Calgary housing became slightly more affordable in 2009, but it's still just the 23rd most affordable place to own a home from a list of 28 Canadian cities, according to the Winnipeg-based Frontier Centre for Public Policy.

In a study released Monday, the centre found Thunder Bay and Windsor, both in Ontario, were tied for most affordable Canadian cities and Vancouver was the least affordable.

In fact, Vancouver was also the least affordable among the 272 cities in the international study, which covered Canada, Australia, Ireland, New Zealand, the United Kingdom and the United States.

As Canada's resale housing market boomed and prices rose in 2009, affordability fell, sending the national average to a reading of 3.7 from 3.5 the year before. (A higher score indicates less affordability).

That would place Canada's overall housing market in the "moderately unaffordable" category -- from 3.1 to 4.0. The numbers are calculated by dividing the median residential house sale price for the third quarter by median annual gross household income.

In Vancouver, for example, a median home price of $540,900 was divided by median household income of $58,200 to create a multiple of 9.3, which the group describes as "severely unaffordable" -- any reading of 5.1 and over.

Calgary, with an affordability index of 4.6, is just slightly less affordable than Prairie rivals Saskatoon (4.4) and Edmonton (4.1). On the international list, Calgary is 188th and its nearest neighbours are Eugene-Springfield, Ore.; Palmerston North-Manawatu, New Zealand; and Dundee, U.K. It's just slightly more affordable than Dublin, Ireland.

Calgary and Edmonton became fractionally more affordable in 2009 after climbing two points over the previous four years. In 2008, Calgary's index was 4.8 and Edmonton's was 4.2.

Toronto moved from a reading of 4.8 to 5.2, moving it into the severely unaffordable category, while Montreal moved from a reading of 4.6 to 4.9.

"Montreal is approaching severely unaffordable for the first time. It appears Montreal has caught up to its urban growth limit and this has now become a real constraint on land supply," the group said.

Victoria was second only to Vancouver, with its reading rising from 7.4 to 7.9, while Ottawa' hot housing market remained within the realm of the moderately unaffordable, at least as measured as part of the Ottawa-Gatineau metropolitan area, with a reading of 3.8, up from 3.4 the year before.