GBA Logo horizontal Facebook LinkedIn Email Pinterest Twitter Instagram YouTube Icon Navigation Search Icon Main Search Icon Video Play Icon Plus Icon Minus Icon Picture icon Hamburger Icon Close Icon Sorted

Community and Q&A

Interior and exterior wall design: Comments and concerns

Airfix | Posted in General Questions on

I’m at the point of finalizing my wall design and before I started to pour foundations I thought I’d see if any of the experts here could pick holes in my wall design philosophy.  Attached is a PDF of my plan.

I’m in climate zone 6a.  New construction at 7000ft elevation with walk out basement.  I’m going for a “pretty good house” concept with outie windows

To make it easier for comments here are some specific questions i’m still pondering:

1) I’m showing BIBS cavity insulation but is there any reason I should (or should not) be looking at cellulose.  A builder acquaintance of mine at a Christmas party suggested I should use cellulose as it goes on wet and is a better air seal than BIBS.  I’m worried about the moisture content and drying time.

2) I’ve shown a half inch gap between the basement polyiso and the finished interior slab which is taped.  Should I be concerned about moisture leaking in through the foundation wall, maybe not now but in 10 or 20 years and would you recommend I do anything different than shown here?

3) Because I’ve got a stone veneer that covers the foundation wall and in most cases extends up several feet into the wood framed section AND because I’ve got 2.5″ of polyiso on the house I had trouble deciding how to make the drainage plane behind my siding match up with the drainage plane behind the rock veneer.  In figure 2 you can see that I’ve extended my 2.5″ of exterior polyiso over the outside of my foundation wall.  The WRB is on the outside of the polyiso.  As you can see I have my foundation wall sandwiched between the inside and outside polyiso.  Does anybody see any issue with this or can they recommend a better method of doing this?  I also thought about mounting furring strips to the outside of the concrete, adding a layer of sheathing to that and then the wire mesh and lath and then the Sure Cavity drain then the veneer but thought the foam option seemed better.

4) The whole stone veneer system is supported by 5″ x 5″ x 1/4″ galvanized angle iron.  It will be “floating” about 6″ above finished grade.  Any comments?

5) Figure 3 – I’ve shown a metal bug screen stuffed with a ridge venting material but I’m not sure really how to do this detail and shooting a little bit from the hip.  Does anybody have comments suggestions?

6) Drainage behind the stone veneer will be via a 5mm SureCavity drainage material.  Does anybody have any comments on this material or have any other suggestions for creating the drainage plane behind the stone veneer?

7) Should the WRB extend all the way down to the angle iron or should it stop an inch or two below the top of the foundation wall?

8) Any other suggestions for improvement or concerns?

Cheers,

Steve

GBA Prime

Join the leading community of building science experts

Become a GBA Prime member and get instant access to the latest developments in green building, research, and reports from the field.

Replies

  1. BrianPontolilo | | #1

    Hi Steve,

    Thanks for sharing your drawings. I'll wait to let some of the regulars weigh in on your wall assemblies, but no major problems jump out at me in areas, I am familiar with (I'm not familiar with details for stone veneer.

    Keep in mind that damp-spray cellulose is only one type of cellulose. Maybe it is common in your area, but dense pack cellulose is packed behind netting and is dry when installed. And I'm not sure about the need to hold the insulation 1/2 inch from the slab. If your foundation wall leaks down the road, you're going to have some work to do either way.

    Let's see what the community says about your plan...

  2. Airfix | | #2

    Does anybody else have input on my wall design or feedback on my questions? Martin or Dana or Bueller?

  3. GBA Editor
    Martin Holladay | | #3

    Steve,
    Question 1. Why have you decided to make the top of the foundation wall extend above the level of the interior slab?

    Question 2: Where is exterior grade? I guess you answered that -- 6 inches below the bottom of the stone veneer, I guess -- but I just want to be sure. If the grade is that low, why does the foundation wall stick up so high?

    Comment: Personally, I don't like to see stone veneer floating in mid-air, above grade. If you want to install fake siding that looks as if you are building a stone house, it should be realistic and should extend below grade. Otherwise, the "I've got a stone house" illusion is shattered.

  4. Jon_R | | #4

    Below covers BIBS vs cellulose. Also note that cellulose contains borates, which can be beneficial.

    http://www.mnshi.umn.edu/kb/scale/insulation_densepack.html

  5. Airfix | | #5

    Martin:

    Question 1. Why have you decided to make the top of the foundation wall extend above the level of the interior slab?

    Because our lot is on a 20% to 30% grade and I have a 10 foot foundation wall at the back of the house and it steps down on the sides of the house until at the front of the house (grade level) it stops at the level of the interior slab.

    Question 2: Where is exterior grade? I guess you answered that -- 6 inches below the bottom of the stone veneer, I guess -- but I just want to be sure. If the grade is that low, why does the foundation wall stick up so high?

    You're right in that the contractor will not extend the foundation wall much more than 6" above grade. However there are spots on the side (due to our steep slope) where there is a step in the foundation where the foundation may be partially covered by a retaining wall and partially exposed. I'm accounting for that transition in my sketches.

