[Strawbale] At what point (R value) do we reach 'enough' insulation?

[Coralie & Andre de Bouter]

  Dear Henryk,

  I did not experiment, I have my informtion from several presentations I've seen in the US.
  What I understood is:
  When you add 5cm of insulation to a non insulated building it will make a big difference.
  However, when you add 5 cm to a building that allready has 100cm of insulation it will hardly make a difference. 
  That is how the diagonal (increased insulation) becomes a curve. 

  This argument was expressed in relation to the discussion about the R value of SB. Some tests show better results than other, but all agree that the insulation is 'Good enough!' since they surpassed the angle in the above mentioned curve.  I could contact 'them' in America, but they use an other R value than we do in Europe. They state about R 40 for SB where in Europe it seems to be R 6. I don't know how to convert from the American R to the European R.

  I agree that the decision on what is good enough depends on "prices of buildig materials and labour and on the cost of energy for heating  (cooling) you would find acceptable" However, in one building system the optimum could be much lower than in an other building system. 

  So, if we take the price of the insulation and heating out of the calculation (since some insulation materials are extreemly cheap like straw or sheep wool, and energy prices might sky rocket some day), at what point is it 'enough'? I do realize that defining 'enough' ('reasonable optimum') will probably be difficult.

  I want to know this because it can give a scale to judge the effectiveness of a certain solution relative to the 'reasonable optimum'.
  Rather than giving just an R value (which I feel is only a number as long as we don't have a frame to place it in)

  I hope this clarifies my question,

  Greetings,
  Andre


  Hi Andre and Coralie,
  Could you explain how did you get the curve of thermal resistance R vs thickness of straw layer x? Can you send me the data obtained in your experiment?
  You suggest that R value is not proportional to x. Possible reasons : 1)not uniform properties of straw, ( for example higher moisture content in the exterior part of bale), 2) error in experimental procedure. That why I ask you for additional data.
  I guess that the answer at the question At what point (R value) do we reach 'enough' insulation?  depends on Amities Henryk Czachor

  -----Original Message-----
  From: Coralie & Andre de Bouter <m.ep at laposte...>
  To: ESBN <strawbale at amper....muni.cz>
  Date: Monday, June 24, 2002 10:27 AM
  Subject: [Strawbale] At what point (R value) do we reach 'enough' insulation?


    a question : 

    When we draw the relation between insulation in cm and the thermal resistance obtained we obtain a curve.

    For example:
    0 cm insulation > 0 thermal resistance
    5 cm insulation > x thermal resistance 
    10cm insulation > 3x thermal resistance 

    curve starts to slow down...

    50 cm insulation > 30x thermal resistance 
    100 cm insulation > 40x thermal resistance 

    So at some point it is as good as useless to increase the insulation because it hardly adds up to increased performance.

    ***The the million dollar question is: At what point (R value) do we reach 'enough' insulation?*** 
    I guess this is relative to the climate, is there any objective way of calculating this? 

    I ask this because other ecological/natural building systems do not offer R6 (R=m².C/W), but I would like to form an idea on at what point we can say it is well enough insulated. rather that bluntly stating that SB has the best R value. (a bit like saying a Ferrari can do 300km an hour, when 100 km an hour is enough)

    I know that some other building systems fonction in a different way (storing the heat or cold in thick high mass walls for instance) but I'm only looking to the insulation approach here.

    Greetings,
    André
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