Re: [papercreters] Re: Insulation Value

I agree with most of what is said by ElfN here, although I wish I knew who MD is.   R-28 seems more than enough.   I've got that in my 8" walls and last year read an article saying that 6" walls with fiberglass insulation was more than enough and after that it is wasted money.   The law of diminishing returns applies here as in so many areas.   I wasn't really asking where that point is, and I don't need to know, yet it is an interesting question.   With all the studies out surely someone can plotted that curve.   If only I had saved that article I read last year.

 

Neal 

 

-------------- Original message --------------
From: "ElfNori" <elf@elfnori.com>

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

 

----- Original Message -----

From: slurryguy

.

I do not agree with your presumptions about insulation thickness.

> Urethane foam over 4" thick gives very little additional insulation
over
> what is achieved in 4".
>
> EPS over 6" shows little benefit.
>

While these rules of thumb may have been accurate at one time, for
typical stud frame construction, in a typical temperate climate in
the U.S., they were intended to create maximum profits for commercial
builders and suppliers. Please quote your source for these numbers.
Who said it?

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