    In addition my contractor has said he wants to support the stone veneer from angle iron mounted to the concrete. This is how he has done it in the past (granted without exterior foam). Therefore the stone veneer needs to extend over the concrete framing transition. My sketch attempts to handle that transition as gracefully as possible.

    Comment: Personally, I don't like to see stone veneer floating in mid-air, above grade. If you want to install fake siding that looks as if you are building a stone house, it should be realistic and should extend below grade. Otherwise, the "I've got a stone house" illusion is shattered.

    You made this comment on a previous thread and following that comment I drove the town looking at how everyone did their stone/grade transition. What I found is about 50% ran their stone to the ground and 50% had their stone stop about 6" above grade. You're right it looks much better to run the stone to the grade. However when I approached my contractor about it he said he prefers to stop above grade. The reason is that in the freeze thaw cycles we get here combined with the effects of constant snow shoveling he's worried the stone veneer would eventually pop off. That means half my neighbors might have problems and half probably don't. However I don't know if those that have their veneer to grade have problems or not.

    1. Jon_R | | #7

      My guess is that 6" of course, clean gravel would greatly increase the odds of stone veneer extending just below grade holding up.

      Or use 6" of evergreen ground cover to hide the gap.

      1. Airfix | | #9

        Jon,

        So 6" of gravel extending laterally and vertically before grade starts? Basically the back fill is topped with gravel?

        It might be hard to keep that from migrating down the slope over time.

        How would I support the veneer running it all the way to the gravel? Still with galvanized angle iron?

        1. Jon_R | | #10

          Yes, gravel would reduce moisture uptake over more moisture retentive soil. Not my area, but my guess is yes, galvanized angle iron in the gravel.

  6. Airfix | | #6

    Here is a snap shot of the south view of my house

  7. Expert Member
    MALCOLM TAYLOR | | #8

    Steve,

    A few very minor comments.

    - I don't see any advantage to bevelling your slab edge. The foam is covered by your interior stud walls.

    - How are those stud walls fastened to anything at the top? You might consider a layer of plywood as a substrate for the drywall on top of that wall, as it has no where to be fastened where it extends over the foam.

    - The drywall is shown extending behind the foam at the bottom of the exterior walls. That makes the sequence of insulation and drywalling a lot more complex.

    - The bottom of your rain-screen cavity at the rock veneer needs a gap between the trim-board and the flashing that extends over the rock to allow drainage and air circulation. I don't think you need ridge material pushed into the perforated U-flashing but it probably does no harm.

    1. Airfix | | #11

      Malcolm,

      Thanks. All great points.

      - I don't see any advantage to bevelling your sub edge. The foam is covered by your interior stud walls.

      Good point. I'll just run the foundation wall xps foam up to end flush with the concrete slab.

      - How are those stud walls fastened to anything at the top?

      Another good point. I probably should stop them at the top of the foundation wall and mount them through the 1.5 polyiso to the foundation wall. I'll then extend the horizontal piece of polyiso across the top of the 2x4 top plate. Would an exterior corner like this pose any problem for drywalling?

      - The drywall is shown extending behind the foam at the bottom of the exterior walls. That makes the sequence of insulation and drywalling a lot more complex.

      Yup. I'll stop the drywall at the top on the horizontal piece of polyiso.

      - The bottom of your rain-screen cavity at the rock veneer needs a gap between the trim-board and the flashing that extends over the rock to allow drainage and air circulation. I don't think you need ridge material pushed into the perforated U-flashing but it probably does no harm.

      I think you are talking about between the siding and the top of the metal flashing just above the topper stone? It's not clear to see but there is a gap there. This will allow air flow up/down between the siding and the WRB.

      If you are talking about between the topper stone and the bottom of the metal flashing to allow air into the rain screen between the WRB, Sure Cavity drainage matt and lath . That's a good point. I'm not sure how to do that while incorporating a bug screen. I'll have to ponder it.

      I saw that ridge material on another wall detail used in this kind of way. I'm not 100% sure of it's function other than to perhaps keep the metal bug screen from buckling when it is attached to the inside of the siding.

      Cheers,

      Steve

      1. Expert Member
        MALCOLM TAYLOR | | #13

        - Rather than lower the interior wall to the height of the foundation, I'd fasten a 2"x2" to the inside of the bottom plate and secure the two walls together with a piece of 1/2" plywood. The other benefit of this is providing a solid substrate for the drywall ledge. At some point someone (a kid, your helpful brother-in-law) will stand on it, and crack that drywall joint.

        - I try and think about detailing the rain-screen so it stays open over time. To me the best solution is perforated U-flashing that you could blow out with a compressor if it get plugged by debris, or small insects. A good second choice are Cor-a-vent strips. Bug-screen and fuzzy stuff seems a distant third.

        - I'm not sure venting behind the stone is much of a concern. I think your detail looks fine.

        Good luck with your build!

  8. Airfix | | #12

    Any comments on sandwiching my concrete between two pieces of polyiso to provide an extension of the water drainage plane?

    Should the WRB house wrap extend all the way to the angle iron or stop just below the top of the foundation wall?

Log in or create an account to post an answer.

Community

Recent Questions and Replies

  • |
  • |
  • |
  • |