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# How do you model slab-on-grade insulation?

My colleagues and I are having difficulty understanding how to manipulate IESVE to model an existing slab with 24" of slab/foundation insulation in both horizontal and vertical planes. The property set seems to limit to either horizontal or vertical insulation. And IESVE help...wasn't much help.

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I assume you mean insulation that has a sheet 24" down separate from a horizontal sheet the goes 24" in, as opposed to a single piece that is a 24" x 24" block around the perimeter. If it's the latter then you should just be able to enter it in, but you're right on the former - it's not technically possible. I'd email support just to register the wish and in case they have some better ideas, but I can think of two ways to approximate it. First, assume you have vertical only, but calculate the equivalent thickness to give you about the same performance of the horizontal. Or Second, only do vertical again, but add a very thin layer of insulation to the bottom of the construction, again based on a calculation getting equivalent performance. An idea to figure this out is to run a simulation with no insulation, then one with only the horizontal, and then one only defining the insulation in the construction to find the correct equivalent thickness. Depending on the purpose of your model that might all be overkill though, and the ground conduction calcs aren't the most accurate things anyway.

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Thanks. Ultimately, I think we're probably seeking a level of detail that is not going to make enough of a difference to make the juice worth the squeeze, so to speak.
As far as your recommendations, I would expect the second option to be a bit more straightforward. But instead of iterating in the software to find the equivalent performance, I think I would just do the hand-calcs or use Appendix A. In our case, I think we just picked either horizontal or vertical and decided that was sufficient for our purposes. Thanks again!

( 2021-03-18 06:45:17 -0500 )edit