bringing durable strawbale construction to wet climates for over 15 years
volume 1, issue 1
January 2012
 
designing natural buildings &
teaching hands-on workshops
Strawbale vs. Cob...
Not the Typical King Kong vs. Godzilla Story
 
by Sigi Koko
  
King Kong and Godzilla fought to the death.  One victor.  One “good guy”.  They didn’t walk off  into the sunset hand-in-hand at the end of the battle.
 
Not so for strawbale and cob.  There is no epic battle, no single "good guy".  For the question “Which is better to use for my natural building, strawbale or cob?” the answer is simple:  IT DEPENDS!  (of course...)  And often the highest performance comes when you use both materials together.  Strawbale and cob compliment each other extremely well, because each material possesses completely different properties.  So let's understand the benefits and limitations of each material so you will know how to maximize the attributes of both strawbale and cob.
 
STRAWBALES insulate.  Small air pockets trapped between the strands of straw slow down heat energy traveling from one side of the wall to the other.  The thickness of the strawbale walls ensures that there is A LOT of insulation between your cozy interior and the outside elements.   A good insulator acts like a down jacket that keeps IN your body heat instead of letting it disperse out into the cold winter air.  A well-insulated house will use less energy to heat in winter than a poorly insulated house, because the insulation keeps the heat inside longer.  If you use an air conditioner in summer, insulation will keep the heat outside, so again you need less energy to keep cool.
 
STRAWBALES work best...            ...as exterior walls anywhere you are trying to keep the inside temperature different from the exterior temperature.  The insulating strawbales keep the temperature exchange to a minimum, so the energy used to heat or cool the inside is minimize.
 
I RECOMMEND Build exterior walls with STRAWBALES if you live in a climate where a well-insulated home is more comfortable and cheaper to heat/cool.

 
 
COB provides thermal mass. The principal ingredients, clay and sand, are thermal mass materials that store heat energy.  Cob has limited insulating properties.  Instead, a thermal mass is like a storage battery for heat (or cool) energy.  This means cob is good at absorbing heat energy from the sun or a fire and storing that heat even once the heat source is gone.  When the air temperature around the cob is lower than the temperature of the cob itself, the thermal mass releases its battery storage of heat into the air.  In this way, cob can absorb a lot of heat energy and then release the heat over time, long after the heat source is gone.  Conversely, a shaded thermal mass with no heat input will stay cool in the summer and absorb heat energy out of the warmer air around it (thus having a net cooling effect).
 
COB works best...                                           ...as thermal mass built around a masonry heater or rocket stove (or near a wood burning stove), where the cob can absorb heat from the fire, and store the heat energy even after the fire is out.

...for trombe walls in passive solar design, with the cob thermal mass inside, where it is warmed by sun coming through South-facing glass.

...for any interior element when you are trying to keep the inside cool.  This can be the same thermal mass used to keep warm in winter as long as there is no heat source warming it when you want to stay cool.
 
I RECOMMEND Use COB where high thermal mass will store heat or cool energy…interior walls for passive solar strawbale homes or exterior walls in temperate climates or where daytime temperatures are warm all year round.

   
I usually use a combination of strawbale and cob.  The climate where I live and work requires several months of heat in the winter, and highly insulating strawbales exterior walls keep that heat inside.  This ensures that only a minimum amount of energy is needed to heat the spaces and the heat that is produced stays inside.  I then add cob to the interior, as my "temperature battery".  I surround a wood-burning heat source with 4-6" of cob or position a cob wall so that low winter sun shines on it from the South.  In winter, the cob absorbs heat and releases in slowly into the space, equalizing and warming interior temperatures.  In the summer, that same cob element is completely shaded and cool, so absorbs excess heat and humidity.
 
If you live in a mild climate where the temperature swings are day-to-night instead of seasonal, then a thermal mass exterior wall generally will help to average out those temperature swings...ie, cob.  However, note that building with cob exterior walls in a cold climate can result in a condensation point and moisture build-up inside your wall.  This can lead to mold problems and even freeze-thaw cycles inside your wall (which can cause the wall to break apart).
THANK YOU for subscribing to our Down to Earth email list!  In order to better serve our many subscribers, we've changed our list host.  We will still send you emails whenever new natural building workshops are scheduled.  In addition, you will receive this monthly newsletter, with upcoming events, recommended books, and in-depth articles covering various natural building topics.  You can manage your subscriber preferences online.  And as always, your feedback is highly valued!
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in this issue...
• Feature Article:
"Strawbale vs. Cob...Not the Typical King Kong vs. Godzilla Story"

What's Happening
   upcoming events

Low Hanging Fruit
   simple eco-living tips
 
Recommended Reads
   natural building books
what's happening
Part Two of the Cob Oven video is up and ready!
Part 3 coming soon…
 
Stay tuned for Spring Workshops.   We are currently working on details for a natural paint workshop in April and an earthen floor workshop in May or June.  Hope to see you there!
this is where we will be painting inside with colorful, non-toxic homemade paints & installing the final layer of adobe floor
low hanging fruit
small habits that make a  big difference...
 
Choose regular soaps instead of antibacterial soaps...unless your doctor specifically recommends otherwise
 
The fact is that washing your hands with ANY regular soap removes bacteria!  The antibacterial agent is completely unnecessary.  Meanwhile, those antibiotics get washed into our waterways and damage our ecosystems.  The overuse of antibiotics can actually lower your immune system over time and is linked to the evolution of bacterial “superbugs” that are resistant to antibiotics.  To read more click here(There’s a recipe at the end for a natural, all-purpose disinfectant you can make at home.)
recommended reads
 Building Green by Clark Snell & Tim Callahan
 
great “how to” guide covering a wide variety of natural building techniques & includes instructive step-by-step photos
 
 
click the cover above for more info or to purchase
 
Feel free to EMAIL ME if this article inspires any suggestions or questions.  CLICK HERE if you prefer to read this article online.  Or CLICK HERE for additional tips on how to build with strawbale in a wet climate.  
 
Thanks for reading!
 
Down to Earth Design
12 Forest Avenue   |  Ambler PA  19002
202-302-3055 DC   |  215-540-2694 PA

 
copyright ©2012 Sigi Koko & Down to Earth Design