Ice and Wat3r Shield as a water Air Vapor barrier with ext insulation
user-7593370
| Posted in Energy Efficiency and Durability on
I am building a “perfect wall” house – 6 inch studs with high density cellulose, sheathing, OSB, 6″ of exterior Rockwool and a rainscreen with wood siding. We are considering using Ice and Water Shield as the Air -Water-Vapor Barrier on the outside of the sheathing at walls and roof. Anyone have any experience with Ice and water shield used like this this?
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I'm assuming you're located in a cold climate. The Cold Climate Housing Research Center in Alaska has done a lot of work with "perfect wall" variants for a variety of climates in Alaska. Look at their work on REMOTE houses.
Also, Building Science Corp has a BSI-096 article that does what you're trying to do. Water and Ice could be used on the sheathing, along with a number of other options referenced in the article. There are a lot of details to consider in addition to your WRB that are discussed. It might be a jumping off point, depending on how far along you are with your design.
I used the REMOTE system when building an addition to my house with plans to renovate the existing house similarly. I used 2x6 studs with batt insulation, osb, peel-and-stick ice and water and 3" of XPS. I used a cheaper peel-and-stick, as it spec'd out fine.
Now, as I am into the renovation, I have changed to ZIP sheathing as my water/air barrier, as attaching all of the peel-and-stick was a pain. I'm a little leery of the attachment of the flashings to the ZIP, but it seems like the XPS provides plenty of water protection.
I couldn't tell for sure if your sheathing was going to be inside of our outside of the exterior insulation. Remember you are supposed to put the WRB outside the insulation to prevent air infiltration from wrecking the R value. I haven't figured out my roof exactly yet but I've currently got my walls at 2x6 with rockwool batts, air sealed plywood sheathing, 2" exterior rockwool, WRB , siding. I'm climate zone 6B.
qofmiwok,
Research on wind-washing seems to show it has very little effect on the R-value of insulation, especially board types.
Interesting, thanks. Do you have a source?
https://www.rdh.com/wp-content/uploads/2017/10/Van-Straaten-Windwashing.pdf
See tables 8 and 9.
I was surprised too. It seems like it has consequences not only for the recommendation that they be protected by a WRB, but also that air-tight baffles are useful in cathedral ceilings, and air-sealing needs to be done between rafters or trusses at the wall/roof intersection.
Your proposed wall assembly seems like a good mix of performance and build-ability. 6" of exterior rock wool sounds difficult to me.
Wouldn't a vapor closed WRB like Ice&Water placed outboard of the insulation be a big no-no: a condensing surface for vapor that has made it's way between cracks in the foam?
Based on the assembly listed order by the OP, I believe it's a mid-wall air/vapor barrier under consideration, with 6" insulation on either side. Should work almost anywhere.
I would recommend an ice & water that will essentially 'gasket' the screw penetrations airtight -- not all the cheap thin ones do this, unfortunately.
Jason, I agree re the OP. I was referring to qofmiwok's notion (comment #3).
Thanks to all for your advice.
Yes the Ice and Water shield WRB is outside the sheathing. Insulation is both inside and outside the WRB layer. Computer modeling suggests that water condensation inside the inner layer should not be a problem.
I had originally specified a Henry vapor closed barrier, but the contractor would prefer to use the ice and water shield with the expectation that it will not require a primer in a cold weather application.
Sealing at penetrations if a plus of the this approach
6"" of exterior Rockwool is a challenge but others have successfully don't this before. But yes detailing at windows gets more complicated