The level of deterioration differs from region to region and between types of homes, but for the average bungalow the affordability measure rose 0.7 of a percentage point to 43.3 per cent nationally in the third quarter, after a 0.3-percentage-point gain in the second quarter.
That means the average household would have needed to devote 43.3 per cent of its pre-tax income to service the cost of owning a bungalow at current market values, including mortgage payments, utilities and municipal taxes. The higher the rating, the less affordable a home is to any particular family.
For two-storey homes, the affordability reading rose 0.6 or a percentage point to 48.9 per cent in the July-September period.
Owning a condominium was the most affordable option, with a cost measure of 28 per cent of pre-tax income, and the most stable, up just 0.1 of a percentage point from the previous period.
RBC chief economist Craig Wright attributed the deterioration in affordability to higher prices and what has been a tightening mortgage market reacting to an expectation of firming interest rates.
"By the third quarter, strong resale activity across Canada heated up home prices a few degrees," he explained. "At the same time, Canadian bond yields rose in tandem with those in the U.S., climbing in anticipation of the Fed (U.S. Federal Reserve) tapering its bond buying program."
The most recent Canadian Real Estate Association report pegged the average resale price of a home at $391,820 in October, 8.5 per cent more than a year earlier.
Wright said recent months has seen a divergence in prices for Canadian homes, with price gains for bungalows and two-storey structures outpacing condominiums.
Affordability deteriorated in many of the large markets, but while the average number is only moderately higher than historic norms, RBC notes there is a wide disparity in the associated costs depending on markets, with some appearing out of reach of the average family.
It would take 84.2 per cent of an average household's pre-tax income to maintain a home in Vancouver, a rise of two percentage points from the second-quarter reading.
In Toronto, the affordability measure rose 1.3 percentage point to 55.6 per cent, the second worst in the country.
Most other major markets had affordability scales that were closer to historic norms: Montreal rose 0.3 of a point to 38.3 per cent; Ottawa was up 0.4 of a point to 37.3, Calgary up 0.7 of a point to 33.7 and Edmonton up 0.5 of a point to 32.9 per cent of household income.
The report says the biggest risk to maintaining manageable affordability levels would be a sharp rise in interest rates, but many analysts believe that is unlikely to occur as long as global economic growth remains moderate and inflation pressures soft.
The RBC says it does not expect the Bank of Canada to start hiking rates until sometime in 2015 as bond yields, the main driver of fixed mortgage rates, are projected to drift only "gently" upwards in the next year or so.