I have always wondered why a sandwich of polystyrene and concrete is considered green, and have taken significant abuse for my position on insulated concrete forms (ICF). Now an interim report from the impressive-sounding MIT Concrete Sustainability Hub attempts to "deliver a new level of clarity" to the issue, and "to demonstrate the potential energy savings due to the benefits of thermal mass, effective insulation, and reduced air infiltration" with an elaborate comparison of apples and oranges.
The study, (PDF Here) funded by the absolutely impartial and disinterested Portland Cement Association and Redi-Mix Concrete Research Foundation, finds that yes indeed, ICF homes "deliver energy savings in heating, cooling, and ventilation." But compared to what?
For residential buildings, insulated concrete form (ICF) construction can offer operational energy savings of 20% or more compared to code compliant wood-framed buildings in a cold climate such as Chicago.
So they are comparing a premium product like an ICF that has an insulating value of R-40 or more to a conventional new code-compliant building built to ASHRAE 90.2-2007, "the minimum energy-efficiency requirements for the design and construction of new residential dwelling units", and quelle surprise, it uses less energy. That delivers lots of clarity. But what if they compared it to another premium product, like a structural insulated panel, or a passivhaus, or any other R-40 wall?
Blower-door testing has demonstrated that ICF homes achieve tight construction with minimal air infiltration, which improves the energy performance of residential construction.
Again, compared to what? A code compliant house with a 6 mil poly vapour barrier or another premium system where attention is paid to air infiltration?
Then there is my bête noire, the embodied energy in the concrete and the CO2 released in its production, and the fossil fuels and flame retardants used to make the polystyrene forms. According to the comprehensive life cycle analysis:
Because use-phase emissions are much larger than pre-use and end-of-life emissions, this same percentage is a reasonable estimate of life-time savings in carbon emissions associated with the use of ICFs. The energy savings can compensate for the initial carbon emissions of the concrete within a few years of operation. More than 90% of the life cycle carbon emissions are due to the operation phase, with construction and end-of-life disposal accounting for less than 10% of the total emissions.
But they are talking about a 75 year life span. That is a lot of emissions, and 10% of that is a very big number, which they decline to state in the interim report. And are they going to compare it to another, say wood framed house insulated to R-40 with cellulose or icynene?
The investigators have only released an interim report without data, but on the face of it, their conclusions are completely obvious and equally meaningless.
In their 2004 study Insulating Concrete Forms Construction Cost Analysis (PDF here) The Portland Cement Association found that ICF walls cost double what a conventional 2x6 insulated wall cost. There are half a dozen greener ways to achieve the same results with that kind of money. Doing a study comparing ICFs to code-compliant walls isn't even comparing apples to oranges, it is more like comparing apples to bicycles, a completely pointless and tautological exercise.
More at Builder Magazine, found on Jetson Green
More on insulated concrete forms:
Insulated Concrete Forms: Another Opinion
Polystyrene Insulation Doesn't Belong in Green Building
Another Reason to Laugh When They Say that Concrete is Green
How Should We Really Measure Green Building?
GreenBuild: Durisol, the Green Insulated Concrete Form