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Convert thermal transmittance (U-value) to thermal resistance (R-value) for building envelope analysis
Formula: R-Value = 1 / U-Value
Note: Lower U-values mean better insulation (less heat loss)
| Window Type | U (Imperial) | R (Imperial) | U (SI) | R (SI) |
|---|---|---|---|---|
| Single glazed | 1.04 | 0.96 | 5.91 | 0.17 |
| Double glazed (air) | 0.49 | 2.04 | 2.78 | 0.36 |
| Double glazed (argon) | 0.30 | 3.33 | 1.70 | 0.59 |
| Triple glazed (air) | 0.33 | 3.03 | 1.87 | 0.53 |
| Triple glazed (argon) | 0.20 | 5.00 | 1.14 | 0.88 |
| High-performance (krypton) | 0.15 | 6.67 | 0.85 | 1.18 |
U-Value (Thermal Transmittance) measures the rate of heat transfer through a building element. A lower U-value indicates better insulation performance. It's the preferred metric in European standards and international energy codes.
R-Value (Thermal Resistance) measures a material's resistance to heat flow. Higher R-values indicate better insulation. It's commonly used in North American building standards and product labeling.
Divide 1 by the U-value. For example, if U = 0.5 BTU/(hr·ft²·°F), then R = 1/0.5 = 2.0 ft²·°F·hr/BTU. The two values are mathematical inverses.
A LOW U-value is GOOD - it means less heat passes through, indicating better insulation. This is opposite to R-value where HIGH is good. Remember: Low U = High R = Better insulation.
U-values are standard in international building codes and energy modeling software. They directly represent heat loss, making energy calculations more straightforward. European and Asian markets primarily use U-values.
It depends on climate. Cold climates: U ≤ 0.30 BTU/(hr·ft²·°F) or 1.70 W/(m²·K). Moderate climates: U ≤ 0.35. High-performance buildings aim for U ≤ 0.20 or lower.
You cannot add U-values directly. Convert each to R-value (R = 1/U), add all R-values together, then convert back (U_total = 1/R_total). Only R-values are additive.
Installation quality (gaps, thermal bridging), frame materials, edge effects, age and condition, air leakage, and environmental conditions all impact actual performance vs. rated U-value.