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Community and Q&A

A wall with EIFS and SIS — What’s the vapor profile?

user-1121214 | Posted in GBA Pro Help on

I need a little help with a wall detail, for a three story house we’re building in Arlington VA, Zone 4a mixed humid.

The lower 2/3 of the wall will be clad with EIFS. The upper 1/3 will be clad with a cementitious shake panel. The two finishes are separated by a water-table/apron like trim detail. 1″ XPS will be continuous over the SIS on 2×6 framing with blown cellulose inclosed with ADA drywall. Cementous shake installed with rain screen, firring strips over XPS, flashed over the water-table trim.

A typical detail would be EIFS over a drain mat over WRB over sheathing. How does replacing the OSB with SIS change the vapor profile? Where should the drain mat be placed and for that matter the WRB?

The roof is a cathedral ceiling framed with trusses giving us 18″ at heal and on slope. Probably blown fiberglass with vents under the sheathing, continuous soffit and ridge vents, asphalt shingles, 4′ overhangs, no ceiling penetrations except surface mounted light boxes. Poured basement walls with continuous internal XPS and 3 1/2″ cellulose in wall cavities.


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  1. wjrobinson | | #1

    Mac, with all do respect, don't go online to completely design a new home. Find out who near you can design and or build what you desire. Michael Chandler, GBA Advisor may be able to help you here the most.

  2. GBA Editor
    Martin Holladay | | #2

    Contact your EIFS supplier. Every EIFS manufacturer I know of has specifications for sheathing and WRB placement. You can't make up these details as you go along -- especially with EIFS.

  3. user-1121214 | | #3

    Wow, I didn't expect to get shoot down so quickly for trying to get some clarification on a wall detail. Maybe I gave to much information or worded my question poorly. I was simply wondering how replacing OSB with a SIS panel would change the vapor profile of a known detail. The one Martin described in his article on stucco, with a drainage mat behind the xps, which is an improvement over the one in the library by Peter Yost with two layers of felt as the drainage plane. Which we have been using for years. I have looked at all the details from two EIFS manufacturers and most details list "an approved substrate" and show wood sheathing in their details. I am waiting for a return call. We are not in construction and I'm not designing as we go, we are in planning, and I am planning on getting the details right to pass on to our crews/subcontractors.

  4. GBA Editor
    Martin Holladay | | #4

    I wasn't shooting you down; I was providing advice. If you've contacted your EIFS supplier, that's great. We both agree that it's a good idea.

    EIFS has suffered plenty of litigation, so if you want a warranty, you have to do exactly what your EIFS supplier says.

  5. user-1121214 | | #5

    Sorry Martin, I read AJ's and your response at the same time and well... I wasn't feeling the love.
    As a builder for almost 30 years I was very happy to find this site and consider it a great resource. I've read many of your articles/blog posts and always find them enjoyable and informative.

  6. wjrobinson | | #6

    Mac, I tried to sound positive and still I agree with Martin, manufacturer details trump the mish mash of online opinions. Glad to see you are a fellow builder. Get ahold of Chandler. He is on the leading edge of all things building in your area.

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