Snap Shot of Thermal Mass

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Deep Summer, Deep South Graph of Data Gathered During Study


The Graph above was part of a Clemson University Thermal Study at the HFA Field Test in Columbus, Georgia.  Each spike represents one day.  The black line represents the exterior wall temperature which reaches 110 degrees Fahrenheit during this period.  The red line hovers a few degrees around 70 despite the outside wall temperature some 12 inches away.  This is the power of thermal mass at a glance.

The predominantly accepted climate for effective thermal mass has been limited to Southwestern United States type environs where extremely wide diurnal swings occur.  But the data here shows clearly that when one of the most ancient forms of building is coupled with new technologies such as a foamed rafter envelope, a surprisingly energy efficient combination occurs beyond the Southwest boundary.


  1. Wondering if there is a way to use this data to predict the performance in a New England winter? I live in VT and love structural brick. Our quaint villages have many old & loved brick buildings. Could structural brick construction be brought back in New England?

    1. Author

      Chad, I believe it can. There’s still a lot to be learned on the subject and Clemson’s thermal mass study is ongoing. We know computer energy modeling is inadequate in terms of realizing the full potential of mass wall masonry. I think most importantly as we enter into new ways of consciously determining new built environments, we have to think about balance. There are many issues and concerns at hand and there is no silver bullet that addresses them all to the utmost at once. But a good starting point seems to be this, “First, we must make things that last.” I came across this quote in a broom advert that was making its wares from industrial byproducts. It’s top to bottom application speaks volumes to me. But if we don’t start here, too much is lost right out of the gate. Will we reach zero energy with a mass wall in New England? Doubtful. But who’s to say we won’t discover something better when the final tally is counted.

    1. Author

      Eric, A foamed rafter envelope (also referred to as a foamed rafter cavity) basically involves the spraying of either an open cell ore closed cell Icynene foam against the underside of the roof decking between the stick framed rafters. In Atlanta where an R-30 is required by code in roofs or ceilings with standard batt or blown in insulation, an R-19 is accepted in foam because it performs so well in terms of infiltration and barrier protection. This amounts to 5″ of open cell and about half that in closed cell. Apologies for the delay.

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