I can’t speak for the Irish, but the Scots’ tradition is to link such blessings to the idea of hospitality. Celtic culture in general is very big on the idea of hospitaility, a guest is a sacred thing and the rapport between a guest and his/her host/hostess is not to be trivialized. By this measure, a blessing would be appropriate whenever the person speaking it percieves himself (or herself) as a “guest,” private homes, taverns, inns, etc.
Functional, public spaces don’t really have the concept of guest and host in play so blessing a post office, library or factory, etc. would sound a little strange.