According to the latest S&P/Case-Shiller index, which measures property prices in 20 cities, overall value in homes has now dropped by 18.4 per cent since the market's peak in July 2006.
The monthly survey has not registered a single overall increase in value since August of that year.
May's fall is also the sharpest on record since the index began taking results in 1987 - and houses in Detroit are now thought to be worth less than they were in 2000.
Speaking to the Times, chief US economist at High Frequency Economics Ian Shepherdson said: "We can't be sure this data is reliable over such short runs but they do seem to suggest the rate of decline of existing home prices is slowing.
"To be sure, prices are still falling very rapidly, and there is no prospect of any rebound this year and probably next, but a slower rate of fall is welcome nonetheless."