An average U-value calculator,
rebuilt and shared for free
An Excel workbook built to MOLIT Notice 2025-738 (effective 31 Dec 2025), Table 1. Enter each material and its thickness, and it returns the per-part U-value, the area-weighted average, and the compliance check. Two Central-2 zone presets are included: apartment and non-apartment.
Free download
Average U-Value Calculator v2026
Excel (.xlsx) · Tables 1/2/4/5 built in · 8 assembly types + 9 window/door types
Switch the region and building type on the cover sheet to reuse it for other zones and uses. Read the notes below before you rely on it.
Why rebuild it
No more spreadsheets you fill in by hand
Most U-value templates in circulation are hard-coded: every number is typed into its own cell. Change the zone or one assembly and you have to re-edit each related cell by hand, and a wrong reference value never shows. A single mistyped conductivity can follow the sheet all the way into the permit set.
So this one is built around the calculation instead. The reference values live in one place (the Standards DB sheet) and every other sheet reads from it. Pick a region and building type on the cover, and every part's reference U-value updates at once. You only ever touch the orange input cells.
How it works
Two formulas are all it takes
1. Per-part U-value
U = 1 / ΣR
The reciprocal of all surface resistances plus each layer's resistance (thickness ÷ conductivity). Choose a material, enter the thickness, done.
2. Area-weighted average
Û = Σ(U·b·A) / ΣA
U weighted by area. Parts facing outdoor air indirectly take a correction factor b = 0.7. Centre-line dimensions.
Data flow
- 1
Pick region & building type on the cover
Central-2 / Apartment → Table 1 values link across every sheet.
- 2
Enter material & thickness per assembly
Material from a dropdown, thickness as a number. Conductivity, resistance, U-value and pass/fail compute automatically.
- 3
Enter areas on the average sheet
Pick a section code to pull its U-value; enter area to get wall, roof and floor averages.
- 4
Read the result on the cover
Per-part and average results, with compliance, gathered on one page.
Contents
Seven sheets
| Sheet | Role |
|---|---|
| 00 Cover | Project info; average results and per-part compliance summary |
| 01 Standards DB | Tables 1/2/4/5, the source every sheet references |
| 02 Materials DB | Material conductivity list, source of the dropdowns |
| 03 Assemblies | 8 wall / roof / floor parts, material & thickness input |
| 04 Windows & doors | 9 types; certified U-value and airtightness grade input |
| 05 Average U | Area-weighted average for wall, roof and floor |
| 06 Revision notes | What changed under 2025-738, and things to verify |
What changed
The 2025-738 revision, briefly
The reassuring part first: the per-part U-value limits have not moved since 2018. Values like 0.170 W/m²K for a Central-2 apartment external wall still hold.
What actually changed:
- ·Zone names & boundaries — renamed to Gangwon / Jeonbuk Special Self-Governing Provinces; Gunwi-gun (Daegu) moved into the Central-2 zone.
- ·Primary energy demand tightened — 200 → 150 kWh/m²·yr for buildings ≥ 1,000 m², effectively steering design toward ZEB grade 5.
- ·Minimum EPI points per section — architecture, mechanical, electrical and renewables each carry a floor.
- ·ZEB linkage — a preliminary certificate exempts the design review submission.
Fuller notes, plus the conductivity typos found and fixed in the original template (extruded board no.3, rock wool no.2, glass wool 24K), are on the 06 Revision notes sheet.
Before you use it
This is a design-review tool — good for setting up the basis of calculation quickly and comparing assemblies.
It deliberately leaves out the submission forms (energy performance index sheets, general and mandatory items), because those change with each revision of the standard. Download the current forms from greentogether.go.kr or EAIS, and attach this workbook as supporting basis.
Insulation conductivity should come from the manufacturer's test report. Enter it in the ‘certified λ’ column on sheet 03 and it overrides the built-in DB. Cross-check EPI point bands against the current notice's scoring table directly.
Grab it and try it
Two Central-2 presets. Other zones switch from the cover dropdown.
Found an error, or want another assembly or window type added? Let me know — real use always turns something up, and that feedback shapes the next version.