[Greenbuilding] Insulation Problems

[J Messerschmidt]

Alan,
That's not a bad idea.  I think it's fair to say that the insulation value is being reduced from R10 to what, an R6 - due to the heat transfer of the metal bars.  I think the key is whether we can safely tape the joints to provide continuous insulation, while allowing drying to the outside.  What's your opinion on that?

Thanks!

John




----- Original Message ----- 
  From: Alan Abrams 
  To: J Messerschmidt 
  Cc: Thomas Lewis ; greenbuilding at lists.bioenergylists.org 
  Sent: Thursday, November 11, 2010 11:23 AM
  Subject: Re: [Greenbuilding] Insulation Problems


  building on John S's comments...

  ...are there some semi rigid strips of something like neoprene that could be applied over the outside face of the z-bars, that would have sufficient resistance to compression to support the cladding yet still provide some thermal breakage before the cladding is attached?  this assumes that the potential for heat loss through the bridges is so great that even the addition of R-0.5 btwn bars and cladding would be significant.


  AA



  Alan Abrams
  Abrams Design Build LLC
  A sustainable approach to beautiful space
  alan at abramsdesignbuild.com
  www.abramsdesignbuild.com
  202-726-5894 o
  202-437-8583 c
  202-291-0626 f





  On Thu, Nov 11, 2010 at 11:02 AM, J Messerschmidt <John at fourpointscg.com> wrote:

    Hi Thomas,
    I love the suggestion of taping the seams and taping the board to z bars.  With the air leakage to the outside eliminated that would bring us a lot closer to the r-10, and it would be a proper drainage plane.  My concerns are, what kind of tape and how does water escape if it does get in?  2" of xps has permeance of .55.  Will that allow vapor  to escape? What about bulk moisture?  Behind the xps is a liquid applied membrane that probably has a very low permeance, so it has to dry to the outside.  

    Lastly, looking at the interior wall assembly, if the open cell foam has a perm rating of 8, and 1" of polyiso has a perm of 2.33, this could be a well insulated wall and will still dry to the inside.  Right?  Unless I'm missing something, we'd end up with about an R30 wall.  I'd be very happy with that.  What do you think?  


    Thanks!

    John



-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.bioenergylists.org/pipermail/greenbuilding_lists.bioenergylists.org/attachments/20101111/49e92426/attachment.html>