Economists had expected a drop of 12.5 per cent, according to Thomson Reuters.
The federal agency said the drop was mostly due to fewer plans for non-residential buildings in Quebec and residential buildings in Ontario.
The value of non-residential building permits was down 40.6 per cent to $2.5 billion in August after four months in a row of gains.
Statistics Canada said seven provinces posted lower construction intentions, with Quebec having the most to do with the decline.
CIBC economist Nick Exarhos noted the drop in non-residential permits "will hurt some of the hopes reserved for a sustainable turn higher in business investment."
Institutional building construction plans fell 76.0 per cent to $446 million in August, after increasing 29.6 per cent in July and 149.3 per cent in June.
Meanwhile the commercial component saw the value of permits fall 12.1 per cent to $1.6 billion in August, following a 1.2 per cent increase in July. The industrial component dropped 15.2 per cent to $454 million in August, the second consecutive monthly decline.
On the residential side, the value of permits fell 15.9 per cent in August to $4.2 billion after five consecutive months of increases.
Statistics Canada said Ontario saw the largest decrease, followed by British Columbia and the Atlantic provinces, while Alberta and three other provinces recorded gains.
The total value of permits was down in six provinces in August, with the largest drops in Ontario and Quebec and, to a lesser extent, British Columbia, Statistics Canada said.
Canada Mortgage and Housing Corp. is expected to report housing starts for September on Wednesday.
According to Thomson Reuters, economists expect the annual pace of housing starts in Canada to come in at 196,100 for the month, up from 192,400 in August.