In Barot's trial, police said they found a one-day reading pass to the Portland Place building in his possession when they arrested him.
They believe that he used the library to find architectural magazines to research the plans of buildings he wanted to attack.
These targets included the New York Stock Exchange, for which Barot had photocopied architectural drawings of the plans of the first and second storeys in his possession.
Woolwich Crown Court earlier heard that Barot's grand design was to destroy five of the USA's most important financial institutions in a series of devastating simultaneous explosions.
After Barot finished checking out his targets, the court heard, he drew up detailed documents setting out their layout, security measures, access and escape routes as well as a host of other information.
Barot would have been able to garner much of this information from the RIBA library.
Barot, 34, received a life sentence earlier this week after admitting conspiracy to murder.