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Another wall-plan-question thread

jklingel | Posted in Energy Efficiency and Durability on

Situation: Fairbanks, Alaska, heating degree days of 14,000. Building a two-story addition onto an existing house, built in ‘80.

Walls will be double-stud, filled w/ dense packed cellulose, 10” to 12” wide. Exterior siding will be T-111, as the boss wants to match the T-111 on the old house. My old walls have a 6 mil poly VB, 13” of ‘glass, then T-111.

Now for the questions:
(1) An inspector said “We only accept 6 mil poly as a VB.” Upon asking, he then said “One perm or less”, but was not familiar w/ ADA. I can fix that. Thus, a poly VB would probably be OK, but I would like to eliminate one. Given my conditions, is ADA advisable instead of poly, or is the ADA and MemBrain perhaps a better alternative? Membrain almost sounds SciFi.

(2) The bigger question is what to do on the outside. The old house has the fiberglass right against the T-111, but reading threads here indicate that I should have a WRB like Typar between the T-111 and the cellulose. If so, obviously the Typar will sit right against the T-111 and may hold liquid water against the plywood, either because of a leak or melting condensation. Too, the plywood is going to get cold; will winter condensation likely be a problem if the T-111 is stained to be vapor permeable?

(1) (a) ADA, or ADA and MemBrain for the inside.
(b) Tenoarm VB on the inside.

(2) For the outside, here are some choices.
(a) 12” of dense-packed cellulose, Typar, then T-111. Optional: Nail 8’ x 1x2s, on edge, on the T-111, one per stud bay. Leave the Typar a tad loose. The 1x2s pushing the Typar in a tad will give a little breathing room. ???

(b) 10” of dense-packed cellulose, 2” of non-foiled EPS, Typar, T-111.

(c) 12” of dense-packed cellulose, 1/2” CDX, Typar, vertical 1/2” strips on the studs, then alum, vinyl or wood siding, and live alone.

(d) Other?

If I have the T-111 two inches from the studs because of EPS, I assume it would be wise to either have plywood sheets, inlet 1x4s, or metal cross bracing at the corners. A stain that is vapor permeable; suggestions there?

Thanks. john

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  1. Riversong | | #1


    I vote for live alone, go fishing all the time (and send me more salmon ;-)

    Second place would be either ADA (if you can keep the indoor RH down below 35% all winter) or poly VB or Membrane for your extreme climate (I doubt you're air conditioning the place), densepack, #15 felt, and then T111 applied directly to the studs to serve as shear bracing.

    Just make sure that horizontal joints in the T111 are either lapped or Z-flashed and integrated with the WRB. I've shifted the gable studs outward 3/4" to allow the gable T111 to lap over the T111 on the wall below (and it breaks up the flat surface).

  2. jklingel | | #2

    I vote for live alone....•• But "She" (the She, who must be obeyed) is a good cook.

    Second place would be either ADA (if you can keep the indoor RH down below 35% all winter)... •• RH in here is typically in the 20's most of the winter. I've had a little meter sitting on a window sill for a couple of yrs, and it does not seem to change much the few times I've moved it inward. I will do better monitoring and may bring the RH up a tad, for health reasons, but not exceed the 35%-40% I keep reading about.

    or poly VB or Membrane for your extreme climate... •• Is the Membrain going to be working in 40 yrs? I know poly will. I'll have to internally debate this; sure would like to eliminate the VB.

    (I doubt you're air conditioning the place)... •• Not a chance.

    #15 felt...•• That keeps popping up as still the #1 WRB, but I was worried about the seams flopping around between studs, and maybe fatiguing. But then, how are they going to flop with no air movement? Never mind that concern. I think Martin once suggested going to 30#, as the felt has gotten thinner over the years. I'll give each a feel. When I put some 15# under roofing last summer, it did seem skimpy.

    Just make sure that horizontal joints in the T111 are either lapped or Z-flashed and integrated with the WRB. I've shifted the gable studs...•• I was planning on bumping the second floor wall out, but thanks for mentioning that. Reading about the innie vs outie vs middle windows, I'll also have to digest that. I see the merits of bringing them in a tad or two. Thanks for the opinions. I wish Membrain had a 50 yr track record already. j

  3. Riversong | | #3


    I wouldn't bet on the poly lasting 50 years either. All plastics lose their plasticizers over time and get brittle. It'll probably last a good long time buried in a wall, but I don't think there's much research into that.

