Korean insulation code in plain English

Central2 (Seoul, Incheon, most of Gyeonggi) demands U ≤ 0.17 W/m²·K for an exterior wall directly exposed to outside air. A 2x6 stud wall packed with glasswool 24K (140mm) does not pass. The calculator gives U = 0.250. Significantly short.

So how do you actually pass? Three approaches.

Path 1. Add exterior insulation (most common)

2x6 (140mm) interior + OSB + 50–75mm XPS or PIR outside. U drops fast.

Path 2. Bigger studs (2x8)

2x8 (184mm) with high-density glasswool 48K. No exterior layer. U about 0.179 — passes Central2 with no margin. Higher framing cost.

Path 3. PU spray foam

λ = 0.024. R = 5.83 in 2x6. Passes alone. But: 4–5x material cost, condensation risk in humid environments, and additional fire review for multi-unit/commercial.

Bottom line

Insulation has two layers of truth: passing the code (U-limit) and real performance after thermal bridging. Build to pass alone and you may face condensation later. Use the R/U calculator for first-pass verification, then have a licensed architect redo the official drawings with thermal bridging factored in.