According to what I can find, an undercroft was also occasionally used for commercial purposes, whereas 'loch' was purely for storage and was not vaulted but carved out of soft stone. 'Basement' would be a synonym
http://en.wikipedia.org/wiki/Basement - specifically for 'loch', the fact that they are fashioned from the surrounding stone should be made clear, IMO, otherwise it is just a 'podzemí' (as in Brno and other cities)
http://www.europointbrno.cz/index.php?nav01=4076 - that would be better described as 'undercroft', and many of them were indeed used as shops as well as storage space.