Half of a new building’s "life energy consumption" is used during its construction. Demolition and sloppy building practice produce a mountain of waste three times greater in volume than the UK's domestic refuse! (Cindy Harris & Pat Borer, The Whole House Book, CAT Publications 2005).
Conserving existing buildings, whether or not they are listed or of great historic value, contributes significantly to reducing energy consumption. We manage rubbish, use standard sizes of materials, source locally, specify “forested” timbers and repair existing elements rather than replacing them.
The illustration brings into question the principles of SPAB repairs. It would be a great loss to strip and restore this scullery door and lose the layers of paint, towel roll, hooks and overshelf. The conservation principle here would be: leave it alone.