Code allows you to reduce the effective R-value of above-grade walls, as long as an equal amount of area has increased effective R-value to offset it. In no cases is the effective R-value in a wall permitted to be reduced to less than 55% of that required.

Photos Source: Summerhill

9.36.2.11. (1) Subject to limitations stated in Sentences (6) to (8), the trade-off options described in Sentences (2) to (4) apply only to above-ground building envelope components and assemblies, or portions thereof, of a single building.

Check with your local authority having jurisdiction as not all areas permit trading off of R-values. Trade-offs are basically when one area is insulated to a higher level in order to off set an area with an R-value lower than required by the ABC. This can only be done for areas above ground. Therefore the areas beside stairs going to the basement are not permitted to be reduced.

Note: The ABC lays out the requirements for calculating trade-off values for areas with reduced R-values. This is discussed more in the advanced course.