Builders broadly agree with the Commerce Commission's findings that law changes are needed to fix a lack of competition.
In the past year, StatsNZ said the cost of construction materials have gone up by nearly one-fifth
The Commission looked at three key building supplies - concrete, plasterboard and structural timber.
The draft findings published today said supply was too concentrated, and was too hard to introduce new or alternative products to the market.
The Registered Master Builders Association chief executive David Kelly spoke to Charlotte Cook.