Under the Michigan Energy Code, what is the minimum R-value requirement for wall insulation in Climate Zone 6A?
Correct Answer
D) R-20
Michigan Energy Code requires R-20 wall insulation in Climate Zone 6A, which covers most of Michigan's lower peninsula.
Why This Is the Correct Answer
Michigan Energy Code adopts the International Energy Conservation Code with Michigan amendments. Climate Zone 6A, which covers most of Michigan's lower peninsula, requires a minimum wall insulation R-value of R-20 (or R-13 continuous insulation alternatives under a prescriptive compliance path). R-20 represents the standard cavity insulation requirement for this cold climate zone.
Why the Other Options Are Wrong
Option A: R-13
R-13 is the minimum wall insulation requirement for warmer climate zones (Zones 1–4) and is insufficient for Michigan's Climate Zone 6A. R-13 is a common starting point for contractors familiar with southern states, making it a frequent wrong answer choice.
Option B: R-15
R-15 falls between R-13 and R-20 and does not correspond to the standard Climate Zone 6A wall requirement. Some compliance paths may accept R-15 with continuous insulation additions, but R-20 is the baseline cavity insulation requirement for Zone 6A.
Option C: R-21
R-21 exceeds the minimum requirement for Zone 6A walls. R-21 is commonly used for 2x6 stud walls (which can physically accommodate R-21 batts) and may be found in higher climate zones or enhanced performance paths, but R-20 is the code minimum for Zone 6A.
Memory Technique
Michigan = Cold = Higher R-values. For Zone 6A walls: '20 below zero in Michigan means R-20 in the walls.' The extreme cold climate demands higher thermal resistance. Zone number 6 → R-20 wall insulation — think of both numbers being in the 20s range.
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