South Oxfordshire District Council to specify new housing sites
A planning inspector said proposals to site 800 new homes in Oxfordshire were "inconsistent with national policy".
The locations chosen by South Oxfordshire District Council could not be guaranteed to meet the district's housing needs by 2027, it was said.
The council must now bring forward more detailed proposals by 1 November on where the new homes should go.
Angie Paterson, cabinet member for planning, called the inspector's approach "a major disappointment".
She added: "We can't change the situation or the number of homes we have to provide.
"The next few weeks will see some important decisions made in moving this strategy forward and laying the foundations for a successful future for South Oxfordshire."
Council leader Ann Ducker said the council had been told to allocate all homes for the next 15 years to named sites.
She added: "We don't think this is within the spirit of localism, when we had found a solution that our communities supported."