The cost of the latest repairs to the roof of St Peter Port's Town Church has risen to more than £800,000.
Ratepayers approved a further £309,000 for extraordinary work at a church meeting on Monday night.
The roof timbers of the church have been destroyed by death watch beetles, and a fibre optic video survey revealed the bell tower was unsafe.
Dean of Guernsey, the Very Reverend Paul Mellor, said it was important to keep the church in good condition.
He said: 'It's only the beetles holding hands keeping the roof up."
Cannon Mellor added that it would be most cost-effective to tackle the major problems together in a businesslike fashion.
He said that lessons had been learnt after controversy during church repairs in 2000 led to the matter being referred to Guernsey's Ecclesiastical Court.