Is injecting foam into the cores of CBS walls worthwhile for Florida homes?
Since the foam only fills in the block cavities there is still very significant thermal bridging around the insulation via the concrete block, making only a very low incremental cost for the insulation cost-effective from an energy standpoint. A rigid insulation that covers the entire wall surface will greatly reduce the bridging problem. In general though, walls are typically a relatively low part of a Florida home’s total cooling load (~ 7 – 10%). Let’s look at an example. The annual energy use savings (cooling and heating) for a 2100 sq. ft. example central Florida house (efficiency just above the 2001 Florida Code minimum), going from R-0 CBS to R-4 CBS (with e.g. a rigid sheet insulation) was $74, and going from R-4 to R-10 was $45. Each house will be different of course, but this example at least gives some idea of the relative impact, and how the benefit decreases as we get into higher R-values.
