Australian construction activity expanded at the fastest pace in nine years last month, led by a boom in housing and a recovery in commercial building, according to a survey released on Tuesday. The overall index of construction activity jumped 4.1 points to 59.1 in September, well above the 50 threshold that separates growth from contraction, the report by the Australian Industry Group and the Australian Housing Association showed. That led to the highest rates of increase in employment and deliveries from suppliers since the survey began in September 2005, the Australian Industry Group said. “Continuing strength in house and apartment building and a consolidation of improved conditions in commercial construction outshone a further, modest contraction in engineering construction,” its director of public policy, Peter Burn, said. “In positive signs for the remainder of the year, new orders were strong in the three expanding sub-sectors and employment grew very solidly.” Low mortgage rates have helped to revive the housing market with the survey’s measure of house building up 0.8 points at a very high 61.7. The measure for the volatile apartment sector dipped 4.4 points month on month, but was still strong at 60.5. The commercial sector extended its recovery with that index up 3 points to 58.4. The survey’s measure of employment surged 9.1 points to 62.8, the highest on record.