Passive
Sealing the gaps air already moves through in a house that stands: around window and door frames, at skirtings and floor edges, around pipe and cable penetrations, at loft hatches and unused chimneys. Distinct from the airtight membrane laid during construction, which you only get one chance at; this is the retrofit version, done with caulk, tape, foam and brush seals, from the inside, an afternoon at a time. Usually the cheapest meaningful reduction in heat loss available, and the one to do before adding insulation rather than after. The limit is ventilation: a house sealed without a deliberate way to change its air gets damp, so this belongs alongside trickle vents or extraction, not instead of them.
One of 2 ways to meet Airtightness. Build 1/2, Upkeep 2/2, Efficiency not rated. Cost, carbon and footprint below are rated against those 2, not in absolute terms.
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Every option in this sub-function, with the value on each axis and a note on what drives it (this solution highlighted):
| Solution | Build skill | Upkeep burden | Efficiency |
|---|---|---|---|
| Airtight membrane with taped/sealed joints | N/A | 2 | N/A |
| Draught-proofing an existing house | Basic | 3 | N/A |
Build skill and upkeep burden are proxies (lower burden = simpler to maintain); the efficiency column is this sub-function’s ranking, 1 = best. “N/A” where an axis isn’t rated here.
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.