Huber’s Zip System R Sheathing
I just head a long conversation with the Tech Advisors at Huber, the maker of the Zip Panel Systems. They’ve come out with a the Zip System R Sheathing which incorporates the Zip panel with 1/2” (R3.6) or 1” (R6.6) Polyiso installed between the OSB and the stud in one application (see pic#1); available only in TX and PA, but it’ll be soon everywhere else later. It’s a great application and solution for thermal bridging with less labor costs; however, it does come with some issues that must be address by the designer, builder and framer.
1. They are working on the testing and certification of this panel for structural uplift and shear, and they expect to have that done in the next six months or so.
2. You must use typical ½” plywood, “T” metal, 1×4 or Engineered ties to brace your walls.
3. If you are doing advanced framing techniques: a. two stud corners require additional stud on the out wall to be able to nail the next panel.
So, in case you are able to use this panel, be aware that you must address these other points. Their files are pretty big to upload, but you can get them by calling their Tech Advisors at 800.933.9220
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Replies
Armando,
It sounds a little bit like Dow SIS (structural insulated sheathing). Clearly manufacturers are starting to develop products to meet new code requirements for high-R walls and better solutions to thermal bridging.
Yes, I do think several companies will be going that way, but until they address the issue of structural board, it would have limited use. An interesting observation; I had a client comment that he would rather have the taped foam on the outside of the OSB/Plywood forming a moisture barrier and protecting the wood sheathing.
Armando,
The polyiso is not foil faced... Correct?
I don't think so, Albert... I've not seen the product yet, but talking to the Huber Tech. it does have a "backer" so they can glue it to the OSB board, and by the picture it looks like it has a backer on both sides. The local rep is getting me a sample... I'll keep you posted.
Thanks Armando,
I'm really pretty curious about it. I see the attraction to the application of thermally breaking the sheeting, but if the polyiso, or it's facing is not permeable, isn't this just going to trap moisture in the OSB? As I understand it, the exterior membrane applied to the OSB to create the ZIP Panel is not permeable.
It seems to me that the panel will have the ability to draw moisture in at the penetrations of fasteners, R/O cutouts and such, but not have the ability to dry through either of the faces. It would seem that this would keep moisture trapped in the OSB itself and that degradation would begin immediately.
Was there any talk about this? I know smarter (and higher paid) people than me have been developing this, so I'm expecting that this has been a topic during development.
Albert,
I'm glad you noticed that issue... usually I would have seen it, but I guess it did not registered with me... I'll talk to them next week. I'll let you know. Thanks.
Albert
I have done a lot of research on the ZIP product and have also spoken directly with their building scientists and developers. The green coating is in fact permeable, to the degree of 2-3 if I remember correctly (I have the info saved on my work computer at my firm so I can not verify). They also claim the nail penetrations, assuming it is installed correctly, do not allow any additional perm or air infiltration.
This looks like an interesting product however.
Thanks Jesse,
It would be interesting to see what you have on it. That the standard ZIP panel is more permeable than OSB is contrary to what I've found and read so far. My understanding was that the added lamination of the membrane and associated adhesive lowers the permeability to near zero. I don't know what the actual number is and I don't know anybody that knows what the actual number is.
Perhaps I'm missing it, but after checking again this morning I can not find a statement on the Huber website that states what a panels permeance is.
The reason that I'm interested is that when I think of OSB, I think of it as drawing water (liquid) up it's cell walls just like a straw until it's saturated. It would seem that the linear orientation of the strands would allow that to happen at any penetration or cut in the panel that is exposed to liquid water, and to a lesser degree, water vapor.
The whole idea with the ZIP panel is that it has a WRB laminated directly to it. If water gets behind the laminated WRB, then it can dry out the backside of the OSB. I would think that it's worrisome that if the laminated membrane on the face is vapor closed (as is the huber tape) and now the backside has an impermeable pollyiso lamination on it, then liquid water absorbed will have a really hard time drying it's way out.
Of what I saw here, ZIP panels permeance is around 12 to 16 perms. http://www.zipsystem.com/uploads/file/JLC%201-28508325%20Final%20eprint.pdf
Correct me if I am wrong, but the biggest problem (at least in cold climates) is the limit 1" polyiso. As often discussed here on GBA (and totally right) you need quite a bit of foam on the outside to make these assemblies work. Once you installed your 3-6 inch of foam on the outside we can worry about the permeability of the WRB. We have to look at the perm ratings of all layers as also recently discussed by BSC (http://www.buildingscience.com/documents/reports/rr-1101-influence-low-permeance-vapor-barriers-roof-wall-performance/view). In Germany we use a quite simple, stationary model ("Glaser diagramm") that gives you a good idea about the hygrothermal performance of assemblies. In doubt use WUFI.
