For this installment of manic monday I want to talk about an interesting product that, according to the last lunch presentation I sat through, has been around for far longer than it’s been popular – ICF (insulated concrete forms).
ICFs are really nothing more than a modern lightweight concrete formwork on crack. A typical ICF wall is 6-9 inches of reinforced concrete mass sandwiched between (2) 3″ foam panels. The foam is typically either EPS (expanded polystyrene) or XPS (extruded polystyrene). Both offer excellent insulation values (about R-3 or R-4 per inch, or about R-20 for a typical wall).
These R values only take into account the foam insulation however. To get a true measure of the total R-value of a wall you have to look at all of the components. The one overlooked being the concrete itself. A 6 inch thick concrete mass doesn’t carry a lot of R-value. But what it does do is create thermal mass. Thermal mass is a material’s ability to store heat. In this case, the concrete is able to store the heat energy that isn’t insulated by the foam without allowing it to pass into the conditioned space beyond. Many say that a typical 6″ ICF wall will yield between R-30 and R-40 in reality. I don’t know about you, but that’s pretty damn good.
Another groovy benefit to ICF is construction time. The forms themselves are modular and extremely lightweight. This makes for very rapid assembly. A crew of 4 or 5 can assemble an entire home ready to be poured in a matter of hours rather than days or weeks with traditional concrete form work. Not to mention, once the forms are in place, your insulation is already in place as well, so we basically skip a step in the whole process.
There are some drawbacks, however. One of the most unfortunate, in my mind, is that you are essentially required to finish out a basement space, since you can’t leave the foam exposed. Now, there are systems that let you form the concrete on the interior or exterior face only, leaving one side exposed, but then you’re cutting your R value in half, which ain’t so nice in my opinion, but in the case of a basement will most likely be a non-issue in terms of insulation.
So the next time you’re contemplating that new home or even addition, below grade or above grade, think about ICF construction. It’s modular, easily formed in place (minus the concrete pouring obviously) and quite literally solid as rock. There are all sorts of custom shapes that can be made due to the nature of the form material, so it’s ideal even for the most modern and out there architectural styles.