Adds a second pane inside an existing window rather than replacing it; relevant if starting from an existing building.
Cost
Low
Upkeep
Occasional
Skill to build
Basic
Lifespan
20-30 years, same sealed/hardware failure modes as primary glazing
Embodied carbon
Low
Space / material use
Low
Output timing
None
Skill to repair
Basic
Regulation (FR example)
Changing the external appearance of an existing building normally requires a prior declaration (declaration prealable) at the mairie; stricter rules and an architect consultation apply within a protected or heritage perimeter.
Note: Cost, carbon and footprint are rated against the other options for this same need, not in absolute terms.
What your site needs
An existing window to retrofit (relevant only if starting from an existing building)
Inputs
none
Outputs
none
Sources
Glazing industry lifespan sources (Glass & Glazing Federation guidance via Everest/Gowercroft consumer glazing sites)
What this page does not tell you
No sizing or quantities: how much a technique yields, and how much a household needs, both depend on the build and the people, so the catalogue compares options rather than dimensioning them. It carries no bill of materials and no build sequence, and it is written for an oceanic, clay-soil climate (Normandy, France). Regulatory notes are indicative and need confirming locally.