Marc, Thanks very much! I had heard that the overly had a high permeability and could never seem to find a rating for the assembly. One would guess that since the overlay is in the 12 to 16 range, it will allow moisture in the panel to dry out the face.
Phillip, yes I agree wholeheartedly. A panel like this is a real problem without significant exterior insulation. With your apparent experience with building styles in Germany, What are your thoughts about the high perm exterior sheeting used over there and made by Agepan, Steico and the others? Do you agree that maintaining an incrementally higher permeance from the insulation cavity out, negates the need to keep the sheathing warm? That this approach allows one to use an high r values dense pack assembly with confidence?
Albert,
High-permeance sheathing may mean that it isn't necessary to keep the sheathing warm in winter. But it raises a new problem: addressing inward solar vapor drive, which can be problematic if the building is air conditioned.
Martin,
Well yes certainly. Isn't that the point of the vapor control layer at or near the drywall layer? I'm speaking in the case of a heating climate and considering a vapor control layer as: Taped OSB, Plywood, Membrain, SIGA Majpell and the like. Do you agree with this?
Btw... stay above water and out of the wind...
Albert and Martin,
I am positive that assemblies with a high-permeance sheathing work if done right. I do see the problematic with the inward solar vapor drive with air conditioned buildings. If AC is needed in the summer you basically deal with a somehow mixed climate (not so much in Germany). However the stationary hygrothermal analyses I do, looks at the summer conditions as well. I live in MN where most buildings have AC but winter definitely rules. Here approx. 9 month out of a year the vapor drive is outward and 3 month inward. From a hygrothermal standpoint there are two types of wood walls In Germany: diffusion open (here often referred to the breathing wall) and diffusion closed (using vapor barriers). Both work well in Germany. My personal preference is the diffusion open one using the inner sheathing (mostly OSB) as a vapor retarder and a permeable outer sheathing (e.g. the products you pointed out or dense glass). I am convinced that this works here in MN as long as you do a rainscreen, use cellulose for insulation and tape the joints of your permeable housewrap.
Albert,
A vapor-control layer behind the drywall is not the best solution to this problem. If you choose 6-mil poly, you'll end up with a lot of water on your bottom plates. If you choose MemBrain, as you suggest, you'll probably be OK.
More important details include a ventilated rainscreen gap between the siding and the sheathing, and, in some cases, rigid foam sheathing.
Martin,
Agreed. 6mil poly is bad. :(
In my understanding 7/16" OSB, 1/2" plywood, Membrain, Majpell all have a perm rating above 0.5 and below 1 perm (with the exception of Membrains advertised variable perm capabilities). And that this range is in a reasonable range to balance both inward and outward vapor drives in a heating climate. What I continue to hear is that a diffusion open wall in this case has a ratio of at least 10 to 1 in increasing permeability starting at the inner vapor control layer (of less than 1) to the final exterior layer of a perm rating greater than 10 (behind a rainscreen of course!).
My issue with this is the one inch clear that the nail is unsupported between the sheathing and the stud. I want my sheathing to be directly and securely fastened to the studs and plates and mud sill for storm bracing ( flying trees ) Having the foam on the outside of the sheathing makes the connection to the studs better when loaded in shear and allows the force of a tree falling on the rake to be transferred in the sheathing layer to the mud-sill.
Jesse,
I think they are giving the perm rating of the WRB only and not the whole panel. OSB has a perm rating between 1 and 2 so it would be surprising if the whole panel now has 12-14 unless they developed a new OSB too!? Once again it is not only about the perm rating of the inside and outside layer but rather every layer of the assembly should be considered.
Philipp
Yes, I mistyped. The perm rating of the green ZIP covering is 12-14. But the overall rating is basically the same as standard OSB sheathing. Basically, what it comes down to is ZIP sheathing is infact not less permeable then OSB, like some people on this board has mentioned with cautioning about trapping moisture.
All: I looked up my information today from Huber, Manager of Building Science, Danko Davidovic , PhD and he states the perm rating of the ZIP covering on the OSB panel is 12-14, fyi. However the overall panel perm rating is the same as typical OSB sheathing. -edited with corrections
Jesse,
Thanks for correcting me. Indeed the article was referring to the "overlay" while I mistakenly assume it was for the whole board.
Hello all! New to the board here and trying determine which is the best solution for our next home that will be building in N. Michigan. A little background: we built our current home 5 years ago using PU SIPs (R24) and have large energy heels on our trusses and have about R60 in the attic (blown cellulose). The downside for the SIPs is modifying the exterior walls with small changes you want after living in the space for a couple years (ie adding additional door openings or windows).
