Richard Alfred Milliken’s bawdy version of The Groves of Blarney suggests to me that a moss house might have been a bower where animals bred and where lovers would meet .Thus “where the birds do increase”

There is a cave there where no daylight enters,
Where cats and badgers are for ever bred,
All moss'd by nature, which makes it a great dale complater,
Than a coach and six, or a feather down bed

The Bunclody air is close to the one used for the English song Pleasant and Delightful, isn't it?