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  1. #1
    Join Date
    Jul 2004
    Location
    Midwest
    Posts
    52

    Default Is this a better wall detail?

    I'm seeking a good and better wall detail to improve production homes built in the Chicagoland suburbs in the 60s and 70s. These are working class suburbs where deep energy retrofits aren't practical. The mechanical systems are usually aged 80% efficiency systemes.

    Please see attachment. In general, the stud walls have fiberglass insulation with Kraft facing toward the inside. The exterior has asphalt impregnated fiberboard sheathing, fiberboard siding which has been covered with fanfold insulation and vinyl siding. Insulation shows signs of air infiltration and water infiltration around the windows.

    For a siding and window retrofit "good" solution I spec adding Tyvek to the existing fanfold insulation and adding window/door flashing. Is the "better" solution to remove the existing fiberboard siding? There is existing let-in bracing in the corners, but does the fiberboard siding provide additional racking resistance. What are the benefits of removing this siding?

    The basement brick veneer /stud knee walls have no weeps or ventilation and the intended air gap is filled with mortar droppings. The asphalt impregnated sheathing behind these brick knee walls is usually decomposed along the bottom. The rest of the sheathing is usually in good shape with limited signs of condensation. Will adding XPS insulation in these stud bays fill the degraded void and improve the situation or am I trapping moisture? Also, will adding XPS insulation to the poured foundation walls cause frost heave? For years these walls have been warmed by the escaping heat.

    Most basements have limited sump functionality but are relatively dry with patches of mold/mildew along exterior floor/wall intersections. Will my floor details allow for drying or again, am I creating a worse condition?

    Your feedback is appreciated. Thanks! Amy
    Attached Files Attached Files

  2. #2
    Join Date
    Aug 2009
    Location
    OrangeCounty California.
    Posts
    152

    Default Re: Is this a better wall detail?

    It is just my opinion but I think you would be better to attach the Tyvek to the fiberboard, replace the fiberboard siding with 3/8" furring strips run vertically on the studs to give the exterior part of the wall a way to drain any possible water infiltration. Then re-apply the vinyl siding.
    Use a brick cap flashing that will attach 2.5" or more to the studs (higher) behind the sheathing and keep the siding material min. 3/4" above the brick.
    This is all somewhat off-hand as I have not done a lot of design work in your area.
    I think that the fiberboard sheathing is not providing any appreciable shear value.

    Andy.
    Was a GC, doing drafting & design now.
    www.draftinginoc.com

  3. #3
    Join Date
    Nov 2004
    Location
    Boston, MA
    Posts
    4,732

    Default Re: Is this a better wall detail?

    I would forget the walls until you air seal and insulate the attic. They are production homes with conditioned basements?
    "First we finish the game, then we’ll deal with the Armada!"

    Sir Frances Drake

  4. #4
    Join Date
    Jun 2004
    Location
    Des Moines, Iowa
    Posts
    3,817

    Default Re: Is this a better wall detail?

    Amy

    I do a lot of moisture intrusion consulting work and remediation.

    I think the best is to remove everything down to the wall sheathing and start over. This way you can assess how bad the damage is and do what it takes to seal around the windows to prevent further damage.

    Ted got in here ahead of me but he has a good point.
    Mark Parlee
    BESI(building envelope science institute) Envelope Inspector
    EDI Certified EIFS Inspector/Moisture Analyst/Quality Control/Building Envelope II
    Level one thermagrapher (Snell Training)
    www.thebuildingconsultant.com
    www.parleebuilders.com
    You build to code, code is the minimum to pass this test. Congratulations your grade is a D-

  5. #5
    Join Date
    Jul 2004
    Location
    Midwest
    Posts
    52

    Default Re: Is this a better wall detail?

    Andy, Ted, and Mark -Thanks for your replies.

    Most of these homes are split levels, so not true basements ~ 4' below grade and 4' knee walls with attached garages at grade level. And yes, everything is finished. As far as airsealing the attics, that is an excellent suggestion. But, most soffits are not vented although there are ridge vents. Oddly enough, most roofs look okay (with the exception of ranches with crawls - but I cannot tackle all this at once).

    When you say remove down to wall sheathing, do you think it is best to leave the fiberboard sheathing and build from there. In this case, would the next layer be a WRB and then vinyl siding? Does the let in bracing provide enough strength?

    Regarding the brick knee walls, if I butt up the XPS adjacent to the existing blackboard inside the stud bay on the basement brick knee walls, would the solar driven moisture still be able to dry to the inside? Do I want it to?

    There are so many issues to address at once. I'm looking to prioritize and create better, long term healthy environments. Thanks again for your thoughts.

  6. #6
    Join Date
    Jun 2004
    Location
    Des Moines, Iowa
    Posts
    3,817

    Default Re: Is this a better wall detail?

    The let in brace does provide strength against racking. The interior drywall adds to this and everything works in concert to give strength in the assembly.
    WE have a bunch of three story apartment buildings with one inch foam as the wall sheathing and metal braces. The exterior wall are 24" O.C. I never really thought much of this design but it does work.

    The reason I say strip it to the sheathing is that I see so much hidden damage caused by moisture intrusion and you will not know until it is stripped.

    The next layer would be the WRB, installed in a very detail conscious method. Properly lapped and taped to drain all incidental moisture back out from behind the siding.

    The brick detail deserves more discussion than I have time to give it this morning.
    Mark Parlee
    BESI(building envelope science institute) Envelope Inspector
    EDI Certified EIFS Inspector/Moisture Analyst/Quality Control/Building Envelope II
    Level one thermagrapher (Snell Training)
    www.thebuildingconsultant.com
    www.parleebuilders.com
    You build to code, code is the minimum to pass this test. Congratulations your grade is a D-

  7. #7
    Join Date
    Jul 2004
    Location
    Midwest
    Posts
    52

    Default Re: Is this a better wall detail?

    Taking off the siding is a good idea, but at this point, wouldn't it be better to go ahead and remove the asphalt impregnated sheathing as well?

    I've looked at Joe Lstiburek's Building Science info, so it seems that the existing wall was designed as a flow through assembly. With everything removed to the 2x4 studs, the wall would have a fiberglass batt with facing to the inside. It concerns me that 40 year old homes have many layers of paint, possibly oil based and vinyl wallpaper.

    Any thoughts? Does the assembly need to remain flow through?

  8. #8
    Join Date
    Jul 2006
    Location
    Portland, OR
    Posts
    2,424

    Default Re: Is this a better wall detail?

    They can take off the sheathing easier than they can leave it on. They will just start ripping things off of the studs with a roofing spud. So take it down to the studs

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