R Value Myth, an interesting read

[AaronB.]

http://www.monolithic.com/stories/foam-chapter-04




***Admin - sorry AaronB. google has a problem with duplicated content so I just added a link to the article.

[concretemasonry]

Aaron -

You are absolutely correct about the misleading and archaic concept of an "R -value" being the measure of the insulation value of a system, the performance of a structure in the real world.

It is just a simplistic marketing supported test created to supposedly prove the lab value of a small segment of the material (not wall system) under ideal short-term lab conditions.

The most irresponsible example is the fiberglass data information that says it will give an R19 value in a wall. In the "semi-real world" it will give about R17 in a wood wall and as low as an R10 in a steel stud wall. The technical term for this difference is "thermal short circuiting". On top of this, is that the insulation factors are based on short term results in a cheap and fast hot box system and not the long term dynamic cycles that reduce the claims significantly.

This is neglecting the air infiltration that come with some products, but not with continuous barriers.

On top of that, there are also mass credits for some types of of construction that give some partial limited credit for mass based on annual climates.

Dick

[AaronB.]

Tell me more about these mass credits.

Rich, its all good, but how does google treat such duplicated content? The reason I ask is this article is duplicated all over the web.

[concretemasonry]

Last I was aware of, the mass factors are included in the ASHRAE standards. They depend on the mass of the wall and the location (degree days). The factor was multiplier used to increase the simplistic R-value to reflect the benefits of mass. They are not perfect, but they are a step in the right direction toward the real world thermal performance of a wall system.

I don't think they differentiate the difference in the location of the insulation (if any), but everyone realizes that exterior insulation that keeps the wall mass inside of any insulation is far superior. - Comfort and economics. It has been a while since I last applied them

Dick

[Rich]

I saw that when I searched for it AaronB - very duplicated. Here's another interesting read on how Google perceives it
http://www.google.com/support/webmasters/bin/answer.py?hl=en&answer=66359