Equal R-Values Do Not Mean Equal Performance.
Green building professionals of all stripes need to remember that two walls with equal R-values may not have the same thermal performance. Every time this fact is ignored, opportunities to maximize energy efficiency and sustainability are lost.
Here's an example. I have an ICF (Insulated Concrete Form) wall with an R-22, and an NRG Insulated Concrete Block wall with an R-22. Architects, engineers, and codes treat the walls the same. They are not.The ICF wall has isolated thermal mass, and the NRG wall has insulated thermal mass.
The ICF wall has high thermal mass, but the interior wall insulation negates the effects of the thermal mass. The NRG wall also has high thermal mass, and its thermal mass is exposed to the building's interior. Its high heat capacity and long thermal lag time act to moderate the indoor air temperature, and produce more energy savings than the ICF wall.
A more accurate measure of a wall's thermal performance is the thermal time constant, which takes into account the relative placement of the insulation. An NRG wall has a much higher Thermal Time Constant than an ICF wall. In talking to architects and engineers, it is clear that the majority are unaware of the benefits of insulated thermal mass verses isolated thermal mass, and perhaps this is why they keep putting the insulation in the wrong place.
Does anybody have a suggestion as to how to incorporate the benefits of insulated thermal mass into the green building codes?