The sale of Christchurch's threatened McLean's Mansion to the Heritage Trust is expected to go through before Christmas.

Ten million dollar quake repairs are set to begin immediately to turn the 53 room house into an art gallery.

This comes after the city council voted to grant 1.9 million to the trust towards repairs.

Heritage Trust Chairman Trevor Lord said some rooms should be ready in nine months.

He said McLean's Mansion is one of the biggest wooden houses in the world and was originally built to the standard of a palace - so it's likely to draw plenty of visitors.