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Myth: “ICF’s are an R-value of 50”
Not exactly. An R-value is the measure of resistance (R) of heat flow. Heat flow can be resisted by insulating materials such as plastic foams or mineral fibers, or can be slowed by massive dense materials such as thick masonry or concrete. The larger the R-value, the greater the resistance and the better the insulating value.
All building materials transfer heat to some degree. Heat transfer can be measured by any of the following: (1) conductivity (k); (2) conductance (c); (3) transmittance (U); or (4) resistance (R).
The ability of dense materials to retard heat flow depends on their ability to store heat and is measured by specific heat and heat capacity. (BTU per lb. Per degree F. ; Density lb. Per cu.ft.; Heat Capacity BTU per cu.ft. per degree F)
When it comes to stating R-values in residential construction, the insulation values applied to a wall or ceiling typically refer to the R-value of the insulation material that is installed, not of the wall or ceiling assembly. (For example, a 2x4 stud wall is insulated with an R-11 batt type insulation, the builder states that the wall is an R-11.) This is not totally accurate since approximately 20% of the wall is not insulated at all. The wood framing and sheathing do have an R-value, but for the sake of making insulation claims, they add very little. The real R-value, or PERFORMANCE R-value ends up at about an R-9. Add to this, the fact that the wall is full of penetrations, such as electrical outlets etc. and the fact that the wall itself is basically hollow in nature. This added thought leads to another discussion on air leakage through the wall.
With ICF, the TRUE insulation value of the wall is that of the Expanded Polystyrene (EPS). The insulation value of the EPS is determined by the density and thickness of the material. Some ICF systems have EPS that is of differing thickness (waffle and post and beam systems) that typically average the thickness of the foam. This is in our opinion not an accurate measurement since a bucket with a hole in the bottom doesn’t carry as much water as a solid bucket with a hole at the top. Most ICF’s utilize EPS foam that is in the range of 1.5 lb/cuft to 2.2 lb/cuft. The insulation values differ only slightly in that range.
The claim that ICF walls are an R-50 started a few years ago after the Insulating Concrete Form Association (ICFA) and several members commissioned CTL Laboratories in Chicago to perform some R-value testing and analysis. The summary of the report basically said that depending on the climate zone, the PERFORMANCE R-values are as high as an R-52 when compared to typical wood frame and batt construction. In order to make the comparison correct, one must insure that the comparison is being done vs. the alternative to ICF on the particular project. On average, the performance R-value is much less than the claimed R-50. Research by the consumer must be done to clarify the comparison for the actual project. In short, ICF will PERFORM at an R-50, but that statement is not accurate as far as an insulation value goes.
For more information on Insulation values, try these websites for research:
Iris Communications: www.oikos.com
Energy Star Program: www.epa.gov/energystar
Concrete Homes: www.concretehomes.com
Oak Ridge National Labs: www.ornl.gov
Energy and Environmental Building Association: http://www.eeba.org/