The cost of reinstating the Christ Church Cathedral has jumped $20 million.

The Cathedral Working Group's estimate was $104 million to bring the cathedral back to its former glory.

In the Church Property Trustees management report to the Anglican Synod, funds required for reinstatement top $127.2 million.

So, what's the extra cash for?

Christchurch Property Trustees manager Gavin Holley said all additional costs were acknowledged by the working group, but not included in the final mock up.

He said it's been known for some time there will be other costs on top of the $104 million project cost.

Extras include a three person CPT-lead project leadership team, office space, as well as ongoing insurance and maintenance costs.