Message Board Thread - "R-value calcs"

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R-value calcs JohnW 12/5/2010
As a recent level 1 student, I am wondering if R-value can be calculated by analyzing an exterior image opposed to an interior one?
I read R Maddings abstract and looked at his Excel calculator but it only works with an interior image.
Can someone please explain why and/or lead me to a calculation that will work with an exterior image. I do have an interior temp value.
Re:R-value calcs Gary Orlove 12/6/2010
Its basics physics. The temperature differentials on the wall exterior between poorly and well insulated sections are MUCH SMALLER than the temperature differentials on the inside, this leads to a MUCH GREATER ERROR potential.

The climatic conditions on the inside can also be controlled, (steady temperature, no wind, etc.) but exterior temperatures, wind velocity, and solar gain, cloud cover etc. cannot be controlled.

All of this means that doing an R value calculation is much more accurate, and repeatable, from the interior of the building.

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