  4. GBA Editor
    Martin Holladay | | #4

    Q. "Given my conditions, is ADA advisable instead of poly?"

    A. Your location -- Fairbanks, Alaska -- is the poster child for interior polyethylene. Your inspector is right: you should use interior polyethylene in your climate.

    Interior polyethylene is a vapor barrier -- but not necessarily an air barrier system. You have many options for creating an air barrier. ADA is one option -- but it's an independent question from the question about poly. You can have poly and ADA.

    Q. "Is MemBrain perhaps a better alternative?"

    A. Save your money. Poly is cheaper than MemBrain.

    Q. "Obviously the Typar will sit right against the T-111 and may hold liquid water against the plywood."

    A. If you are worried about helping the T-111 to dry more quickly -- and I think you are probably overthinking this -- you can always include a rainscreen air space behind your T-111.

    Q. "Will winter condensation likely be a problem if the T-111 is stained to be vapor permeable?"

    A. The T-111 may, indeed, accumulate moisture during the winter. But as long as it dries out every summer, I think you'll be OK.

    Q. "12” of dense-packed cellulose, Typar, then T-111. Optional: Nail 8’ x 1x2s, on edge, on the T-111, one per stud bay. Leave the Typar a tad loose. The 1x2s pushing the Typar in a tad will give a little breathing room. ???"

    A. Sorry, I can't visualize this option. It sounds, however, as if you are suggesting a rainscreen air space. If that's what you are suggesting, it's a good idea.

    Q. "Other?"

    A. There are always other ways.

    Q. "If I have the T-111 two inches from the studs because of EPS, I assume it would be wise to either have plywood sheets, inlet 1x4s, or metal cross bracing at the corners."

    A. Yes. Every wall needs bracing to provide racking resistance. If you are unsure of your plan, talk to an engineer or your local building inspector.

  5. Doug McEvers | | #5

    John, Make sure you prime all sides of the T-111, I prefer oil primer.

  6. jklingel | | #6

    Martin: Thanks. (1) The 1x2's would get screwed to the T-111 "on edge", parallel to the studs. That would keep the Typar pushed away 1.5" in the middle of the stud bay. Yes, I was trying to get a rain screen, of sorts, but not perhaps the best way. I will think less on this one. (2) The question about extra bracing (if rigid foam in used on the outside) was a concern about the nails no longer being in sheer. I will keep the T-111 closer and use something like "krinkle wrap" outside the Typar...???... or a 3/8" air space.

    Doug: OK. Thanks. If I use "krinkle wrap" over the Typar, is an oil stain just as good? I'll be staining the wood instead of painting.

  7. Riversong | | #7

    As is often the case, I'm going to disagree with Martin on several points.

    A poly VB is not necessary in your climate - what's necessary is to minimize vapor diffusion. That can be done by keeping interior RH down with good ventilation and use of point source exhaust fans, and by using any of a number of options to reduce outward vapor flow.

    However, with a thick envelope full of cellulose, it's just as important to allow drying in both directions, so either a low perm element like VR primer or a variable perm element like MemBrain makes much more sense.

    Yes 6 mil poly is cheap, but cheap is not the same as best, particularly in such an important element of envelope function and durability. If the inspector insists on a VB membrane (beyond the 1 perm code requirement), then I would suggest MemBrain since it allows drying.

    A rainscreen behind T111 defeats the purpose of the material, which is to serve as both structural sheathing and siding in one layer. If the interior air barrier is tight and vapor diffusion is controlled, then I would not worry about moisture accumulation in the T111, since - as a single layer cladding - it can dry out more easily than a multi-layer cladding.

    I understand what you've proposed in terms of using 1x2s to deflect the Typar inward between studs to create some breathing room. But that's not a good idea since a WRB should be tight and not allowed to deflect under pressure. If you're concerned about the plastic being in contact with the plywood siding, then - as I suggested - use felt.

    I will also disagree with using oil-based primer. Latex breathes much better. I would, however, reinforce the value of priming all six sides of any wood siding material before installation.

