Cob: Oklahoma thoughts and concerns

[Shannon C. Dealy]

On Wed, 24 Jul 2002 bobodod at cox.net wrote:

[snip]
>     A friend brought up the concern that the extreme temperature and weather
> variations - strong winds and intense storms - we experience in Oklahoma
> would wreak havoc on a Cob building. He wondered if a change of 40 degrees
> Fahrenheit wouldn't crack the walls. Or just the very hot Summers and cold
> Winters might do the same. Any opinions on this? By the way, the climate
> here is slightly above average humidity, I think.

I don't think it is likely (I certainly haven't heard of any cases
attributed to this).  Cracking in cob buildings usually involves moisture,
either drying to fast or freezing while the building is being built.
Once the walls have dried for a while, they should never have sufficient
moisture again for this type of cracking to occur.  The only other way I
could see it happening is heat expansion and contraction, and with most
materials that I have worked with, that usually requires large, rapid
temperature changes in the material.  Cob with it's tremendous thermal
mass is very difficult to force through a rapid temperature change.


>     Another friend brought up another concern involving the heat here. In
> the Summers, the temperature often doesn't get below the high eighties,
> unlike the desert where the temp will drop several dozen degrees at night.
> He thought that with all of the thermal mass of a Cob building, the walls
> would not be able to shed the heat of the day at night. By the end of Spring
> and beginning of Summer, this could mean living in a sauna.

Depends on what you mean by often, if you mean the night time low for
many days or weeks at a time doesn't get below the high eighties, then
this could be a problem, if you just mean that some nights don't get below
that, then it is not so much of an issue as typical cob wall thicknesses
should take many days to undergo a significant temperature change
(with proper design for your climate you could probably stretch the number
of days significantly).

[snip]
> had buried a coil of pipe (not sure what kind), deep in the ground - at
> least six feet - several feet away from the house. He then ran pipe from
> that coil to pipe which he imbedded in the walls of the house he was
> building. My friend wasn't sure if the guy'd filled the pipe with water or
> what, but the idea was to let the Earth cool the liquid in the pipes
> overnight, then pump that liquid into the wall pipe in the morning,
> completing the cycle the next morning.
>     Has anyone heard of this? Any thoughts as to doing the pumping action
> with a modified bicycle if someone were wanting to be free of the daily
> electricity needs of the pump? Or would the physics of that be impossible
> (meaning a couple hundred gallons or whatever being pushed around by two
> scrawny human legs)? Would Cob dry and settle correctly with pipe buried in

There have been many variations on this approach tried over the years,
many quite successful,  As far as pumping with a bicycle, it shouldn't be
a problem, just depends on the design of your building and heat
transfer system, and how much time you feel like pushing the pedals, but I
don't think it would be an unreasonable about of pedaling time.  As far as
the cob handling the pipe in the walls, it depends on your pipe diameter
and your wall thickness, but there should be a reasonable compromise you
could reach between the two.

> it? I've heard that the Earth from about 6 feet and on down, stays at a
> constant temp of 72 degrees Fahrenheit. Can anyone confirm this? And if

Yes, sort of.  The earth's temperature is stable year round in most
locations once you get below a certain depth, but the depth and the
temperature it stabilizes at varies considerably depending on location.
I don't know for your area, but most areas I have looked into stabilize to
much colder temperatures, generally below 60 degrees, though they are
all cooler climates than yours.  As far as the depth goes, to some extent
it depends on what you mean by stable, a few feet will give you much more
stable temperatures than the outside air, but still might vary by 40
degrees over the course of a year, where at 20 feet in most areas it may
not vary by more than one a degree.  Somewhere in between you will
hopefully find a depth that is a reasonable trade-off between stability
and cost of digging.

Ultimately, this seems like a lot of work and expense for what you get.
Given your description, I would probably build a cob house with an earthen
floor, a straw bale wrapped exterior, well insulated roof, and limited
number of well insulated windows with wide overhangs to block any direct
sun in summer,  The heavy insulation of the walls, windows and roof will
keep the heat out in summer and the cold out in winter, the earthen floor
will provide a thermal link to the earth below, and if you are right about
the year round temperature being 72 degrees at six feet, it would not
surprize me if you didn't need any heating or cooling at all providing
you don't mind a wide but reasonable range of interior temperatures.  If
you are not right about that, then you will probably need some
supplemental heating system for winter (I doubt you would need any cooling
for summer with this approach and an earthen floor).

You should probably spend some time looking at books on solar home design
to get a better understanding of insulation, solar gain, etc., before
going much further with your thinking, so you can at least get a good
understanding of what some of the tradeoffs are.  Unfortunately, I don't
have any books on this subject that are less than 20 years old, so I can't
really recommend any since I think they are all out of print.  Any one
else out there have recommendations?

A few things to consider:

  1 - All things being equal, go with a passive system rather than an
      active one (like bicycle pumps).  Active systems are far more likely
      to break down.

  2 - Insulation is usually the cheapest way to deal with both extreme
      heat and extreme cold.  Sometimes (but not always) it costs more up
      front, but it is a one time cost that should last the life of the
      building, most other approaches require continual annual outlay of
      cash.

  3 - Maintaining a constant interior temperature year round is alot more
      expensive than letting mother nature partially have her way.  If you
      are willing to let the interior temperature drop to 60 degrees on
      the coldest days of the year and rise to 80 on the warmest, you
      can eliminate much if not all of the expense of heating and cooling
      (with proper building design).  This is not as uncomfortable as it
      sounds, your body evolved to be able to handle a wide range of
      temperatures, and (assuming you don't have any health problems) it
      will automatically adjust given time to make the adjustment.  Of
      course if you try to go from living at a temperature controlled 72
      degrees to some outside temperature extreme in one day you will have
      problems, the key is to set the upper and lower temperatures for
      your building and let the interior drift with outside temperatures
      between those ranges.  If it gets to cold, put on a sweater,
      otherwise if you just live with it for a while, pretty soon you
      won't notice it.  Starting with a narrower temperature range may
      help with the adjustment.  There is only one down side to this that
      I have found, when people who don't live like this are coming to
      visit, you need to remember to reset the temperature (assuming
      you have the means to do so) for the duration of their visit.

Shannon C. Dealy      |               DeaTech Research Inc.
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