The minister said the licensing was the first in a number of steps aimed at tidying up the industry. The second step was protection for the consumer and that would be covered off with the Building Amendment Bill No 4 now before Parliament.
A number of industry sectors were recognised for their low productivity but the building industry was the lowest. "Surveys within the industry found vast numbers of those working in it were illiterate and innumerate," he said.
And there was also a lot of bureaucracy in place and "that didn't make sense to me".
"Up until March 1 this year all you needed to be a builder was a cellphone, a ute and probably a dog. And the country paid a big price for that sort of laxness."
Mr Williamson said there were too many and unnecessary local authority inspections involved. "Being licensed means the builder does not always have to get consents from the local authority for minor works and those companies who build a number of units of the identical specifications will not have to get consents for every home they build," he said.
The new law also allows do-it-yourselfers to continue to build or renovate their own homes while protecting future purchasers of the property. "The owner-builder exemption allows DIYers to continue carrying out building work but they must take responsibility for that work and this will be kept on the local council's property records for future owners to see."
Mr Williamson said better protection for the consumers was the aim of the bill now before the House.
He said the issue of liability was one area he was struggling to resolve. "Where building companies fold up and run, it does not seem right that the local bodies are the ones left carrying the can," he said.
He said the Law Commission was doing work in that area, largely driven by the fallout from the leaky homes saga. "To give you some idea of the impact of leaky homes, the Canterbury earthquakes will cost something like $20 to $22 billion. Leaky homes have cost $11.3 billion so far but are likely to be twice that when all manifest themselves."