effective R-value cavity insulation

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I am curious what the relationship is between cavity depth, rated insulation, and effective insulation in framed walls. I am referencing the ASHRAE 90.1 doc because it is really the only one I have on this subject. I have charted Table A9.2B and a logarithmic trendline appears to be a good fit for extrapolating. If anyone in academia, industry, or the societies has more information on this subject I would certainly be grateful to receive a good lead. Thank you.

Kevin Kyte, LEED (r) AP

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Joined: 2011-09-30
Reputation: 2


One reference for calculating U-Factors for wood-framed, metal-framed
and masonry walls is the 2009 ASHRAE Handbook - Fundamentals, Chapter
27. There is a section on "Two-dimensional U-factor calculation", which
describes the parallel-path, isothermal-planes, zone and modified zone
methods of calculating overall heat transfer rates through wall
assemblies. Earlier versions of Fundamentals (2005, 2001 etc.) will also
have some background information.


William Bishop, EIT, BEMP, LEED(r) AP

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Joined: 2011-09-30
Reputation: 0

Kevin et al:

Not sure if this is what you are looking for, but at any rate it is a very
good resource to share...

The folks at ORNL have developed a pretty cool 'calculator' which determines
complex wall R-values using the 'Modified Zone" method described in the 2009
ASHRAE Handbook of Fundamentals: Chapter 27. It's very easy to use, and
generates 'clear wall' R-Values for a user defined 'sandwich'. It also
provides a good visual as to how "clear wall" and vs. "whole wall" R-values
differ (for a particular 'hard coded WWR and user defined fabric

The calculator provides results for a limited set of various 'common'
configurations, and provides a good 'QA/QC" process if you choose to build
your own (spreadsheet based?) tool to expand it's capabilities

Here's the link:


There's also a 'tease' on this page
suggesting the folks at ORNL have plans "in the works" to assist analysts
with developing fabric descriptions:

New Features Include: Generation of Input Files for Whole Building Energy
Simulation Programs (in development)

Have fun!

Chris Balbach, PE, CEM, BEMP, CMVP

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Joined: 2011-09-30
Reputation: 1