Cob/Cordwood Masonry Hybrid

[Renewables at aol.com]

My experience is not with the thick cob walls, so I've had to go elsewhere for
comparison. The closet we can come in the area is with concrete cow barns and
sheds. The walls are not as thick as cob walls, but the mass has more or less
similar characteristics. I have been in several traditional adobe building and
interviewed the owners to gain a comparison experience.

I choose not to derate the performance of cob, so newcomers should not look
for that message in my posts. I have followed this list for some time, but as
of yet hadn't had the opportunity for more than a couple wheel barrows of it
at a regional workshop.

My original intent was to add the cob building technology to our future
project to reduce the dependence on cement products or materials. Cordwood
masonry fits very nicely with the over used "warm in the winter, cool in the
summer" phrase. If cob can be added to reduce the cement contents, so much the
better in my opinion.

Our original experiment was to come from a single story round 38.8 foot
diameter (~1,000 SQ. ft) earth roofed building. Some designs called for rear
earth berming on the North side. The phase used concrete blocks with surface
bonded concrete. This is still a possibility, but I'd like to examine other
options first to try and eliminate much concrete as possible.

The earth roof has an eight inch thick sod over gravel, #2 stone, tu-tuff, 2"
insulation, and 1:12 sloping plywood roof (sloping from center). This alone
does help keep the building much cooler. It also has a history of lasting much
longer than most other roofs if installed properly.

Cordwood is very strong and is load bearing with no problem. The earth roof
support comes from a center masonry heater, center girders amid the radius,
and the cordwood wall.

The trick would be to get the inner and outer cob wall thick enough to
duplicate the traditional cordwood strength (with little or no cement
content). At this point no expert has calculated this. Although the center 1/3
of the wall will be insulation in the form of chopped straw, softwood sawdust,
shredded newspaper, or Vermiculite, all held together via a 16"+ cordwood
logend, it surely will not be as much as a layer of straw bale insulation
placed on an external cob wall. Our local straw is pretty much oat straw, no
local wheat straw is available. I'd like to stay with natural locally
available materials as much as possible. Although the cordwood wall center
space is 1/3 insulation, the cordwood logend (penetrating 1/2 inch through the
inner and outer wall) is of a lighter wood design and helps to enhance the
walls overall insulation value.

Again, this is more of an exercise to determine if the project is feasible
than one which has been proven to be so.

The climate in the upper Midwest is interesting. The average 76 degrees you
speak of in Illinois is not a typical temperature, but you stated is
indicative of the average of the days highs and lows averaged over a 24 hour
period. Typical June 15th - September 15th daytime temps range from 82 deg F
to 95 deg F. Night time temps range from 55 deg F (good sleeping) to 75 deg F.
Exceptions are cold fronts that bring rare 70 degree air for a day or two at a
time.

Our humidity usually raises at the end of the summer day. It is usually 60 -
80% in the early morning, but raises to 90-95% by late afternoon-evening.
Whole house fans work well after 11PM local time. Exceptions are the rare cool
fronts that also bring drier air temporarily. Most of our fronts actually
increase humidity.

Earth sheltered homes work real well in this area. To prevent dewpoint
condensation, rigid insulation must be applied to the underfloor (with vapor
barrier), rear walls, and footings. Unfortunately, this design usually uses
large amounts of concrete and is something we're seeking to eliminate as much
as possible.

I'm looking forward to reading/learning/practicing more about cob and its
related technologies over the next few years. Our schedule calls for building
our home in about five years after our son graduates from high school. We plan
on a slightly downsized home, but also want to practice with several smaller,
but increasing larger projects to gain experience first. Efforts to find other
local like minded individuals has not panned out. We're hoping to form a loose
bond community of several other like minded folks nearby. There are only a
couple counties NW of here that allow for less than forty acre subdividing to
prevent urban sprawling from the city. Forty acres locally will currently cost
us more than what our future home will. If we find forty acres NW of here in
SW WI or NW IL, we can subdivide it to ten (or even five) acres apiece and
have room for each person's definition of self reliant living. Unfortunately,
that land is 60 - 90 miles away, affording only weekend and holiday trips to
the building site. Therefore we are a little over halfway on our get out of
debt project, allowing us to build debt free in the future and live a
simplified lifestyle to reduce or eliminate regular commuting after building.
PV, wind generator, passive solar heat, organic garden, three season attached
greenhouse ... low impact lifestyle. What could be more inspiring to
demonstrate simple living to others? That will hopefully allow us to show
others how to develop a similar plan afterwards.

Until then, we will (read more about) cob on!

Dave

In a message dated 11/1/98 5:10:10 PM Central Standard Time,
cobcrew at sprynet.com writes:

 Dave says:
 [snip]
 >>Also, the sustained 90+ degree F
 >> temperatures with the high 90+ percentage humidity of late August would
 >> eventually raise the internal home temperatures to the uncomfortable
 stage.
 >> You would end up having a building with its weak points in March and
 >> September. The cold would be catching up with it in March and the warmth
 in
 >> late August (at least in N. Illinois).  >>
 >
 >Really good analysis of Cobs weakness in such extreme weathers.
 
 Yes, I'd want some straw minibales (or other extra "outsulation") on the
 outside of a hybrid cob/straw house in Illinois.  Summer should be no
 problem, as average temps are 76 degrees F max for Illinois.
 >
 OK, now this is what I have direct experience with here in Texas.  Some nice
 extreme hot weather.
 1)  You will find humidity varies during the day.  In the summer here, it
 starts at around 90-100% in the AM and often drops to 30-40% in PM.  The
 clay in the cob has a proven ability to buffer humidity, which will make
 your home feel cooler.
 2)  Get some stats on the average temperature during a 24 hour period.  In
 Austin, we had the hottest June on record, with 95 degrees or more for a
 high much of the time and 108 one day (we cobbed that day).  The average
 temp. for the month was 86 degrees.
 This is because the high was only reached for a few hours during the day.
 The thermal mass will tend towards that average temp.
 
 There are many design factors which will make a house more livable.
 (Ceiling fans, good window placement and ventilation, large South and West
 eaves, trees, a living wall, ventilation at the top of a peaked roof, good
 window quality and seals, etc.)
 
 All kinds of stick-framers visited our place this summer and commented on
 how cool it felt in the afternoon without even any doors or windows.
 
 Mike Carter
 cobcrew at sprynet.com
 http://home.sprynet.com/sprynet/cobcrew
 Austin, TX    USA
  >>