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Choosing wall assembly details

David Burke | Posted in Green Building Techniques on

Hey Advisors,

I’m asking this question for a neighbor. I have my theory but I would like to see what the general advises have to say.

Here’s the building:

located in central VT

double stud wall construction, rough cut 2×4 construction, total wall thickness around 8″

sheathing is diagonal rough cut 1×6

2 stories, full first floor and knee walls on second story

cellulose as bulk insulation

The question:

Looking to air seal this building on the exterior, was offered a spray membrane by the insulator but the technology doesn’t feel right. This product goes on the exterior.

http://www.tremcosealants.com/commercial/products/product_detail.asp?selected_type=1&product_id=298

My suggestion is a highly detailed wrb of “solitex mento 1000”

http://www.foursevenfive.com/index.php?main_page=index&cPath=70_71_98_97_101_73&zenid=kpr0vgv98i20bv1uq88kggl8o2

Then finish the interior with a highly detailed air tight drywall approach without a vapor barrier.

Would solitex mento 1000 provide a big enough improvement in air sealing over typar to warrant ordering it from brooklyn?

My other option, if air sealing is deemed a priority is to spray foam a 2.5″ to 3″ lift on the interior and fill the rest with cellulose. This way typar would be used as the wrb.

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Replies

  1. Aj Builder, Upstate NY Zone 6a | | #1

    Your local expert in VT is Robert Riversong. Google

    Read this GBA blog

    https://www.greenbuildingadvisor.com/blogs/dept/green-building-blog/regional-variations-pretty-good-house

  2. David Burke | | #2

    ahh yes river song. i emailed him a while ago about something else.

  3. Ken Levenson | | #3

    David,
    Great to see your questions regarding our product. Admittedly not impartial here, but I think AJ Builder's link is right on. Resiliency, simplicity, robustness - doesn't matter if we're going for Passive House metrics, we should build to perform in a reliable way. Our experience says the Typar won't provide airtightness. The Solitex Mento 1000 can give you Passive House level airtightness while keeping the enclosure vapor open and waterproof. The waterproofing is delivered by gravity as it should be - taped membrane joints are for the airtightness. And unlike Typar and Tyvek it is truly waterproof too, as it is a monolithic membrane - no tenting. Spray foam is a crap shoot for airtightness and terrible for drying/resiliency. Let the cellulose work its magic and the Solitex membrane keep it from the wind - a great combination. The only thing I might add is that if you want to truly optimize the cellulose you might consider an airtight layer inboard too, eliminating any potential losses due to thermal bypass, such as with DB+ interior membrane - which also offers the bonus of vapor variable retardation. Of course we're happy to discuss details further and help optimize the use of materials and approach - just give us a call at 800-995-6329.

  4. David Burke | | #4

    Ken, thanks for responding. Forums never cease to impress with the direct contact we can get with manufacturers and distributors.

    Can you speak to the relative air permeance of your product vs typar/tyvek?

    I tried to look them up for comparison but was hesitant I would end up with apples to oranges data.

  5. Ken Levenson | | #5

    David,
    Yes, comparisons can be difficult to ascertain. We've written a blog post, that I think you'll find interesting and to the point, on the testing performance of Solitex Mento here: http://www.foursevenfive.com/index.php?main_page=page&id=15&p=1338
    But the very short answer is that generally, so to speak, the Tyvek commercial wrap just meets the American definition of "airtight" per AC38/ASTM E2178 of .004 cfm/ft2 with .001 cfm/ft2. While the Solitex Mento 1000 tests at .00004 cfm/ft2 or 100 times the standard and 25 times Tyvek. The Typar data I'm seeing is listed differently and we'll take a closer look at what it seems to be saying and report back.

  6. GBA Editor
    Martin Holladay | | #6

    David,
    As far as I know, liquid-applied WRBs (like the Tremco product suggested by the contractor) are not designed to be installed on rough-cut 1x6 diagonal board sheathing -- especially if the boards are green lumber. These products are designed to be installed on plywood or OSB. For more information on liquid-applied WRBs, see Housewrap in a Can and New Green Building Products.

    Concerning your second question -- "Would Solitex Mento 1000 provide a big enough improvement in air sealing over Typar to warrant ordering it from Brooklyn? " -- I would answer, "probably." I certainly wouldn't use Typar for an air barrier; I would recommend taped OSB or taped plywood as an exterior air barrier for most homes. If you want to use a fabric as your air barrier, one of the European fabrics will probably perform better than Typar.

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