Windows are a big deal for performance.

The U.S. Department of Energy's chief architect underscored what building scientists have argued for years: windows are one of the biggest levers on a building's energy performance.

In most assemblies, the windows are the weakest thermal link in the envelope — the place where heat most readily escapes in winter and enters in summer. That makes glazing choices disproportionately important to both comfort and energy use.

It's a point we return to often: you can invest heavily in walls and insulation, but mediocre windows will cap the performance of the whole building. High-performance glazing is what lets the rest of the envelope do its job.