Rents on prime offices in Belfast increased by 12% in 2014 to as much as £15 per square foot, research has found.
Research by commercial property agents Lambert Smith Hampton found that rents in Belfast had borne the second-largest jump in the UK after the south east of England.
But the agency said new build developments of office space were still not viable for private developers, who still struggled to secure funding from banks.
In fact, the agency said rents would need to go up by 20% in total - and that Belfast would still be competitive compared to other cities if there was such an increase.
Stuart Draffin, director and head of agency at Lambert Smith Hampton in Belfast, said: "This report provides encouragement that the market is improving, with prime rents up 12% in Belfast last year, one of the strongest regional increases outside of the south-east of England.
"We have already seen rents of £15 per square foot in some properties and would expect this to rise during the year.
"Office rental growth will eventually encourage new development and this in turn will drive other parts of the market as the residual value of potential development sites increases to allow redevelopment of old or secondary uses. However, despite a healthy demand for Grade A office space and a limited supply of that space, the most recent lease terms secured still don't yet justify new build activity. Banks are definitely keen to discuss proposals again but it is understandable they are nervous about speculatively supporting a new build scheme that would require rental terms previously not seen before in Belfast to make it viable."