Hoardings have been put up round Town Church in St Peter Port in preparation for major renovations and repairs.
The hoardings are up at the church on St Peter Ports's seafront
The cost has been estimated at more than £800,000, and work is expected to take 46 weeks to complete.
Work will be carried out to the roof, spire and bell tower and there will be external redecoration and gilding to the clock faces.
The roof timbers of the church, which date back to 1048, have been destroyed by death watch beetles.
The cost of the renovations has been raised in advance through parish rates.
Repairs carried out to the church in 2000 caused controversy and the matter was referred to Guernsey's Ecclesiastical Court.
Lindsey Mellor, the wife of the Dean of Guernsey Canon K Paul Mellor, said she expected there would be much rejoicing when all the work has been finished.
She told BBC News: "The hoardings are up now and, although the work could lead to some disruption because the church is on the seafront, there is great excitement now the project is under way."