Insulation: R-Values, and the Table Number That Moved

Prescriptive minimums by climate zone, plus the edition trap that sends people to the wrong table entirely.

2021 IECC minimums (ceiling / wood-frame wall / floor)

Zone 0-1	R-30 / R-13 / R-13
Zone 2	R-49 / R-13 / R-13
Zone 3	R-49 / R-20 or 13+5ci / R-19
Zone 4 except Marine	R-60 / R-30 or 20+5ci / R-19
Zone 5 and Marine 4	R-60 / R-30 or 20+5ci / R-30
Zone 6	R-60 / R-30 or 20+5ci / R-30
Zone 7-8	R-60 / R-30 or 20+5ci / R-38

Reading the notation

13+5ci	R-13 in the cavity PLUS R-5 continuous over the framing
ci	Continuous insulation, unbroken by studs
Why both are offered	They are ALTERNATIVES. A cavity-only option usually exists alongside the continuous one, so check both before paying for exterior board you may not need.

The trap: the table number changed between editions

In the 2021 IECC the R-values are in TABLE R402.1.3, and R402.1.2 holds the U-factor criteria.
In the 2018 IECC it is the other way round: TABLE R402.1.2 is the R-value table.
So looking up 'R402.1.3' in a 2018-adopting state lands you on U-factors and you will read them as R-values. The citation is right and the SCOPE is wrong, which is the hardest kind of error to spot.
Check which EDITION your jurisdiction adopted before you check which table.

This is the single most adoption-sensitive card on the site. Many states are still on the 2018 or 2015 IECC, or have amended individual values, or have reassigned counties between zones. Climate zones are assigned by county from ASHRAE Standard 169 and you should look yours up rather than infer it from local weather. Verify the adopted edition and the county zone map with your building department before specifying anything.

Sources: iccsafe.org · energycodes.gov

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