The number of schools over which the State is suing construction company Western Building Systems has risen to 24, RTÉ News has learned.
The schools are among 42 built by the Omagh-based company in recent years where serious structural defects were discovered.
The bill for remediation work, which is ongoing, is now expected to run to many millions of euro.
The Department of Education has said that work to permanently fix 22 of the schools will be completed by the end of this year.
Fire safety remediation work will also be completed in all of the schools affected by then.
Two of the 42 school buildings are no longer in use as schools.
A third building, at Ardgillan Community School in Balbriggan, Co Dublin, has remained closed since defects were first discovered in 2018.
The department said that a contractor will be appointed in coming months to carry out remediation works at Ardgillan.
It said that work on this building, as well as the remaining 17 others will commence in 2021.
The department said it was not possible as yet to estimate the cost of all the work.
By September of last year, €40m had been spent on remediating the schools and related work.
The final bill will be much greater than that.
Work to fix the faulty buildings has been taking place in the evenings and during school holidays.
The Covid-19 school closures have meant that contractors were able to begin work on some of the schools slightly earlier in very recent weeks.
The department said that any disruption to schools while work is ongoing will be kept to a minimum.
