Solution
As a rule, in conservation areas, the most you can expect is a single-storey extension. However, there can be an exception to this when – as is quite common in some parts of London – the house has a lower-ground floor and so an extension on top of the existing extension would be on the same floor as the main entrance.
Even so, the new extension needed to feel subtle and in keeping with the area. To help it blend in better, we decided to reclad the lower-ground-floor extension to match what we were proposing above it. Pre-application advice from the council steered us to a final choice of a zinc shell with timber slats providing privacy for the bathroom window. A new green roof on top of the original extension reinforces the idea that it is part of the garden, and connects the lower ground and ground floor extensions
In terms of square metres added, this is unquestionably very modest. In terms of improving the livability of the house, on the other hand, the impact is significant - the addition of a new, light-filled bathroom. And that was done without any sense that a historic building was being made any less beautiful.