The $1.26 million seismic upgrade of Diocesan School for Girls' old chapel will be finished around mid-May.
School principal Heather McRae and business and planning director Merle Boniface said Aspec Construction's work on the Chapel of Our Glorified Lord was creating a building up to the same standards as new structures or 100 per cent of the building code.
The chapel, joined to the smaller wooden historic category 2 St Barnabas' Chapel which was moved to the school site from Parnell, was two skins of brick wall with an interior and exterior plastered finish.
Buildings like this are considered high earthquake risks.
The unreinforced masonry structure with a timber interior roof was build in 1922. Weak brick walls have been strengthened and tied into the roof and floor structures.