Fwd: Re: Cob: Insulating in cold climates

[Bob]

>Dear Julie et al,
>
>Understanding the physics of insulation might help you answer many of your 
>good questions.  Heat (cold) travels in three main ways.  You can feel 
>transmission when you put one end of a metal rod in the flame and the other 
>end begins to burn your fingers.  Every material will transmit heat or cold 
>at a different rate.  The metal rod will heat your fingers much faster then 
>a glass rod of the same shape, for example.
>Then there is convection  which uses a fluid, heat the water in your furnace 
>and because hot water is lighter then cold because it is less dense with the 
>molecules moving faster, it will rise though the pipes into your living 
>space.  
>Then there is radiation.  When you go out in the sun from the shade you feel 
>the radiated heat from the sun.  
>
>When the cold travels through your wall there is a kind of film insulation, 
>it is resisted as it moves from a solid material to an air space, for 
>example.  The more times it has to pass from solid to air and back in 
>traveling through one inch thickness of wall the better the insulation.  
>That is, of course, unless it can travel through other parts of the wall by 
>transmission, going around the air spaces through some solid material.
>Water greatly reduces the insulating qualities of anything.  The same 
>insulation damp will not stop the cold traveling through it anywhere near as 
>well as when it is dry.
>
>Lets look at the fleece.  In a blanket where it is dry and not compressed 
>you get excellent insulation because of all the air spaces.  Mixed with clay 
>in your cob wall there would be a minimum of air spaces.  I would say you 
>are wasting your good and valuable fleece.  Concrete is considered poor 
>insulation but there are chemicals that create many bubbles in the concrete 
>as it is setting up which make it light and better insulation.  
>
>Straw and sawdust and wood are better insulating materials because they have 
>pockets of air in their cells, or long open spaces with straw.  Compress 
>them as with Masonite and  you lose your insulating qualities, though it is 
>the same wood fiber.
>
>So in Canada you may want a heat barrier in the middle of  your cob wall 
>full of straw or sawdust or other material that has cell structure and will 
>not hold too much moisture.  I would like to see some of our cob friends 
>experiment by building a wall all the same thickness that had different 
>kinds of interiors.  One section solid cob,   one section 3" of sawdust 
>sandwiched in the middle, one section straw, not compressed, perhaps another 
>sections full of dry leaves.
>
>One of the problems with these organic materials is they are easily attacked 
>by rotting bacteria if they get damp or might even form passageways for 
>rodents.  An interesting technology is the use of Portland cement with these 
>woody materials.  The cement will bind shavings together into excellent wall 
>panels. They were extensively used in Scandinavia.  Its alkalinity will 
>inhibit rotting and make it so fire proof it will not burn.  The caution 
>here is the oil in the woody material.  If there is too much it will mix 
>with the cement and make soap, not a hard good binder.  Therefore it is 
>important to either get shavings or straw that have very little oil or wash 
>it off with detergent. Panels of this embedded in your cob wall or lining 
>the interior should considerably increase your insulation.  
>
>Another thing to consider is the due point.  Warm air holds more moisture 
>than cold air.  When the warm air seeps thought your wall it will reach a 
>point where it is so cold it drops some of the moisture in the wall.  This 
>can cause a problem if it can not get back out.
>
>Now lets take a jump into low cost no wood technology.  Lets make panels of 
>straw and Portland cement that can be used on the roof.  If the straw is not 
>flattened one could make a thick panel that is light, good insulation, fire 
>proof and rot proof.  It would not be water proof unless one could use the 
>system thatch roofs use to shed the water, steep slope with the straw all 
>running up and down the slope.  
>
>Then lets use the same straw to make the rafters and beams and trusses.  
>Here we will flatted the straw and run it longitudinally to the beam.  It 
>may be possible to create trusses just as strong as wooden ones without 
>cutting down one tree, and they will be more fireproof and less costly if 
>straw is readily available.  It would be important to remove all the chaff 
>which would probably just drink up and thus waste the cement.  This same 
>system would work well for all kinds of fibrous materials:  wheat, oats, 
>rice, hemp etc. a lot of which is now burned and wasted.. 
>
>If anyone has any information about this technique or tries it please get 
>back to me.
>
>Bob Luitweiler   <owl at steadi.org>
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>At 01:10 PM 6/18/00 , you wrote:
>>Hi.  I live in Canada too.  What's everyone's feelings about insulating
>>with sheep fleece? (presuming you can aquire it at a decent price).  How
>>would one go about incorporating sheep fleece insulation into a cobhouse
>>design? Would you need to go as far as an inner and outer wall?
>>
>>Julie
>>