Cob: Re: why light clay

[Kyle Towers]

    If the radiant barrier insulation you speak of is a moisture barrier as well, your liechtlehm and timbers may not last long.  Your winters may be short, but whenever it is colder outside than inside, moisture will migrate into the walls and be stopped by the exterior insulation, condense, and commence the unspeakable.
  ----- Original Message ----- 
  From: Vicki and David Wicker 
  To: coblist at deatech.com 
  Sent: Sunday, April 29, 2001 2:59 AM
  Subject: Cob: why light clay


  I will tell you our situation and explain why we have chosen a timber frame with light clay infill rather than a "regular" cob house. Opinions would be appreciated. We have dug out our place and are ready to pour footings but haven't begun actual construction yet.
  We live in central Arkansas where the weather gets very hot and humid during the summer. Although we do get some cold weather in the winter, you can heat your house fairly easily with good solar design, good insulation, and a quality wood or pellet stove. However, staying tolerably cool in summer is a whole nother ball game. I have spent hours looking for ideas on passive cooling but there just aren't the options for cooling as there are with heat. My concern with cob, adobe, and rammed earth is that, unlike in the Southwest where the temperatures drop off significantly at night, allowing the house to transfer its heat back into the environment, in our area night time temperatures remain in the high 70s and 80s for days, with high humidity to boot. Our fear was that our thermal mass would heat up with little or no opportunity to release that heat back into the environment and we would essentially be living inside a brick over for several weeks of the year.
  To try and minimize artificial cooling we have chose the following design. Our house will be set back into the hillside so that the back wall is entirely bermed with the front side walking out level. The front is southern exposure and will take advantage of passive solar. Berming in will give us the cooling effect of the earth, but I did not want to go the whole distance on an underground house. Also, since we are in the mountains, digging into the rock is expensive. Our cost to get deep enough into the hillside just for berming was $2000.
  Because of the berm, the back wall will be block and the side walls will be blocked to about 3 feet. It would be very expensive in terms of blocks or poured concrete to create a wide enough foundation to build the "pure" cob walls. In addition, we plan to build a living roof. We chose a flat roof (well, slightly sloped) to minimize surfaces that would be heated up by the sun. We chose the living roof to try to utilize the cooling effect of plant transpiration. We chose timber frame to give us the strength to hold up the living roof and because my husband is an experienced timber framer, which gives us confidence on structural integrity.
  As for the light clay infill, straw vs. chopped straw vs. sawdust, I assume people chop the straw so they don't have "hairy" walls. Why we are thinking saw dust over chopped straw is saving the extra labor of chopping the straw and saw mills are very prevalant in our area, so saw dust is readily available and cheap. We chose infill over making bricks with a cinva ram once again because of saving labor. We were fortunate to find a mortar mixer on its own trailer for about $900. We will mix the clay mix at the clay site, pull it to the wall site with our little tractor and pack it in the forms. Making bricks would require several more steps and moving the bricks several times.
  Once the walls are up we plan to wrap the outside in a radiant barrier insulation, once again to try to keep our thermal mass from heating up in the summer. We haven't decided yet on an exterior covering. The excavators dug up a lot of rock so we are considering rocking the outside. Oh, and we're planning on an earthen floor, once again to try and gain some cool in the summer, with radiant tubing for winter heat. We plan on a hahsa to run our radiant heat.
  We're forging ahead but still have our ears open to ideas, so if you see any major flaws in our plan, or have some suggtions for improvements we'd love to hear them.
  Vicki and David Wicker
-------------- next part --------------
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
<HTML><HEAD>
<META content="text/html; charset=windows-1252" http-equiv=Content-Type>
<META content="MSHTML 5.00.2314.1000" name=GENERATOR>
<STYLE></STYLE>
</HEAD>
<BODY bgColor=#ffffff>
<DIV><FONT face=Arial size=2>    If the radiant barrier 
insulation you speak of is a moisture barrier as well, your liechtlehm and 
timbers may not last long.  Your winters may be short, but whenever it is 
colder outside than inside, moisture will migrate into the walls and be stopped 
by the exterior insulation, condense, and commence the unspeakable.</FONT></DIV>
