Still not 100% clear
I have been studying high-r walls as well as air barriers and vapor retarders in an effort to design/specify a high-r wall that will perform well in CT (Zone 5). I have now spent many hours reading blogs and case studies etc. regarding these subject matters. I have some solid ideas and have learned a lot about high-r wall construction. Currently, I plan to specify 2×6 studs at 24”o.c. with fiberglass or cellulous insulation in the cavity. The horizontal cement board siding will be fastened through vertical furring then through the rigid insulation, and into the stud beyond creating a drainage plane or rain screen. The interior will be finished with an air tight gypsum approach (caulk etc.). However, due to some conflicting information and/or vague descriptions/details I still have a number of unanswered questions/concerns as follows:
1. Based on my readings, I have a concern about the shrinkage of rigid insulation and the longevity of the adhesive on tapes therefore, I am considerng useing Tyvek or some other wrap in addition to the exterior rigid insulation however, it is not clear to me where the Tyvek should be placed. Should it be on the inside or the outside of the rigid insulation? Again, Zone 5.
2. I am aware of a liquid applied product used under synth. Stucco(EIFS) that is supposedly a drainage plain, an air barrier, and vapor retarder all in one. I believe it comes in two different levels of permeability. I am curious to know why this product is not a more popular method in other non- synth stucco assemblies that use exterior rigid insulation such as the assembly I discribed above and why more people don’t consider using this under siding as it “seams” (pun intended) superior to wraps with tape.
3. I have read pros and cons regarding EPS, XPS, and PIC. Faced and un-faced. Unfortunately, I still don’t know what the best choice of rigid is for this application. Is there an ideal product/perm value for the rigid insulation in this application? Should it be faced or un-faced? (Thus far, I assume un-faced as there is a code requirement for an interior vapor “barrier” and I don’t want to create a double barrier however, some of the recent projects highlighted at building science.com are using two (2) layers of foil-faced rigid insulation (habitat in MA I think)???
4. I also understand the benifit of keeping the dew point outside of the structure but, how much r-value must be outside of the structure in order to achieve this in zone 5? I have read conflicting information on this matter.
5. The whole discussion of vapor barriers is somewhat frustrating as it seems that some of the leading experts at least partially disagree with each other. I understand the concept of drying to the inside and the outside. I understand the negative effects of a double vapor barrier. I am also aware of the code requirements for an interior vapor “barrier” in zone 5. IF… the exterior rigid insulation provides enough r-value to get the dew point out of the structure, should I go with NO interior vapor barrier (against code), a Class II (kraft paper), or a Class III (latex paint) on the interior?
I apologize if some of these questions have been answered previously however; I have been unable to find direct answers to these questions/concerns. Any direct answers that can be given would be greatly appreciated. Thank you.
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