UPDATE 1-Canada building permits fall for third month

* Permits unexpectedly fall 4.9 pct in Sept from Aug

* Permits down 2.8 pct on the year

* Housing falls 1 pct m/m, nonresidential slides 11 pct

OTTAWA, Nov 4 (Reuters) - The value of Canadian building permits fell 4.9 percent in September from August, the third consecutive decline as construction intentions slowed markedly in Western Canada, Statistics Canada said on Friday.

Analysts surveyed by Reuters had on average forecast an increase of 2.8 percent in the month. Statscan revised its August data to show a drop of 10.1 percent versus 10.4 percent previously.

Overall permits fell 12.8 percent from a year earlier.

Permits for housing eased 1 percent on the month and 4.8 percent on the year. The worth of multifamily dwellings authorized by municipalities fell 2.5 percent while that of single-family units edged down 0.1 percent.

In nonresidential construction, permits tumbled 11 percent. Institutional projects declined the most, followed by commercial buildings, while the industrial component grew in value.

The value of overall permits fell across six provinces, with British Columbia and Alberta recording the biggest downturn.