It seems that only 2 different attic spaces can be modeled in the “Attics” section. How can we model more than 2 spaces? An example would be a 1.5-story home with a peak flat insulated to R-49, one knee wall flat insulated to R-11, and one inaccessible, uninsulated knee wall attic. Do I need to force these 3 spaces into 1 or 2 by calculating a weighted average of R-values across the combined sq footage?
Right, we only have controls to describe two open cavity attic spaces, so you will need to combine some areas. The approach would depend on what you are improving.
First off, if the R-49 area is just a small peak flat and you want to improve the other two, then you could just leave that area out of the model or treat it part of the sloped roof area.
If you want to model an improvement to all three areas or just the uninsulated portion, I would combine the R-11 and R-49 areas. If you just want to improve the R-49 or R-11 areas, isolate the area you want to improve and combine the others.