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

[henryk czachor]

Dear Andre,

    If you add 5 to 5 you have 10, and 5+100=105. In both cases the increase is the same, but their relative changes are 100% and 5%  respectively. So we have to clarify about what changes we are speaking about. Any way for homogenous materials R is simply proportional to thickness x ie R=r*x
    It would be very interesting  for me to know the source US data. In USA they still frequently use Btu as the energy unit= 1058J, 1ft= 0,305m, 1F=0,55C,1pound=0,405kg ,Probably the conversion between them  can be done as follow  R US  [hr-sqft-F/Btu]/5,74 = R  SI [s-m2-K/J]. The European unit is roughly speaking 6 time bigger.
    Rene's remarks are great-one have to take into account much more data then you proposed to calculate the total heating power of your house. Once again about "enough". If the price of energy is zero you can use very poor insulation and it will be optimal one (from economic point of view). When "energy prices might sky rocket some day" such house would desequilibrate  your budget (or rather mine). I observe such phenomenon in Poland. Since 10 years thousands and  thousands of old big blocks (immeuble) and small houses are additionally insulated because the energy costs much more now. 
Perheaps when you are speaking "enough insulation" you are thinking about "friendly house" - friendly for your family,pocket and enviroment.
Greetings Henryk
-----Original Message-----
From: Coralie & Andre de Bouter <m.ep at laposte...>
To: strawbale at amper....muni.cz <strawbale at amper....muni.cz>
Date: Tuesday, June 25, 2002 2:23 PM
Subject: Re: [Strawbale] At what point (R value) do we reach 'enough' insulation?


        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
        

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