Access conditions for H-modes with detached divertor plasmas are derived by considering power threshold, divertor plasma temperature and density limit constraints. It is found that there is a minimum scrape-off layer power and main plasma density for accessing the detached divertor H-mode, and that the required divertor radiated power fraction must increase as the machine size and field increase. The model describes, at least qualitatively, experimental findings on ASDEX-Upgrade, DIII-D, JET, and JT-60.