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Restoration work at St Patrick's Cathedral in central Auckland will cost almost an extra $1 million and take about four months longer than first thought.
Instead of opening in April in time for Easter, the 160-year-old building will not open until August.
The cathedral on Wyndham St was shut in October last year when work was projected to cost $12 million.
Now, it is expected to cost nearer $12.9 million.
Cathedral business manager Kevin Sherlock and administrator Father Bernard Kiely said that part-way through the work it became obvious that some changes were necessary.
Four high arches at the intersection of the cathedral's transept needed extensive reinforcing and strengthening and this was only discovered as work progressed
"The arches were weaker than we thought," Father Kiely said.
The central aisle was also found to have a concrete tiled floor hidden beneath carpet and lino.
Auckland City Council's heritage section said this flooring had to be preserved because it was an original 1880s design.
An appeal was launched two years ago to pay for the cathedral's restoration and more than $9 million has been raised.
Workers from Fletcher Construction have painted the cathedral's cross at the top of its steeple and dismantled part of the scaffolding used for access.
The building was in a poor state before work started. Its roof leaked, walls were cracked and the structure was an earthquake risk.
The plaster-on-brick exterior had rising damp and plaster was crumbling from the walls.
