[GSBN] Window Detailing Question

Tue Nov 20 16:02:42 UTC 2012

Mark,

You have certainly sparked a very interesting discussion on one of the more difficult issues of strawbale construction and have found passion in very differing points of view.

However, I think the answer to your basic question of heat loss is that it does not matter where the window is within the depth of the bale as heat transfer starts on one edge of the window/bale interface, travels through the bale around the depth of the window (as well as through the window of course) and then out of the bale on the other side of the window frame. The insulative value of that portion of bale is the same whether it is outer, center or inner.

Now, a window set to the outside leaves a larger segment of the bale exposed to interior temperatures and one set to the inside leaves a larger segment exposed to the exterior temperatures, so that can be a factor depending on which direction the heat is flowing i.e., in during hot summer or out during cold winter.

Thanks,

Danny Buck
President, Daniel Buck Construction, Inc.
Santa Fe, NM

  ----- Original Message ----- 
  From: nature boy<mailto:moontrout at yahoo.com> 
  To: Global Straw Building Network<mailto:GSBN at sustainablesources.com> 
  Cc: Patrick Donaldson<mailto:Patrick at communitecture.net> 
  Sent: Monday, November 19, 2012 6:25 PM
  Subject: [GSBN] Window Detailing Question

  Hi Folks,

  Mark Lakeman at communitecture and City Repair in Portland here. 

  We have a new bale project coming in and we're thinking in terms of some 

  passive haus - kinda design concerns as well. Can anyone please comment 

  on the question below, please?

  - So, we're thinking of bringing the windows of this building inboard to the middle of 

  the thickness of the wall, as opposed to how we normally set them at the exterior edge 

  of the wall. The idea is that we will provide more thermal resistance through the wall at 

  the jamb, head, and sill in order to transfer through more fiber rather than just being 

  able to nip diagonally through the wall around the window frames.

  Is it worth doing this in consideration of potentially increased water infiltration issues?
  Please advise!

  Thanks always, 

  Mark

  Mark Lakeman

  Co-Founder                            Principal & Design Lead    
  The City Repair Project     communitecture, inc.
  Portland, Oregon                   Architecture & Planning
  503-381-5885                        503-230-1293
  www.cityrepair.org                 www.communitecture.net

------------------------------------------------------------------------------
  From: Chris Magwood <chris at endeavourcentre.org>
  To: Global Straw Building Network <GSBN at sustainablesources.com> 
  Sent: Tuesday, November 13, 2012 4:13 AM
  Subject: [GSBN] Can bale buildings be air tight?

  Hi all!

  Maybe the question of whether or not a bale building can be built air tight hasn't been keeping you all awake at night, but it's caused Jen and I some long evenings of thought and lots of detail drawings on our plans! Maybe that's just what keeps northerners warm at night...

  We've been honing in on good results over the past couple of years, and this year we finally nailed it (but didn't put a nail through it... that would have been counter-productive). We just did a blower door test on our most recent project and ended up with a result of 0.99 ACH50. That's approaching the PassiveHaus goal of 0.6, and we realized after the test that we hadn't covered up the open sump pit in the basement, so we may actually get to PH levels with the final test.

  The building has a mix of site-built, clay plastered walls and prefabricated, lime/cement plastered walls. We've long used a system that uses a flexible air barrier (house-wrap type membrane) at the edges of the walls where the plaster will meet ceiling, floor and intersecting walls. The membrane wraps down behind the plaster by 3-4 inches. What was interesting with this building was to find that in some areas that detail worked very well, and in others it didn't help much at all.

  What this tells us is that unprotected plastered edges leak... a lot! Our first blower test helped us discover that some of these seams were leaky. One leaky wall accounted for a shocking 74 square inches of leakage! By eye, it just looked like  the usual plaster shrinkage around the edge of the wall, maybe 1/8 inch. But multiply that around an entire home and it's no wonder that many bale buildings under perform in blower door tests. You can see photos of these areas on our project blog at http://endeavourcentre.org/2012/11/blower-door-test-1/

  What we don't know is why some areas stayed tight and others didn't. Our best guess is that it can come down to quality of work. How long was the barrier tail left? How well was the mesh installed over it? How vigorously was the plaster pushed into the mesh? The plaster pulling away at the edge as it shrinks also seems to cause some slight bending of the skin inward, taking it away from the barrier.

  One good take-away from this project is about the beauty of clay plasters. The leaky edges of the clay plastered walls were relatively easy to address... moisten the edges a bit and squeeze in more clay mix. Everything bonds together and the seams went from very leaky to completely tight!

  Now, if anybody happens to ask if them there bale houses can be air tight, it's possible to answer yes.

  Cheers,

  Chris

  -- Chris Magwood
  Director, Endeavour Centre
  www.endeavourcentre.org<http://www.endeavourcentre.org/>

  _______________________________________________
  GSBN mailing list
  GSBN at sustainablesources.com<mailto:GSBN at sustainablesources.com>
  http://sustainablesources.com/mailman/listinfo.cgi/GSBN

  _______________________________________________
  GSBN mailing list
  GSBN at sustainablesources.com
  http://sustainablesources.com/mailman/listinfo.cgi/GSBN
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.sustainablesources.com/pipermail/gsbn/attachments/20121120/145aa7ef/attachment.htm>