 2x2 furring strip, 2" empty cavity for wiring and pluming, vapor retarder, 2x4 framing w/ R15 roxul, plywood/osb, taped seams, air barrier, 2" reclaimed rigid foam, rain screen, certainteed cedar impressions or lap siding.

6. GBA Editor
   Martin Holladay | Sep 05, 2017 08:58am | #6

   L. Philip,
   Your latest wall design makes more sense. It should work.

7. 
   LeoPaul | Sep 05, 2017 10:15am | #7

   Thanks Martin. I feel like I've graduated 1st grade. Much appreciated.

8. 
   LeoPaul | Sep 05, 2017 11:55am | #8

   Martin: in another Q&A you mentioned that if one were to use rigid foam on the outside, then you should be careful in used inside insulation, did I misunderstand? Would the use of Roxul on the inside without a vapor retarder but an air barrier be a problem in my wall design? I'm in Zone 4 outside of Philadelphia.

9. Expert Member
   MALCOLM TAYLOR | Sep 05, 2017 12:31pm | #9

   L. Philip,
   Unless you are intending to insulate the 2"x2" service cavity, is it really worth including? It represents a fair amount of additional labour, and if you aren't using the vapour retarder as an air-barrier protecting it isn't that Important, nor are any penetrations that the wiring and plumbing would create if they were in the main stud space.

   It might be worth looking at what the service space will actually contain. What plumbing fixtures are on exterior walls? An 1 1/2" cavity isn't big enough for any drains, so really what you end up with is a couple of water supplies that could be routed through the floor and a few wires.

   2"x2" service cavities make sense with Mooney walls insulated with cellulose, where they reduce thermal bridging. I don't see much benefit otherwise.

10. GBA Editor
    Martin Holladay | Sep 05, 2017 12:54pm | #10

    L. Philip,
    A wall with an adequately thick layer of exterior rigid foam does not require an interior vapor retarder (because the wall sheathing will never get cold enough for moisture accumulation or condensation).

    It's perfectly OK to use mineral wool batts between studs when insulating a wall with exterior rigid foam.

11. 
    LeoPaul | Sep 05, 2017 01:08pm | #11

    Thanks Martin! You guys are the best!