  8. jklingel | | #8

    Robert: Ahh. More info upon which to chew. Man, when I built in '80 I was 3/4 ignorant, but what I did is lasting and functioning well. Getting more educated over the last 30 yrs sometimes leaves me more confused. Decisions were easy when I you didn't know much! I do want to maximize breathing in both directions, as I am absolutely going to be building tighter this time. I will surely skip the idea of the 1x2's, as it does seem to be "over thinking", as Martin suggested. Membrain and ADA will likely be the call; if I run out of money because of the Membrain, I'll have to poach a moose, I guess. Is there any reason to NOT use a "krinkle wrap" over felt? The idea of over-kill appeals to me viscerally. I may even tear off the T111 on the old house and install an external air barrier, as the inside did not get the attention it should have, for various reasons. If the inspector does not like Membrain and ADA, I can avoid him anyway, as I am out of town. I like to build "by code" as much as possible, as you never know if a bank is going to get involved, for me or the next cat. Whatever; I will document it all. Thanks again to all; I'm digesting. john

  9. Riversong | | #9

    Is there any reason to NOT use a "krinkle wrap" over felt?

    YES. Since the siding is also the shear-bracing sheathing, it has to be nailed tight to the framing. No wiggle room allowed.

    If the T111 can breathe and is exposed to the weather for ease of drying, it'll be fine. Keep it at least 8" up off the ground to avoid backsplash and be sure to seal the bottom edge - that's where T111 often rots.

  10. jklingel | | #10

    RR: got it. thanks. j

  11. jklingel | | #11

    BTW: If it were necessary to install 2" of EPS under the T111, I was going to install 1/2" plywood (unless I used metal bracing or inlet 1x4s) on the inside of the outer wall, and figure out how to get the cellulose in there. Not a problem, now.

  12. user-869687 | | #12

    John, about this last point--since you're talking about a deep cavity, I presume this is a double frame. The shear ply should go over the structural frame, if only one is loadbearing. You need to consider how lateral loads are transferred into the foundation, or for a vertically stacked addition, into the lower frame. If the lower level has the T-111 acting as shear bracing and the outer frame bearing, then it makes sense to repeat that at the upper level(s).

    Also consider that the addition will significantly stress the existing lower level, and you may need to add bracing starting at the foundation. The new wall surface will add wind load and extra mass adds to seismic loads. In your area this is enough of a concern that it would be a good idea to consult a structural engineer.

  13. jklingel | | #13

    TJ: I appreciate your time and experienced opinion. I will lay out what my plan is, in a nut shell, and if you have time, voice concerns. The new addition (24'x24') will mimic the old house, but be much more solid. There will be an adequate foundation wall down 4' (10" icf blocks, likely) to a footer, etc, on all four sides, appropriately tied to the existing foundation (via engineer). Slab will float freely. Double wall, w/ the inner one supporting the second floor, the outer one supporting the roof. The second floor subfloor will be extended to tie to the outer wall, as well lots of plywood stickers to join the walls (may even throw in a couple of long, crossed 2x4s). The outside of the inner wall will have metal cross bracing; 1/2" sheet rock on the inside. The outer walls will have T-111 nailed over felt; sheet rock on the inside. The roof will be flat-bottom trusses (flat ceiling, cold attic). New roof will be perpendicular to the old one, and joined up to the old ridge. Common walls will be secured to each other. I assume by "lateral load" you mean wind forces pushing the walls from the side, and that is why I am thinking some long 2x4s between the two would help. And, yes, I am going to have to chat w/ an engineer about all this. Seismic here? 1 Mag >8 every 13 yrs; 1 mag 7-8 every yr; 25 mag 5-7 every yr, etc. I just found that info a week ago. Spooky. Thanks again. john

  14. jklingel | | #14

    " ...outer walls will have T-111 nailed over felt; sheet rock on the inside." Uhhh, ignore that "sheet rock on the inside." Pretty long workout today....

  15. Jesse Thompson | | #15


    Since you're in Fairbanks, why not hire Thorsten Chlupp to consult on your construction methods? He's right in the same town as you and has been working in your specific climate and area for quite some time.

    His new construction methods (post REMOTE) thinks hard about drying directions, affordability, energy use, etc.

  16. homedesign | | #16

    Is "Post Remote" different from what was depicted inThorsten's JLC Article?
    Or the Cold Climate research paper?
    Have you seen something new published?


  17. Jesse Thompson | | #17

    I saw Thorsten present at the Passivhaus conference in the other Portland this fall. He's designing and building passive solar houses for a place that gets no sun for three months of the year. He says he hasn't published anything yet because he doesn't have data for how well the houses are working.

    My notes aren't extensive, but the only foam I remember seeing was below slab, walls were a very thick cellulose larsen truss on 2x frame, ceiling was wood truss w/ deep cellulose. Air barrier on exterior sheathing of 2x frame, well below 0.6 ACH50, walls designed to dry out in both directions (no exterior sheathing on truss). Locally built fiberglass tilt-turn windows with thermal shutters. Masonry fireplace and big flat plate solar thermal array dumping to a water storage tank to try and make it through the dark months, pretty complex heating systems. Energy calculation in PHPP.

