Conservation consent is needed to demolish a building in a conservation area, but is not needed to alter or extend it. At what point do works of alteration amount to demolition works?

United Kingdom
This distinction was at the heart of the House of Lords' decision in Shimizu (UK) Limited v Westminster City Council (1997) and although the case arose out of a claim for compensation for refusing listed building consent it is of particular relevance in conservation areas.
It is, of course, difficult if not impossible to draw a rigid distinction between alteration and demolition unless demolition is to mean pulling down the whole of the building. The court, quite understandably, refused to go that far preferring instead to say that it must be a question of fact in each case. The judgement does suggest, however, that even if works of alteration do involve an element of demolition (as will very often be the case), conservation area consent will not necessarily be required on that basis. In the Shimizu case it was the removal of chimney breasts and stacks that was at issue.