3D Analysis of Integrated R-Value of Wall
Three years ago, there was a discussion between Martin Holliday and a subscriber named Ethan about the integrated R value of Nexcem/Durisol ICF walls with poured concrete inside. There was a lack of complete data or at least data that was easily available. I’m wondering, after three years,if Green Building Advisor is aware of more documentation publicly available that includes a three dimensional analysis of this particular product as urged by Martin Holliday. Has Oak Ridge National Laboratory, e.g. ever done an analysis since?
Martin Holliday in his discussion quoted the following from the Nexcem literature. “The Nexcem material has an R-value of 1.75 per inch. This means that all Wall Forms regardless of thickness have a basic R-value of R-8.2.” The math of this statement implies a total wall thickness of 4.7 inches. But there is not a total thickness of 4.7 inches of Nexcem material from one outer surface of the block (the inside of the wall) to the other outer surface 0f the block (the outside of the wall) all along the block from one end to the other end. I am assuming that the concrete poured into the air gap in the middle of the form does not contribute to the total R value of the filled block at all, and I am also ignoring for the moment the value of the insulation that is inserted into the inside of the form before the concrete is poured. So at least the two dimensional question that was asked but unavailable three years ago was: what would be the integrated or average R value across the entirety of a row of blocks that are filled with concrete, ignoring the additional insulation. The followup question is what is the integrated or average R value be across the entirety of a row that is both filled with concrete and which also has the insulation inserts. The next question would add the third dimension – integrating the R value from the bottom of the wall to the top of the wall to get an integrated or average R value for the entire wall. The answer for the entire wall would have to be something less than the maximum R value that the wall could have at any given point, just like the integrated value for a whole wall that has a conventional window in it is less than it is for any single point in the wall where there is no window.
This is the kind of information that the public really needs in order to fairly compare products. I hope that some analytical organization like Oak Ridge National Laboratory or a resource center like Green Building Advisor can follow up with an answer. I’d like to use the Nexcem product but I want to make an informed decision.
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