Last month, this column argued that Ireland has spent the best part of a century building a housing system for a single tenure. Ownership has been the destination – private rental and social rental have been treated as little more than the waiting room and the safety net. A healthy housing system, in other words, rests on three healthy pillars, not just one. I write regularly, both here and in the Daft.ie Report commentaries, on challenges facing the private rental pillar. But what about the third pillar, social rental? That June piece closed on the idea that fixing the social…