    I'm sure he'll publish after he's had a chance to evaluate how well this batch is working, he seems like a very careful person. Described working in a place where climate change is happening quickly right in front of them but people fly in fuel to heat their houses.

  18. jklingel | | #18

    JT. Thanks for that. From a friend of his, Thorsten is currently buried w/ work, but he would be real high on my list of folks to work w/. As soon as possible, I will be getting a copy of what he did w/ his own (I believe it was) house, assuming that that will be public info. He tried to build to PassivHaus specs, and I hope he "publishes" what he did. It is apparently a version of the Larsen/Riversong Truss, full of cellulose. The REMOTE wall is not an option w/ me. I don't like the thing. Too, I am in contact w/ Cold Climate Housing Research Center fairly regularly, and they are very open about sharing what they do/learn. Good group of folks. john

  19. homedesign | | #19

    This is very interesting.
    Thank You.
    I wish Thorsten would keep us posted.

  20. jklingel | | #20

    JT: Your last post was not there when I posted last. You know more about his house than I do. I'm very curious about what his numbers are. j

  21. homedesign | | #21

    Interesting that even Thorsten is following the guy that "some people" are trying to stifle.

  22. Jesse Thompson | | #22

    My impression is Thorsten is too busy with work to be posting on here. And John, please don't add fuel to fires, it's just not helpful to the rest of us.

  23. Riversong | | #23


    Why is stating the obvious truth adding "fuel to fires"? It "ignites" only those who cannot bear the truth.

  24. jklingel | | #24

    JT: Regarding your comment "And John, please don't add fuel to fires...", to which John are you referring? I assume this is in reference to Robert Riversong and his modified LTruss, and John Brooks' comment "...Thorsten is following the guy that...", where I again assume that "following" is meaning "duplicating his system" and not "behind him". Make no mistake about it: John K did not intend to incite anything about anyone. If I was misinterpreted, pls advise. If your comments were for John B, then ignore this. Peace. Klingel. PS: Maybe we need to go by LAST names here, unless, of course, we follow RR's advice and use aliases.... kidding. j

  25. Riversong | | #25

    Funny how it was Jesse's unwarranted comment, and not John B's, that has lit a fire here.

    John K, I think we should use each other's names so no one knows who's saying what and the posts will be judged by the quality of the information rather than as the popularity contest that it is.

    But this is a diversion, which would have been better suited for the New Features thread.

  26. Jesse Thompson | | #26

    I was referring to John Brook's statement: "Interesting that even Thorsten is following the guy that "some people" are trying to stifle." Sorry John Klingel, I should have been more precise, nothing to do with your thread!

  27. Jesse Thompson | | #27

    John K, it was a very impressive presentation, Thorsten's recent projects are extremely ambitious in such a severe climate.

    It's humbling to see what he's doing in a climate with twice the HDD as ours, it makes me want to try harder and not make excuses for living in a cold place.

    Jesse Thompson

  28. jklingel | | #28

    JT: No sweat. I figgered that. From what you said, Thorsten is digging deep, literally. I wonder if some of his "tricks" have a + ROI. Someone has to push the envelope if we are going to learn. RR: So I am more popular? WHEEEE HA! Is Dancing with The Stars next? (I think we are getting off topic here....). Klingel

  29. Jesse Thompson | | #29

    John B, I should clarify what I meant by "adding fuel to the fire".

    I don't know what sources Thorsten follows, or who he is in private conversation with, or what he has based his wall system on. I saw a 30 minute presentation with photos of two of his recent houses, and I think there was a wall section displayed, but I honestly don't remember, it was part of three fast moving presentations during one session (including Tim Eian's recent passivhaus and a 300 sf passivhaus in Seattle by Joe Giampietro).

    Hopefully PHIUS will post the proceedings of the conference like they have done in past years, and we'll be able to learn more details about what he's up to without relying on my faulty memory.

    So, in my opinion, to imply that Thorsten's projects are a result of any single person's technical achievements or to link his projects to this website's social soap opera is inappropriate, and he wouldn't appreciate being dragged into it.

    Those were my thoughts at the time, sorry if any offense was taken.

    Jesse Thompson

  30. homedesign | | #30

    My apologies to Jesse, Thorsten & John Klingel

  31. jklingel | | #31

    JB: I'm cool, man, but thanks for thinking of me. klingel

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