High-performance openings (windows, doors, glazing)

Ranked by U-value, how much heat the whole unit loses per square metre for each degree of difference between inside and out, so lower is better. Triple glazing with a low-E coating is the ceiling; each step down adds either a pane or a night-only layer. Note shutters and curtains work only while closed, so they cut night-time loss without improving the window itself.

Solutions

• Triple-glazed, low-E windows: Highest thermal performance glazing; heavier and costlier than double glazing.
• Double-glazed windows, insulated frames: Lower cost/embodied-energy alternative to triple glazing; still a large step above single glazing.
• Secondary glazing (retrofit inner pane): Adds a second pane inside an existing window rather than replacing it; relevant if starting from an existing building.
• Insulated operable shutters: Removable or foldable insulated panels over glazing at night, cutting heat loss when the sun isn't providing gain anyway.
• Electrochromic (smart) glazing: Low-voltage electrochromic coating between glass panes lets tint and solar heat gain be adjusted electronically rather than fixed at installation, unlike any st
• Insulated draft-blocking curtains: DIY window curtains built from an outer fabric layer and an inner reflective/insulating layer (e.g. mylar or foam-backed material), sealed to the window frame w