The region saw 374 starts in August 2012 compared to 650 in the same month last year, according to figures released Tuesday by the Canada Mortgage and Housing Corp.
Apartment-style condos, which fuelled last year's growth, plunged more than 80 per cent to 37 starts. Last August, starts stood at 187.
Overall multi-family starts fell by about 53 per cent to 203, while single-detached starts fell 20 per cent to 171.
Despite the large fall-off in August, housing starts in 2012 on a year-to-date basis are still 29 per cent ahead of last year's pace.
Ottawa recorded 4,459 starts so far this year, compared with 3,449 at the same time last year. Growth came mainly from apartment-style condos, which rose 195 per cent year-over-year so far in 2012.