Our annex has rain screen cladding too but it is minute in comparison:
click to enlarge
A great deal of thought went into the design of the annex by architect Stuart Green who specified zinc rain screen cladding for its appearance and for its ability to keep the weather out. I well remember him being asked by his assistant Maarten Kleinhout if there was to be insulation behind the cladding. Equally, I remember Stuart Green's instruction. No!