Quotable Value says an increasing number of home owners are choosing to renovate existing homes due to a lack of quality, well-presented properties on the market.
The agency's house price index rose 2% in September, but the pace of growth is slowing. Values have fallen 1.4% since March.
Research director Jonno Ingerson says sales volumes are currently 30% below the long run average, as buyers and sellers remain cautious.
He says more owners are choosing to stay in their home and renovate, rather than move, which may be another reason why fewer houses are on the market as owners upgrade their property.
Mr Ingerson says the number of listings are likely to improve through the rest of spring and over summer, but sales are likely to remain muted and prices will continue to fall slightly over the next few years.
QV says house prices rose 2% in September, but the pace of growth continues to slow.
Values rose 3% in August but have fallen 1.4% since March, and are now almost 10% below the peak reached in November 2007.