A second investigation into the Bella Vista Homes mess in Tauranga is getting underway this week.

Tauranga City Council is turning its eye on itself, appointing retired judge Graeme Colgan to work out why its building inspectors approved the plans for the shoddy homes.

The 21 houses were too dangerous to live in, and residents were evacuated.

MBIE's also looking at the council's consenting process, while some homeowners are suing, and in return the council's suing Bella Vista Homes' director.

Tauranga Mayor Greg Brownless told Mike Yardley they hope to get to the bottom of it by Christmas.

"We don't really know what's happened, that's part of the problem. And of course, there is plenty of room for speculation that's why we are trying to get to the bottom of it, we just want to know the truth."

LISTEN ABOVE AS GREG BROWNLESS SPEAKS WITH MIKE YARDLEY