The extent of the property market slump last year is highlighted by figures issued by Quotable Value on Thursday.
House prices fell by 7.4% in 2008.
QV says property values grew by 54% between 1992 - 1997 and 120% between 2002 - 2007.
2008 saw a significant "correction" to prices. However, the agency is unsure when the period of falling values will end.
It says the correction was inevitable and a sustained drop of this size was last seen in 1998.
Despite the drop in 2008, QV says the market is making a better recovery than expected.
Meanwhile, figures from the Real Estate Institute show that only 4,302 houses were sold nationwide in December, compared with almost 5600 in the same period a year earlier.