We are currently planning the next home and will be going with 2x6 pre-built wall panels. Our plan was to insulate the entire wall cavity with Spray Foam (leaning towards PU again for R value in N. Michigan). The truss company that we plan to use currently offers the wall panels with OSB or with Dow SIS. It appears that the SIS are a good fit for our plan and will provide a complete thermal break on the exterior (1") but wondered if the "green" community knows something that we don't in this regard? Also if we fill the complete bay with SPF do we really need to worry about any vapor barrier?
Paul, this would probably have been better as a new thread rather than tacked on to the Zip system discussion as Dow SIS is a different approach entirely. FWIW we have used the Dow product on a couple of projects where it has performed well, one with a stucco finish and the other using Hardiplank with a rainscreen detail. However we are in N. Carolina and your requirements in Michigan will be different - I think you will probably be OK with spray foam stud fill but with other stud cavity insulation materials the 1" SIS will probably be insufficient.
James,
Thanks for the response. I guess I forgot to ask if this new Zip R Sheathing has more advantages than the SIS material. We would like to have a thermal break on the entire exterior and it seems that both products will do this. The truss company has never worked with Zip but they are not opposed to it.
I was starting to get confused with everyone talking about moisture concerns with the SIS product in cold climates since I could not see how using the SIS with SPF would be any different (besides extra interior osb layer and added bracing) than a PU SIP panel. I guess that is was my main worry, but if using a 2x6 wall with SIS or ZIP R will function perfectly with SPF then I have no worries.
Back to ZIP R vs. SIS
We plan to use a few exterior materials: Fiber Cement planks, cedar planks, stone veneer, and potentially some areas with cedar shake. Now with this better understanding, does one sheathing have an advantage of the other or will we need to create a rain screen on either?
Paul,
Relevant facts:
1. Huber Zip sheathing has no R-value -- it's just a special type of OSB.
2. One-inch-thick SIS has an R-value of only R-5.5.
3. Northern Michigan is in climate zone 6, so for a 2x6 wall with insulated sheathing, the insulated sheathing should have a minimum R-value of R-11.25. For more information, see Calculating the Minimum Thickness of Rigid Foam Sheathing. That means that 1 inch of SIS isn't thick enough.
Martin, Zip System R Sheathing may not be suitable for N. Michigan...
but why do you say it has no R value?
http://www.zipsystem.com/zip-system/rsheat.aspx
John,
Thanks for the correction -- I was thinking of Zip sheathing, not Zip R Sheathing. I didn't bother to re-read this old thread -- my sloppiness.
Martin,
I guess I am still confused after reading the article you linked to on exterior sheathing. If using 1" SIS and filling the interior cavity 100% with PU Spray foam (either 2x4 or 2x6 wall cavity), how is this any different than a SIP installation? I am looking for the best sheathing system to provide the best performance and the best insulation method as well for heating/cooling.
Is the condensation concerns due to the close cell foam (SIS and SPF)? I had just read about the double wall and truss wall construction, do those "breathe" better? What I remember when building our current home is that air-tight was the most important aspect hence why SPF is my top choice and then the sheathing system (Zip or SIS) where the joints are taped take that to the next level.
My head is spinning trying to absorb all this information. What system would you recommend for my zone? We will have a lot of windows so they will be the weak link in the wall insulation maybe I should look at 2x4 with SPF instead of 2x6 given that fact.
Paul,
It's clear that I was posting comments hastily yesterday. Sorry.
You're right, Paul -- if the studs are filled with spray foam insulation, not fiberglass or cellulose, then you don't have to worry about moisture accumulation in the wall sheathing. Thin foam sheathing will therefore be OK.
Martin,
Thanks for the clarification. I thought I was losing my mind trying to figure out how SIPs were ok but the SIS with full SPF wall cavities would not. Just to be 100% clear - is this also the same with ZIP for sheathing? I am now reading up on Advanced Framing (2x6) since we are still in the design stage and it should be easy enough to plan around the 2' layout and using SPF instead of a double wall construction with dense pack cellulose to meet out energy and budget needs. I guess my question is whether to use Dow SIS or ZIP or plywood for the exterior sheathing. The plywood or ZIP would have the advantage of being a nail base but if I use those can I still add just 1" of foam to the exterior without worry of condensation or should the zip or plywood be left uninsulated? Trying to get the thermal break if possible but since we are going to have a ton of windows they will be the weak spot anyways for the walls so it may not matter. I am thinking that having a nail base with a rain screen may be the best for speed of installation while also allowing for ventilation. Your comments are greatly appreciated.