House design · Detail the envelope · design-18

Specify windows and glazing

Windows are the weakest part of the envelope and the source of free solar heat. Choose glass by orientation and climate.

How

Compare windows using rated U-factor (lower insulates better) and solar heat gain coefficient, SHGC (lower blocks more sun heat) from the rating label used in your country.
Heating climates, sun-facing windows: high SHGC (DOE fact sheet suggests 0.60 or more) with U-factor of 0.35 or less in US units.
Cooling climates: U-factor below 0.4 and SHGC below 0.55 (DOE fact sheet), plus external shading.
East and west windows: low SHGC or shade them (DOE).
Use double or triple glazing with low-e coatings, argon fill and warm-edge spacers; aluminium frames need a thermal break (DOE).
Specify openable areas for ventilation and fire egress per local code, and insect screens in tropical climates.

Passive Solar Design (Technology Fact Sheet DOE/GO102000-0790). US Department of Energy and NREL, accessed 2026-11
Window Types and Technologies. US Department of Energy, Energy Saver, accessed 2026-11
Consumer Guide to Energy-Efficient Windows (DOE/EE-2468). US Department of Energy, Energy Saver, accessed 2026-11