In traditional British academic pronunciation, the adjective communal sounds more like the noun commune ('COM-youn', IPA: /ˈkɒm juːn/) than the verb 'to commune' ('kerm-YOUN', IPA: /kə (or ɒ)m ˈjuːn/). Communal is better pronounced with the stress on the first syllable ('KOM-you-nel', IPA: /ˈkɒm juːn əl/).
There is a growing tendency to pronounce it with the stress on the second syllable, 'kerm-YOU-nel' (IPA: /kə (or ɒ)m ˈjuːn əl/). (In 1988, this was the pronunciation preferred by 32% of a survey of British speakers reported in LPD.) AWE's preference, as so often, is in favour of the traditional version.