<BLOCKQUOTE 
style="BORDER-LEFT: #000000 2px solid; MARGIN-LEFT: 5px; MARGIN-RIGHT: 0px; PADDING-LEFT: 5px; PADDING-RIGHT: 0px">
  <DIV style="FONT: 10pt arial">----- Original Message ----- </DIV>
  <DIV 
  style="BACKGROUND: #e4e4e4; FONT: 10pt arial; font-color: black"><B>From:</B> 
  <A href="mailto:macmastr at cswnet.com" title=macmastr at cswnet.com>Vicki and David 
  Wicker</A> </DIV>
  <DIV style="FONT: 10pt arial"><B>To:</B> <A href="mailto:coblist at deatech.com" 
  title=coblist at deatech.com>coblist at deatech.com</A> </DIV>
  <DIV style="FONT: 10pt arial"><B>Sent:</B> Sunday, April 29, 2001 2:59 
AM</DIV>
  <DIV style="FONT: 10pt arial"><B>Subject:</B> Cob: why light clay</DIV>
  <DIV><BR></DIV>
  <DIV><FONT size=2>I will tell you our situation and explain why we have chosen 
  a timber frame with light clay infill rather than a "regular" cob house. 
  Opinions would be appreciated. We have dug out our place and are ready to pour 
  footings but haven't begun actual construction yet.</FONT></DIV>
  <DIV><FONT size=2>We live in central Arkansas where the weather gets very hot 
  and humid during the summer. Although we do get some cold 
  weather in the winter, you can heat your house fairly easily with good 
  solar design, good insulation, and a quality wood or pellet stove. However, 
  staying tolerably cool in summer is a whole nother ball game. I have spent 
  hours looking for ideas on passive cooling but there just aren't the options 
  for cooling as there are with heat. My concern with cob, adobe, and rammed 
  earth is that, unlike in the Southwest where the temperatures drop off 
  significantly at night, allowing the house to transfer its heat back into the 
  environment, in our area night time temperatures remain in the high 70s and 
  80s for days, with high humidity to boot. Our fear was that our thermal mass 
  would heat up with little or no opportunity to release that heat back into the 
  environment and we would essentially be living inside a brick over for several 
  weeks of the year.</FONT></DIV>
  <DIV><FONT size=2>To try and minimize artificial cooling we have chose the 
  following design. Our house will be set back into the hillside so that the 
  back wall is entirely bermed with the front side walking out 
  level. The front is southern exposure and will take advantage of passive 
  solar. Berming in will give us the cooling effect of the earth, but I did not 
  want to go the whole distance on an underground house. Also, since we are in 
  the mountains, digging into the rock is expensive. Our cost to get deep enough 
  into the hillside just for berming was $2000.</FONT></DIV>
  <DIV><FONT size=2>Because of the berm, the back wall will be block and the 
  side walls will be blocked to about 3 feet. It would be very expensive in 
  terms of blocks or poured concrete to create a wide enough foundation to build 
  the "pure" cob walls. In addition, we plan to build a living roof. We 
  chose a flat roof (well, slightly sloped) to minimize surfaces that would 
  be heated up by the sun. We chose the living roof to try to utilize 
  the cooling effect of plant transpiration. We chose timber frame to give us 
  the strength to hold up the living roof and because my husband is an 
  experienced timber framer, which gives us confidence on structural 
  integrity.</FONT></DIV>
  <DIV><FONT size=2>As for the light clay infill, straw vs. chopped straw 
  vs. sawdust, I assume people chop the straw so they don't have "hairy" 
  walls. Why we are thinking saw dust over chopped straw is saving the extra 
  labor of chopping the straw and saw mills are very prevalant in our area, 
  so saw dust is readily available and cheap. We chose infill over making bricks 
  with a cinva ram once again because of saving labor. We were fortunate to find 
  a mortar mixer on its own trailer for about $900. We will mix the clay mix at 
  the clay site, pull it to the wall site with our little tractor and pack 
  it in the forms. Making bricks would require several more steps and moving the 
  bricks several times.</FONT></DIV>
  <DIV><FONT size=2>Once the walls are up we plan to wrap the outside in a 
  radiant barrier insulation, once again to try to keep our thermal mass from 
  heating up in the summer. We haven't decided yet on an exterior covering. The 
  excavators dug up a lot of rock so we are considering rocking the outside. Oh, 
  and we're planning on an earthen floor, once again to try and gain some cool 
  in the summer, with radiant tubing for winter heat. We plan on a hahsa to run 
  our radiant heat.</FONT></DIV>
  <DIV><FONT size=2>We're forging ahead but still have our ears open to ideas, 
  so if you see any major flaws in our plan, or have some suggtions for 
  improvements we'd love to hear them.</FONT></DIV>
  <DIV><FONT size=2>Vicki and David Wicker</FONT></DIV></BLOCKQUOTE></BODY></HTML>