The overcrowded conditions of the library was one of the reasons why the RIBA moved from 9 Conduit Street to larger premises at 66 Portland Place in 1934. The library remained open throughout World War Two and was able to shelter the archives of Modernist architect Adolf Loos during the war.

Answer this question, if possible (if impossible, reply "unanswerable"): What was the RIBA Library's fourth address?
unanswerable