Yes - it's a metaphor. Within the reality of the poem, it exists, but the overall poem represents something else. The poem is about the physical destruction of a house, but I'm also intending to use that as a metaphor for broken family relationships. The first stanza is about that broken relationship, and the physical destruction of the house forces those traumatic memories back 'in the air'. The narrator thought that they had recovered from their childhood traumas, hence the 'second of paradise', before realising that they hadn't gotten over them at all.