Thanks to Graham Everett for drawing our attention to this useful Briefing paper which has links to other resources and organisations involved in empty homes work, including short-life bodies and co-ops as well as RSLs.
National Indicators (N170 etc)
This contains the indicators relevant to empty homes, such as NI155 and NI170
NB this Word document is nearly 2MB in size.
This is the web-page, from where you can download the document itself.