A building expert says people tend to focus on the cost of building infrastructure and think they'll figure everything else out as they go along. 

The Infrastructure Commission says we need to spend around 60% of our investment to look after what we already have, rather than building more. 

AUT Professor of Construction Management John Tookey told Mike Hosking that people often focus on acquisition costs, rather than maintenance costs because it's easy. 

He says that's because the sums get more complicated when you start considering the likes of depreciation and more over an extended period of time. 

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• Infrastructure report says majority of funding should be spent on maintenance