by Ian Giesler
Insulation. Every little bit helps, right?
In many parts of the US, the typical above-grade ICF project starts with a slab on grade. When ICF is set on top of a slab, the insulation only begins at the finished floor level. What about the slab edge insulation? A great deal of heat or cold energy is transferred via the concrete slab. (1)
When constructing the ICF wall, there is a tendency to cut the top course of ICF to meet a plate height and start the ICF wall with a full-height form. This scenario typically wastes the portion of the ICF that is too small to use along the top of the wall.
If the first course is ripped instead of the top course, the exact height must be determined in advance and could lead to an error if the layout person’s math is incorrect, but the trade-off is that perhaps half of the trimmed off piece of ICF could extend below finished slab level to provide for some slab edge insulation. Of course, the code minimum of 6” clear to soil would still be a requirement, but at least the attempt to provide slab edge insulation is there.
This photograph depicts a form that is cut symmetrically so that there is no waste of form, and it just so happens that the wall height will be exactly as required. Yes, this option as shown uses more ICF in the long run, but it is providing the required insulation that the architect specified.
This concept is not always feasible, but it is an attempt to bring awareness to the issue of slab edge insulation and the energy loss that is attributed to it. It’s about making sure the customer doesn’t complain about cold or hot floors due to the transfer issue.
On this project, the structure is to have a stucco cladding, which makes this easy to do. If a brickledge is required, there are several options to providing an insulation break to the slab, but the application shown could still be used with the brickledge set 4-6” below the finished floor level. (2)
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