It isn't so simple as one dependent variable and one independent
variable. There are multiple independent and multiple dependent
variables. In in the most simplified form there are multiple curves
and it is important to be looking at the correct curve for each
particular situation.
The price of crude oil has doubled in the past few years. Other
fuels, (natual gas, lp) have had significant increases as well, but
perhaps not doubling. Has this been factored in to MD's analysis?
My point is that the break point varies depending upon a variety of
circumstances. Climate is critical. Janaoah is in Alaska. The
break point there is going to be drastically different than the break
point in Italy Texas.
I'm certainly no expert in MD's construction techniques. Is there a
engineering factor involved where creating an insulation envelope
greater than 4" increses the complexity of their techniques? The
very little I understand about what they are doing leads me to
suspect this is the case, but I'm not sure.
In stick framing, the thickness of a wall stud is a major factor. Go
thicker than that and costs skyrocket. While this doesn't apply to
what MD is doing, it does illustrate how a construction technique can
impact the cost structure.
Simple rules of thumb that say x-number inches of insulation are
optimal are narrow sighted. I'm pulling together research off the
web to make my point. I'll do my best to explain the math. I think
I can make this easy to understand.
I'll be posting later about this and provide documentation, maybe
tomorrow, more likely this weekend.
--- In papercreters@yahoogroups.com, "ElfNori" <elf@...> wrote:
>
> I know MD's philosophy is that urethane foam over 4" isn't value
added. The improvement in insulative value drops off with increased
thickness to the point the cost of the insulation isn't returned by
the improvement in performance. Any insulation (continuous, not
broken by studs) has a point at which adding more thickness adds
expense without value or savings return.
>
> To put it another way, bearing in mind NONE of this answers Neal's
question, insulative value thickness to performance is a curve, not a
straight line. On that curve is a spot where you get the most
insulative effect/performance for the $ expended. Neal is asking
what the thickness is at that point.
>
> Neal, I don't know that anyone has that answer for you, though
there are a couple on the list who might be willing to postulate
based on personal experience/inference.
>
> I think there are a number of reasons we don't have a set figure
for this. One is the relative newness of the building material.
Another has to do with the inherent properties of papercrete. It is
both an insulation AND a thermal mass, so conventional methods of
measuring insulative value cannot truly reflect the performance of
this product. There is also a variance in performance based on
recipe and application. Like urethane foam has different densities
depending on the mix/ingredients, papercrete has different
performance depending on ingredients/application. Blocks that
constructed using compression have better thermal performance than
uncompressed blocks. Sand in the mix increases thermal mass and
decreases insulative value.
>
> There has to be a sweet spot on the thickness curve, and I think
finding it for the most popular recipes is key.
>
> ElfN
>
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